If you’re confused by heating terms such as ‘ErP rating’, ‘sealed system’ or ‘Power flush’ – don’t worry, you’re not alone! When it comes to central heating, there’s a lot of jargon out there.
So, we’ve put together this A-Z glossary of key terms that will help you to understand the lingo.
Heating jargon – A is for…
You’ll often see engineers describing themselves as ‘Accredited Installers’ of a particular brand of boiler. This means that the engineer has completed additional training so that they can advise on and install a particular manufacturer’s boilers to the highest possible standard. We are:
- Accredited Heat Geek installers
- Worcester Bosch Accredited Installers
- Vaillant Advance Installers
- Viessmann Trained Installers
- ATAG Selected Partners
Air source heat pump
Air source heat pumps (ASHPs) absorb heat from the outside air to heat your home and hot water. Therefore, they are a cheaper and more environmentally friendly way of heating your home.
This is is often used to refer to the ordinary or baseline temperature of a room. A lot of people think that ideal room temperature is 21 °C. But the best room temperature for your home is a steady 18 °C or 19 °C. By turning your thermostat down even by just a single degree, you’ll see some significant savings on your energy bills.
An annual service is where a Gas Safe engineer will conduct various tests on your boiler to make sure that it’s functioning safely and effectively. A bit like an MOT for a car, a boiler service is vital maintenance for your central heating system. So, don’t forget to book yours!
ATAG manufactures boilers that offer outstanding engineering, reliