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Heating glossary

Click the letters below to find a wealth of heating information and jargon busting advice!


A material can be absorbent. It is any material that extracts one or more substances from a fluid – like a gas or a liquid – upon contact with that material.


A formal recognition of an agreed standard that shows that an organisation or a product is certified as competent to perform specific processes, activities or tasks.

Active Cooling

This is the use of mechanised heat pumps or pipes to transport warmth by constantly circulating heat transfer fluids.


Is the mixture of gases surrounding the planet, forming its atmosphere. By percentage, air in the atmosphere is made up of around 21% oxygen, 78% nitrogen and 1% of various other gases.

Air Collector

Used in solar heating systems, this is a type of solar collector in which air is heated up in the collector itself.

Air Conditioner

As the name may suggest, this is a device used to condition the temperature of air in an interior space. Designed for installation in a wall or window, its primary job is to provide conditioned air to that room without the need for ducting.

Air Conditioning

With the use of an air conditioner, it is the control of the quantity, quality and the overall humidity and temperature of the air in any interior space.

Air Diffuser

An air diffuser is an air distribution outlet that is typically found at the top of a room in the ceiling, they are designed to mix conditioned air with room air.

Air Infiltration Measurement

When auditing the energy efficiency of a building an air infiltration measurement is taken to determine or locate any air leaks that may be affecting the performance of the building.


An airlock is a blockage in your pipework caused by an air bubble.

Air Pollution

Air is polluted when the level of contaminants in the air prevent its normal dispersive abilities – resulting in interference with biological processes.

Air Quality Standards

Legislation that is set out to govern the level of pollutants that are allowed in the air – both the air inside and the air outside is governed by this legislation.

Air Source

A process in which heat is extracted from ambient air and then transferred to a different medium.

Air Source Heat Pump

A heating pump that helps to transfer heat from the outdoors to inside during the winter, and does the reverse in the summer.

Air-To-Water Heat Pump

A pump that transfers the heat in the air outside to the water of a property for the purpose of space or water heating.

Air Vented Valve

A simple mechanical device that will automatically release air that has been trapped inside your radiator (see also Bleed a Radiator).


A mixture of two or more metals.


A glamorously designed radiator from Milano Heating. Makes for a stunning addition to any modern interior.

Alternative Fuels

These can be any ‘non-conventional’ fuels that are derived from natural gas – such as propane, compressed natural gas etc, or biomass materials too.


The most common metal on earth, lightweight and durable, it is used in the construction of many modern radiators.

Ambient Air

The external air to a building or device.

Ambient Temperature

The temperature of any medium – like a gas or a liquid – that surrounds an apparatus or building element.

Angled Radiator Valve

Angled radiator valves do exactly what they say on the tin, they connect a radiator or towel rail to the pipework at an angle, generally 90 degrees. They are normally used when the pipework comes from the wall or below the floorboards.

Annual Service

Just like with your car, your boiler and central heating will need to be looked at least once a year (annually) to ensure it is running safely and efficiently.


Not only is this one of the most popular finishes to a huge range of designer radiators, but it is also a hard and dense type of coal that is hard to break, tough to set alight and burns with hardly any smoke due to its high concentration of fixed carbon molecules.


A chic and contemporary radiator collection from designer heating specialists Milano Heating. Rounded panels make this a clean and understated radiator design, that is on trend and suitable for any space.

Atmospheric Pressure

The pressure exerted by the weight of the atmosphere on to the earth and the objects located there.

Available Heat

The total amount of the heat energy that may be converted into energy from any fuel.

Back Boiler

A boiler usually made from non-ferrous metal, situated behind a real fire. Used with a direct cylinder.


The flow of water in the wrong direction due to a loss of system pressure.

Balance a Radiator

You can ensure that heat is evenly distributed through your heating system by adjusting the lockshield valves on your radiators so that they all run at the same average temperature and each takes the same amount of time to heat up.


Is a measurement of atmospheric pressure that is equal to the pressure you feel at sea level on earth. This measurement has replaced the older unit of ‘one atmosphere’, which is equivalent to 1.013 BAR.

Baseboard Radiator

A type of radiant heating system that has been designed to fit along an exterior wall where that wall meets the floor – quite a popular choice for heating modern conservatories.

Base Coat

A flat, bottom coat of paint over which a layer of glaze is usually applied.


Any plant or animal matter that is used directly as a fuel, or any that has been converted into other fuel types before combustion.

Blanking Plug

Simply a plug that can be fitted to an unused inlet on a radiator or heated towel rail, used to both seal and close the opening.


To bleed your radiator, is to expel air from the system using a radiator bleed key. Air can often make noise and will make your heating less efficient, bleeding your radiators will help to ensure this doesn’t happen.

Bleed Key

It is a bleed key that you must use to bleed your radiator. Some valves may be bled with a screwdriver, but most will require a bleed key to be inserted in order to operate correctly.

Bleed Valve

A bleed valve is normally located at the top of your radiator or heated towel rail. You use this valve to expel air from your radiator, making it more efficient.


A boiler is a closed vessel in which water is heated before being distributed around your home via pipework. Boilers do not ‘boil’ the water though, the heated or vapourised fluid exits the boiler for use in a variety of heating applications, such as radiators or heated towel rails.

Boiler Cycling

This happens when a heating system has reached its temperature and the boiler shuts down. A few minutes later the boiler will again fire up in order to top the temperature up as the system loses heat. Once this has been done, the boiler will shut down again. This constant firing and shutting down as the water cools wastes a lot of fuel energy.

Boiler Feedwater

This is the water that is forced into your boiler to replace that which has been lost through steam generation.

Boiler Noise Silencer

A liquid solution that can be added to a central heating system or electric radiator to help minimise noise when the water begins to reach temperature in the radiator.

Boiler Pressure

Normally measured in BAR (see above), this is the pressure of the steam or water in your boiler and heating system at any time. You’ll normally be able to tell what your pressure is set at by viewing the gauge on or below your boiler.

Boiler Rating (see also SEDBUK)

This is the heating capacity of a steam boiler. Normally expressed in British Thermal Units per hour (BTU/h).

Boiler Thermostat

Basically, this is a thermostat within the boiler casing that will limit the temperature of water passing through the boiler by switching it off. This temperature can be set by the user or may be fixed by the manufacturer.


A charming collection of radiators that scream timeless elegance. From Milano Heating and available in a range of finishes the Bora is a home heating classic. Bore – The hollow part of a pipe


Anyone thinking of purchasing a radiator should look for the BSEN442 mark. This will verify if a radiator or heated towel rail conforms to European standards and shows that the heat outputs of these products have been independently verified.


BTU stands for British Thermal Unit. It is the amount of energy needed to raise the temperature of a single pound of water by one degree Fahrenheit. You’ll need to calculate a radiators BTU output to ensure it is high enough to heat your room.

Building Regulations

Building regulations or ‘regs’ are statutory instruments that seek to ensure that the policies set out in relevant legislation are met and carried out. Most building work in the UK will normally require building regulation approval.


Another stunning collection of designer heating from Milano, the Capri takes its name from the island off the coast of Italy and just like that little island, is the epitome of understated style.

Carbon Monoxide

A poisonous gas known as the silent killer, because you can’t see, smell or hear it. It is created from improperly burnt fuels like gas, coal and wood and causes around 50 deaths every year in the UK.


Not an essential part of a boiler working, the casing is the surround that protects the inner workings of the boiler.

Cavity Wall

This is a wall made of two separate and parallel masonry skins with a section of air space in between.


A minimalist designer radiator from Milano Heating, the Cayos is an instant style pick-me-up that combines designer styling with an impressive heat output.

CE Marking

A CE Marking is the declaration by any manufacturer that a particular product meets all appropriate European Directives. It shows that a product can be legally sold in the EU.

Celsius (°C)

A common unit of temperature that has a zero point, which corresponds to the temperature at which water will freeze.

Centre to centre

Measuring from the centre line of one pipe to the centre line of another in order to make all of the tube centres appear uniform. This ensures that the pipework looks perfectly parallel.


The overall distance between the tappings on a radiator.

Central connection

Radiators or towel rails that have their valve inlets at the bottom and the centre of the underside of the radiator. These are opposed to regular valve inlets, which are normally found at either side of the radiator.

Central Heating

Hot water is heated in a ‘central’ boiler and then circulated through the radiators in a building. There are two main types of radiator – single-pipe and double-pipe – the former working with steam and the latter with steam or water.

Central Heating Flow

This is the heated water leaving the boiler and the same water entering the radiators.


A groove that has been cut into masonry or plaster into which electrical cabling or pipework is fitted.

Check Valve

See Non-return valve.

Chrome/Chrome Plating/Chromium Plating

Chrome is applied in a thin layer to a surface to help prevent corrosion of the plated material and improve both appearance and maintenance.


Radiators require a certain amount of space underneath in order for them to adequately heat a room and operate correctly. The recommended (minimum) height (or clearance) from the base of the radiator to the floor is 150mm.

Closed Central Heating System

A central heating system that is closed off from the mains or external water supply. The majority of new heating systems are designed this way as it aids the prevention of water oxidisation.

Cold Water Storage Tank

Usually located in a loft, but can be found anywhere that is higher than the system – (see Feed & Expansion Tank)

Combination (Combi) Boiler

A boiler that supplies both instantaneous hot water and central heating from the same appliance.


A chemical reaction in which a substance (a fuel) reacts violently with oxygen to produce heat and light.

Combustion Air

Air that provides the necessary amount of oxygen to ensure clean and complete combustion of a fuel, helping to maximise heating value.

Combustion Chamber

Any space – wholly or partially enclosed – within which combustion takes place.


The reduction of volume of a vapour or a gas by mechanical means.


This is what your boiler can become if it gets to a point that renders it beyond repair – a heating engineer will normally be the one to make this decision.


This is what you may sometimes find on the inside of your windows at home or in your car. It occurs when water reaches its dew point – or condensation point – at which point air turns from vapour to a liquid due to changes in temperature and pressure.

Condensing Boiler

A boiler that extracts all usable heat from the combustion process, cooling the flue gases – the collected water is then evacuated from the boiler form the condensate pipe.


Heat travelling through a substance with the heat being transferred from one molecule to another.


The property that enables a metal to carry heat (thermal conductivity) or electricity (electrical conductivity).


A type and style of interior decorating that contains the very latest style and trends, to help create an updated and modern look.


Heat transfer through the movement of a fluid substance – this could be water or air.

Convector Radiator

A radiator that transfers its heat via convection. These will normally have ‘fins’ at the back of the radiator or in between the radiators’ panels.


Any process involving the deterioration or degradation of metal components.

Corrosion Inhibitor

A chemical inhibitor that protects the inner workings of your heating system (See also Rust Inhibitor and Inhibitor).


There are two types of cylinders. A cylinder may be an ‘open vented’ type or an ‘unvented’ type. Vented cylinders have a vent pipe which will subject them to atmospheric pressure, whereas an unvented water cylinder is plumbed directly from the mains water supply. Unvented cylinders have many safety features in place to prevent excessive pressure build up and hot water expansion.

Damp-proof Course

A layer of impervious material that helps to prevent moisture from rising through a floor or through a wall.


Is the measurement in which heat output (see BTU) is measured. The temperature of the room is compared against the internal temperature of the radiator.

Designer Radiator

Any radiator that looks brilliant and has been designed to make a statement – readily available at Best Heating!


A direct unvented cylinder is one that is heated ‘directly’ from an immersion heater which is connected to the mains electrical supply. See also – Indirect.

Domestic Hot Water

Water that has been heated for residential washing or bathing, etc.

Double Glazing

Double glazed windows have two layers (panes) of glass separated by an air space. This air is designed to trap heat, increasing the windows efficiency and ability to prevent heat loss.

Drain Down

This is the process in which you remove all of the water from your central heating radiators. Isolating the boiler, opening the bleed valves and removing the water from the system. You may need to do this to install a new radiator or to flush the system (see power flush).

Draw off

The capacity output of useful hot water that is possible to extract from a hot water cylinder before the cylinder supply is depleted.

Dual Fuel

These are typically towel rails that can operate as part of the central heating or independently as a stand-alone heat source. Connected by a ‘T-piece’, this type of radiator is great for heating a single space in the summer, when you wouldn’t normally use your central heating.


A round or sometimes rectangular tube that distributes the exhaust fumes from your boiler.

Economy Seven

A UK tariff that provides seven hours of cheaper electricity, normally between the hours of 1am and 8am in the summer months and 12am and 7am in winter (Times are subject to variation dependent upon supplier and region).


This is the ratio of the useful work performed by a machine or a process to the total energy expended in that process – eg – this boiler has an efficiency of 45%.

Efficiency Class

The ErP directive is EU legislation which requires space and water heaters to be labelled with an energy efficiency class. This is scaled from A+++ (the most efficient) to G, which is the least efficient. September 2015 saw all products that didn’t achieve an E rating or above be banned from sale.

Electrical Heating Element

Inserted into an electric or dual fuel radiator allowing that radiator to operate independently of the central heating system.

Electricity Grid

The common term for the system that transmits and distributes electrical energy.


An electrolyte is a material that produces an electrically conducting solution when dissolved in a polar solvent, such as water.


A substance or a range of substances or pollutants that are emitted as a result of a process, such as combustion


The ratio, or total, of the energy (heat) being emitted by a surface, such as a radiator or a heated towel rail.


All radiators and heated towel rails that go on sale in the UK have to conform to certain standards and have their outputs verified to BS-EN442 – the European standard for all radiators.


The ability, or capability, of doing work – various forms of energy can be converted into other forms, but the total amount of energy always remains the same.

Energy Savings Trust

An independent non-profit organisation set up in 1992 with the express goal of reducing energy use in the UK.


All and every natural or living thing around you. The earth, air, weather, plants and animals and everything in between, each make up our environment.

Erosion Corrosion

Corrosion that occurs in tubes and fittings because of the fast flowing effects of fluids and gases.

ErP Directive

ErP stands for Energy-related Products. ErP is an EU directive to improve energy efficiency and performance standards of products.


When water is heated to 100°C it can expand by up to 4% of its volume at room temperature. Water heated above this temperature will turn to steam and can be extremely dangerous. This is why products such as hot water cylinders and electric water heaters are fitted with safety devices such as expansion vessels and temperature and pressure release valves.

Expansion Vessel

A vessel divided by a membrane that has air on one side and water on the other, allowing the expansion of water to take place safely.


A device that circulates or moves air in order to provide ventilation to a room, building or component.

Fan assisted boiler

A boiler that use a fan to evacuate the products of combustion.

Feed and expansion tank

Used to feed a vented central heating system and also allows expansion of water into the tank when the water is hot.

Filling Loop

A (usually) silver coloured flexible braided pipe connected to the bottom of the boiler, with a small valve at each end. Normally under the boiler, but sometimes incorporated into it.


A thin sheet of material – usually metal – that conducts heat. You will find these in various convector radiators.


A Fin is also a stylish designer radiator from Hudson Reed.


The last piece of any exterior surface such as a building, room, radiator or towel rail, and the process of applying it.

First Law of Thermodynamics

This law states that energy cannot be created or destroyed, but only changed from one form to another. It is sometimes known as the law of conservation of energy.

Floor space

The interior of a building, the area of which can be calculated in square feet and inches or metres.

Floor to Centre of Inlet

As you may assume, this is the distance between the floor and the centre of the valve inlet of your radiator.


A middle connection radiator from the home heating specialists Milano. This radiator allows you to hide away pipework with centrally located valve inlets; making for a sleek and modern finish to your heating.

Flow and Return

In central heating terms this is where the water flows into one side of a radiator or heated towel rail and flows out of the other, returning to the boiler to be reheated.

Flow rate

The amount of fluid or gas that flows through a pipe or a tube over a given time.


Aduct for smoke, steam or other waste gases produced by fires, gas heaters, boilers or other fuel-burning installations to vent through.

Flue Gas

This is the gas that is emitted as a result of the combustion of the fuel being burned in your system, as you might expect, it is emitted from the flue.


A paste used to clean oxides from the surface of copper and to help with the flow of solder into the fitting.


A material that can be burned to make or release energy.

Fuel Poverty

A household is said to be in ‘fuel poverty’ if they have required fuel costs that are above the (national) average and if they were to spend that amount, that they would be left with residual income below the (official) poverty line.

Fully Pumped Heating System

A heating system where both hot water circulation and central heating are both pumped by a central heating circulator.


A combustion appliance used to heat a home in which heat is captured from the combustion of fuel for distribution around a heating system. It will comprise mainly of a combustion chamber and heat exchanger.

Galvanic Corrosion

Corrosion that occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte, normally water.


A material that is galvanised is covered with a protective coating of zinc.

Gas Safety (Installation and Use) Regulations 1998

These regulations cover the safe installation, maintenance and use of gas appliances in private dwellings and business premises. The regulations are aimed at improving safety and preventing carbon monoxide (CO) poisoning, fires and explosions.

Geothermal Energy

Energy produced by the internal heat processes of the earth. It can be used for the purposes of heating or to help produce electrical power.

Global Warming

A term that is used to describe the apparent increase in the average temperature around the globe due to the effects of greenhouse gases in the atmosphere.

Gravity Feed Boilers

A solid fuel boiler in which fuel is automatically fed to the fire bed via gravity.

Greenhouse Effect

A term used to describe the effect of heating caused by the trapping of long wave radiation from greenhouse gases produced from human and other resources.

Greenhouse Gases

These are gases such as water vapour, carbon dioxide (CO2), methane and low level ozone, each of which are transparent to solar radiator, but opaque to long wave radiation – contributing to the greenhouse effect (see above).

Green Power

A well-known and popular term for any energy produced from clean, renewable energy resources.


A term used to refer to the system that distributes and transmits electricity.

Header Tank

This is just another name for a cold water storage tank or feed and expansion tank. Found in the loft, it’s used to hold the water that feeds into a home’s water system.


Thermal energy produced from the results of combustion, chemical reactions, and movement of electricity or friction.

Heat Exchanger

A device or vessel that allows heat to be transferred from one water system to another without the two ever coming into contact with one another. The transfer of heat takes place via conduction.

Heated Towel Rail

A small type of radiator usually installed in a bathroom or ensuite, that is used to hold towels and keep them dry until you need to use them. Larger installations of this type may also feature a high enough heat output in order for them to adequately heat the room.

Heating Calculations

These are done to calculate the heat requirements of your room. Use our BTU Calculator to determine what level of output you will need to adequately heat your space.

Heating Fuels

Any gas, liquid or solid fuel that is used for indoor space heating.

Heating Element

Used with radiator and heated towel rails to provide the source of heat, independently from the central heating system.

Heat Loss

Often used as a comparison between manufacturers, the heat loss figures are a measure of the amount of stored heat that escapes from an appliance, such as a water heater or a hot water cylinder over a period of time. The heat loss figures are a measure of the kilowatt hours lost over a 24 hour period.

Heat Output

This is the level of heat given off by a radiator or heated towel rail. It is measured in both BTUs and Watts and gives you an indication of whether the device will adequately heat your space or not.

Heat Pumps

An electrical device with reversible heating and cooling capability. It will extract the heat from one medium at a low temperature (the source of the heat) and transfer it to another at a high temperature, cooling the first and warming the second.

Heat Recovery

This is the transfer and then re-use of heat that may have otherwise been lost in the atmosphere. This could be heat that has been discharged from waste water – after you’ve had a bath or a shower – or simply recycling the heat from warm air through ventilation to outdoors.

Heat Transfer

The transfer of heat from one area to another by means of conduction, convection or radiator. Heat will flow naturally from a warmer area to a cooler material or space.

Heating, Ventilation & Air Conditioning (HVAC)

Heating, ventilation and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality.

Horizontal Designer Radiator

A fresh take on a standard radiator, a horizontal designer radiator will instantly add a sleek designer touch to your home. Easy to fit, stunning to look at, you couldn’t really ask for more.

Hudson Reed

Luxury bathroom and heating supplier, synonymous with quality, comfort and reliability.


To heat a mixture of gaseous substances to a temperature at which point combustion begins to take place.

Ignition Point

The minimum level of temperature required at which point ignition and combustion of a solid or fluid fuel can begin to occur.

Immersion Heater

A hot water heater that uses an electrical heating element to heat the water. It is controlled by a thermostat.


This is added to the fluid inside your central heating system to help against corrosion and protect the inner workings of your central heating (see also Rust Inhibitor).


An indirect unvented cylinder is one that is heated ‘indirectly’ via pipework running from the boiler. This is an incredibly efficient way of heating water and can be used to heat the home at the same time, meaning the boiler is carrying out two separate tasks at once.

Infrared Radiation

Invisible lon wavelength radiator (heat) capable of producing a thermal effect.


A heating installer should be a person that is suitably qualified, experienced and assessed as being a truly competent individual to carry out fitting, commissioning, maintenance and servicing of a heating system.

Instantaneous Hot Water System

A system of hot water supply that heats cold water directly from the cold water main, via a heat exchanger.


Insulation can be any material that is used to reduce the transmission of heat. This could be around windows and doors or in a loft, and is also any non0conductive material that is placed around electrical wires to prevent the passage of electricity.

IP Rating

This is an international classification system that classifies the effectiveness of an electrical components resistance to moisture and how well sealed it is from foreign bodies, such as tools, dust and fingers, etc.

Isolating/Isolation Valve

A valve used to shut off water from a particular room or appliance, used so you don’t need to turn off the entire water system.

ISO 9000

A set of international standards on quality management and quality assurance developed to help companies effectively document the quality system elements to be implemented to maintain an efficient quality system. They are not specific to any one industry and can be applied to organizations of any size.

Integrated Heating System

A type of heating device or appliance that performs more than just a single function, for example space and water heating.


Enclosure normally wrapped around a water heater, furnace or boiler.


A designer radiator with a chic and modern tubular design that will instantly inject some sleek contemporary style to any space. From heating specialists Milano.


A horizontal wooden or metal beam that is used to support a structure such as a floor, ceiling or a wall. It is often joists that plumbing pipework is attached to as it makes its way around your home.


A unit of energy, one joule (1J) is equal to the energy transferred or work done to an object when one Newton acts on that object in the direction of its motion through a distance of one metre – ie, 1 Newton Metre. It is also the amount of energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for a single second.

Kilowatt (KW)

A kilowatt is a measure of one thousand watts of electrical power.


A measure or a unit of electrical supply of 1000 Watts taken over a period of one hour. It is the equivalent of 3412 BTUs (See BTU).

Kinetic Energy

Energy that is available as a result of motion. The total amount of kinetic energy produced by an object varies in direct proportion to its mass and the square of the object’s velocity.

Law(s) of Thermodynamics

From your GCSE Science, the first law states that energy can’t be destroyed or created, the second states that when an exchange of heat occurs between two materials, the heat will always move from the warmer to the cool material.


A law or a group of laws that have come into force. Health and Safety legislation for the plumbing and heating industry includes the Health and Safety at Work Act and the Electricity at work Regulations.


When your pipework is perfectly horizontal.

Liquefied Petroleum Gas (LPG)

LPG is a mixture of gaseous hydrocarbons that are produced from natural gas, oil extraction and the refinery of that oil. It is an associated gas, so is therefore generated automatically during the production of methane in the refining process.

Locking Out

A process by which a thermostat protects the boiler from overheating by shutting it down when a temperature of around 85°C is reached.

Lockshield Valve

The lockshield valve is the valve on your radiator that is usually covered by a plastic cap. The term ‘lockshield’ means that once adjusted, the valve is shielded with the plastic cap to prevent it from being accidentally changed – in essence, locked.

Long-wave Radiation

Infrared or radiant heat.

Losses (Energy)

A general term that is used to refer to any energy that is converted to a form that is unusable. This energy is considered lost during the operation of an energy producing, consuming or conducting system.

Low Emissivity Windows

These are energy efficient windows that are applied with a thin coating or a film on the surface of the glass in order to reduce heat transfer through the surface of the window.

Low Pressure, Open-vented Central Heating Systems

Acentral heating system that is fed by a feed and expansion tank and contains an open vent pipe.

Low Surface Temperature (LST) Radiator

A radiator designed to offer the user full heat output whilst remaining cool to the touch.

Low Water Content Boiler

A boiler that contains only a small amount of water for quick water heating.

Manual Valves

Manual valves simply act like taps as they directly control the flow of water into the radiator and consequently how hot the radiator will get.


This is the material that buildings are made from, such as rock, brick or stone for example.

Mean Water Temperature

Mean water temperature is the average (mean) temperature of the flow and return water into the radiator (or across the heating or cooling system). Mean water temperature is calculated by adding the flow temperature to the return temperature and dividing it by 2.


A Megawatt is the term given to the measurement of one thousand kilowatts, or a million watts.


A MET is an approximate measurement of the heat or energy produced by a human being at rest – it is equal to about 18 BTUs per square foot per hour.


A display that enables gas and electric companies to take readings in order to send you an accurate bill for the energy that you have consumed in your home.


This is the main constituent of the gas that comes into your home. It is colourless, tasteless and has no smell (yes they do add the smell). It can be found naturally or made by man, to be used as a fuel or for making a variety of chemicals.

Micro Bore System

This is a central heating system with smaller pipework. Standard fittings have 15mm pipework, whereas a Micro Bore System features 10mm pipes.

Milano Heating

Specialist radiator designers and manufacturers, producing some of the most attractive and up-to-date designs in home heating. We love them!

Middle Connection

(See also central connection) This is a type of radiator valve inlet on the Milano Flow collection of designer radiators. Designed to help you hide away pipework and create a sleek modern finish to your home’s heating.


A motor can be any machine that is supplied with an external energy that is then transferred or converted into a force, function or motion.

Motor Speed

You’ll recognise this form your car or motorbike. It’s the number of revolution that your motor makes in a given amount of time, otherwise known as RPM – revolutions per minute.

Name Plate

Located on the outer surface of a machine or heating appliance, it should contain useful consumer information like brand name, serial number, a selection of power ratings and various other manufacturers’ information.

National Grid

The network of high voltage cables that carry electricity around the country.

Natural Gas

A light hydrocarbon fuel found naturally where oil and coal have formed. Natural gas predominantly contains five gases – methane, ethane, butane, propane and nitrogen.

Nitrogen Dioxide

A compound of nitrogen and oxygen that is formed by the oxidation of nitric oxide (NO) that is produced by the heating or combustion of solid heat fuels.


A horizontal timber used to reinforce non-structural walls. They are placed between vertical studs in a partition wall.

Non-ferrous Metal

Any metal that does not contain iron.

Non-renewable Fuels

Any fuel that cannot be easily manufactured or renewed, fuels like oil, coal and natural gas.

Non-return Valve

A non-return valve allows a medium or a fluid (liquid or gas) to flow through it, but only in one direction.

Occupied Space

The area within your home, office or any other building or structure that is normally occupied by people and that can be ‘conditioned’ to suit the occupants, ie – heated, ventilated or cooled.


The period within which energy is at its lowest demand (see also Economy Seven).


The unit of electrical resistance.

Oil (fuel)

A product of what is known as crude oil, it is used in the process of heating space and power generation.


Specified by the supplier of the fuel, this is the period in which energy – gas, electric, etc – is at its highest demand.

Open Flue

A flue that is open to the room in which the appliance is fitted. It relies upon the heat from the combustion process to create an updraught to safely evacuate the products of combustion.

Open-vented Central Heating System

Systems fed by a feed and expansion tank in the roof space that contains a vent pipe, which is not open to the atmosphere.

Open-vented Direct Hot Water Storage System

A hot water storage system containing a direct cylinder.

Open-vented Hot Water System

A system fed from a tank in the roof space (loft) that contains a vent pipe that is open to the atmosphere.

Open-vented Indirect Hot Water Storage System

A hot water storage system that contains an indirect type cylinder.


A gasket or seal in the form of a ring with a circular cross section, typically made from rubber. One of the simplest and yet most important precision mechanical developments ever made.


When the design capacity has been exceeded this is known as an ‘overload’.

Panel Radiator

A usually flat surface that is used to transmit radiant heat.

Part P

Part P governs the safety of electrical devices and appliances, ensuring that the correctly qualified people are responsible for the operation and maintenance of electrical installations and that any alterations are done by a professional, both safely and to a required standard.


A highly compacted source of solid fuels. Made primarily from wood sawdust that has been put under high pressure, pellets look a little like dry dog food and are burned in a pellet stove.

Pellet Stove

A more efficient, cleaner burning and easier to operate space heating device than other conventional wood burners, a pellet stove burns the pellets mentioned above.

Pilot Hole

A hole that is small in diameter, made with a drill and used to act as a guide for a screw thread.

Pilot Light

This is the small gas flame you can usually see through the little window in your boiler. It serves as a source of ignition for a more powerful gas burner.

Pipe Centres

This is the distance between the tappings on any radiator or heated towel rail. Plumb – When your pipework is perfectly vertical.

Pressure (Water)

Static water pressure is the pressure shown anywhere on the water supply piping system when none of your plumbing fixtures are in operation. Dynamic water pressure is the pressure shown anywhere on the water supply piping system when you have one or more plumbing fixtures in operation. The more you have running, the lower you can expect your dynamic water pressure to be.

Pressure Drop

The loss in static pressure of a gas or liquid in a heating system. This can be caused by friction from obstructions in pipes, problems with valves, fittings or burners, or may have been caused by a rupture in the system, like a burst pipe.

Pressure relief valve

A safety valve that safeguards against over-pressurisation by allowing excess water pressure to safely drain away.

Primary Circuit

The primary circuity is an assembly of pipework and water fittings within which water circulates between a boiler or other source of heat and a primary heat exchange inside a hot water cylinder.

Programmable Thermostat

This kind of thermostat allows the user to pre-program their heating devices to operating at a pre-set schedule of times – like when the temperature drops below a certain level, or when you arrive home from work.


Tape made from a material called polytetrafluorethylene, it is used to seal threaded plumbing fittings like radiator valves and elements.


Quad – One quadrillion BTU

That’s 1,000,000,000,000,000 BTUs – you’d need a fair number of radiators to achieve this number though.


A fixed price for a job, which cannot vary.

Radiant Barrier

This can be placed behind your radiator to block the heat and prevent it from being lost into a wall, or installed in your attic, loft or roof space to block radiant heat transfer.

Radiant Energy

This is any energy that transmits itself away from its source in any and all directions.


Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating – hot water or steam is delivered to a radiator by natural convection or by a pump in your boiler.

Radiator Key

(See also Bleed Key) Though you can use a flat head screwdriver with more modern radiators, you will need a radiator (or bleed) key to release air from your radiators when the need arises.


Heat transfer as thermal radiation from infrared light, visible or not, which transfers heat from one body to another without heating the space in between, travelling in straight lines.


A European wide colour matching system that allows you to choose the correct colour of radiators.

Rated Power

The output of a device when it is placed under any specific operating conditions.


The reworking process of converting materials that are no longer of any use – meaning they cannot complete the job they were designed for or intended to do. Recycling is the process of repurposing these materials into a new product.


A piece of kit that is designed to reduce the size of a connection, sometimes known as the ‘end-bush’.


Put simply, this is the concept of just how long a device or a process can continue to operate, without the need for maintenance or replacement of parts or the unit as a whole.


A natural source or resource of energy that is not depleted by use, such as water, wind or solar power.


The act of repurposing a building or the process of modifying its structure.


The return water that comes from within your central heating system.

Reversed Central Heating Return System

A central heating system where the return travels away from the boiler in the same direction as the flow, before looping around to be connected to the return at the boiler.

Rising Main or Riser

A pipe that supplies water under mains pressure, usually into a roof storage tank.

Risk Assessment

This is an assessment or test undertaken by a detail contractor investigating the health, safety and any risks associated with a particular contract.

Rust Inhibitor

(See also Inhibitor) A solution that can be added to your central heating to help prevent corrosion of the metal in your radiators and towel rails.


This is damage caused by the build-up of lime-scale in your central heating appliances and pipework. Left unchecked, scale can destroy components and create untold damage that can be very expensive to remedy.

Sealed Combustion Heating System

A heating system that uses air from outside for combustion and one that vents those exhaust fumes to the outdoors.

Sealed Central Heating System

A central heating system fed direct from the cold water main and incorporating an expansion vessel.

Second Law of Thermodynamics

This is an absolute law, stating that no device can ever completely and continuously transform all of the energy supplied to it into useful, or usable, energy.


The Seasonal Efficiency of Domestic Boilers in the United Kingdom. This has largely been replaced by the ErP Directive, but may still be seen and used by some installers. In heating terms, it’s effectively a list of boiler efficiency ratings.

Secondary Return

A type of plumbing system used in both commercial and residential water heating systems, it is designed to ensure that hot water is always available at every point of use. It basically ensures that when you are running a bath upstairs, someone can be downstairs doing the washing up.

Single Glaze or Pane

A thin pane of glass that provides a barrier to the outside world. These have very little insulating value and can be the cause of considerable heat loss in the home.

Single Heat

This is where a temperature has been pre-set to remain and regulate at the same setting.


A high-performance designer radiator from Hudson Reed that brings together practicality and style into one package.

Solar Collector

Used with solar hot water heating, the solar collector collects the sun’s warmth and transfers it, through a heat exchanger, to the hot water storage vessel.

Solar Thermal

Technology that utilises the heat from the sun to generate a domestic hot water supply.

Solid Fuel

Any and all fuels that are available in a solid state – such as wood, peat, coal and other manufactured fuels like coke, charcoal, briquettes and pellets for example.

Space Heater

Simply a movable or static fixed heater – like a portable radiator – that can be moved around to heat individual spaces.


Another name for the plain end of a pipe. If you buy a fitting with a plain pipe end, this is usually called a ‘spigot end’.

Stab (the pipes)

This is one for all you plumbers and heat engineers out there. It’s a term used by them when they ‘stab’ the pipes through the floor or the wall in readiness for a radiator to be fitted.

Standing Loss

A measurement of the heat that escapes from a hot water cylinder through the high radiating areas of the casing, such as the immersion heater. This heat loss is commonly referred to as standing loss and is measured in kilowatt hours (kWh) lost over 24 hours.


This is a flue (see above) for exhausting or venting the products of any combustion from appliances like a boiler.


Steam is just water in vapour form and is often used as the operating fluid in many heating systems.


A type of ball valve used to control the flow of a liquid or gas; like a water main for example.

Storage Tank

Simply the tank of a water heater.

Storage Water Heater

A device that releases hot water from the top of a tank whenever a hot tap is turned on (opened). To ensure that the tank remains full, cold water will enter the bottom of the tank to replace the hot water that is used.

Straight Valves

Used when pipework is coming out of the floor, these straight valves for use on radiators.


The strainer is a pipework connection that is placed on the cold water main that comes into your property. It is designed to filter out any particles that may come in with the cold water system, and because of the sensitive nature of some of the components, a strainer will help to keep them clear of grit and other foreign bodies.

Stud Partition

A timber framed interior dividing wall.

Supplementary Heat

A separate heat source, such as a space heater (see above) that is used to provide additional heat than that which is provided by a primary heat source.

System Boiler

A central heating boiler that contains an expansion vessel and pressure relief valve in a single unit.

TBOE or Top Bottom Opposite Ends

This is when radiator flow valves are placed on the top of one side of a radiator and the lockshield valve is installed at the bottom on the other side.

TBSE or Top Bottom Same Ends

Flow valves at the top and lockshield valve at the bottom on the same side of the radiator (as you would expect).

T-Piece or T-pipe

Used in a dual fuel heating system to allow a valve and an electrical heating element to be fitted at the same point of entry.


The copper pipes that are fitted to a radiator or towel rail.

Tankless Water Heater

Also known as a demand water heater, a tankless water heater warms water before it is directly distributed when required.


This is the thread in the inlets of a designer radiator or heated towel rail in which the valves or elements will be screwed.

Temperature and Pressure Relief Valve (T&P Valve)

This is a safety device to relieve pressure from a hot water cylinder when they reach extremes. As water begins to heat up, it expands, the T&P valve will protect your cylinder by discharging water through the waste pipework when the cylinder pressure and temperature reaches excessive levels.

Tensile Strength

A measure of how well or badly a material reacts to being pulled or stretched until it breaks.


A study of the transformation of energy from one distinct form to another, and how this can be applied in a practical setting.


A thermostat is a device that automatically regulates temperature, or that activates a device when the temperature reaches a certain point.

Thermostatic Radiator Valve (TRV)

A radiator valve that opens and closes automatically to help to maintain a set temperature.


A device that can be programmed to automatically turn appliances on and off at set times.

Towel Radiator

This is a rad that has been designed specifically with job of warming towels in mind – often used in cloakrooms, bathrooms, kitchens and ensuites.

Towel Rail

In the not too distant past , this was simply a rail for hanging towels on, now however, it means pretty much the same thing as towel radiator (see also Heated Towel Rail).

Triple Pane

A step up from double glazing, triple panes feature three layers of glazing in a window, with an air space in between the interior and exterior sheets of glass.

Turn Down Ratio

Not something you’ll hear too much about, but this is the ratio of a boilers maximum output to its lowest output.

Two-pipe Central Heating System

A system having two pipes, a flow and a return, which are connected to the boiler.

Type 11

This is a type of convector radiator that features one radiator panel and a single set of convection fins.

Type 21

As Type 11 but with 2 radiator panels and a single set of convection fins.

Type 22

A type of radiator with 2 radiator panels and 2 sets of convection fins.

Underfloor Heating

A method of using concealed underfloor pipework to warm a dwelling. It’s a little like turning your entire floor into one big radiator!

Units of Power

These are read as kWh (kilowatts per hour).

Unvented Heater

Featuring an oxygen sensor that will shut the appliance off when oxygen levels fall below a safe level, an unvented heater is a combustion heating appliance that releases (vents) the by-products directly into a heated space.

Unvented Hot Water Storage Systems

Systems fed directly from the cold water main that are not open to the atmosphere and contain an expansion vessel expansion or expansion bubble.

Utilities (utility)

Utilities is the term given to the set of services that are consumed by the public – electricity, natural gas and water are the ones associated with heating.

Variable Heat

Whereby the temperature can be manually controlled to reach a desired temperature.


A vent is used to disperse or conduct fresh air in, or waste air and gases out of an interior space or appliance.


The process of air being moved out of an interior space by natural or mechanical means.

Vertical Designer Radiator

A stylish and contemporary home heating device with a height of a greater distance than its width. An unconventional though yet highly popular way in which to heat a space.


Another classic designer radiator from Milano, the Viti features uniquely styled diamond panels that add a sense of style to any space and are an instant designer pick-me-up for your home heating.


Not to sound all technical, but a volt is a unit of electrical force that is equal to the amount of electromotive force that causes a steady one-ampere current to flow through a resistance of one ohm (see above).


You know, a wall? A vertical structural element that forms part of a room, is used to hold up a roof or stands by itself to hold back earth.

Wall to Centre of Inlet

The overall distance from the wall to the centre of the tapping.

Water Jacket

This is a heat exchanger element that is housed or enclosed inside a boiler. Water is then circulated through the jacket by a pump, it is then heated up by residual heat from the combustion chamber and is then distributed to a variety of distributers – like radiators for example.

Water Main

A water main is the principal or ‘main’ pipe that delivers water into a customer’s service pipe.

Water Service Pipe

The primary pipe into a property from the water main.

Water Source Heat Pump

A kind of heat pump (geothermal) that uses water from the ground, or surface, as a source of heat. This is a very efficient way to heat things as water tends to have a more stable seasonal temperature than air.


Technical jargon time again. A Watt is the rate of energy transfer that is equivalent to one ampere under an electrical pressure of one volt (see above).


The unit of electricity consumption by one Watt over a period of 60 minutes (an hour).


A measuring device used to calculate the consumption of power.


A stylish and captivating designer radiator from Milano Heating. The Wave will make a stunning visual impact in any space.


You’ll know this one – a term used for the glass opening that lets daylight into a home or office, they can also be opened to aid ventilation.


The Windsor is Milano Heating’s take on the classically styled cast iron radiator – a contemporary take on a period classic for the traditionalists out there.


An electrical conductor, mostly made of copper.

Wood Stove

Nope, not a stove made of wood, a wood-burning appliance that can be used to heat a space or water tank or used in the cooking process.

Working fluid

This is the name given to a fluid that can be used to transfer or absorb heat energy.

Working Pressure

The very maximum operating pressure of a heating system.

Wrought Copper Fittings

Made form mechanically worked and toughened copper, wrought copper fittings are used to connect copper piping.


An unusual and distinctive designer radiator from Hudson Reed.

Yellow Tipping

This is a condition of the flame in your boiler and is caused by a severe reduction in air flow. The yellowing of the flame is caused by carbon particles glowing and can be rectified by a sharp injection of primary air.

Zero Carbon Fuel

Any fuel with which the net carbon dioxide emissions from all of the fuel used is zero, zilch, not a sausage.


Any area within the interior of a building that is to be cooled, heated or ventilated.

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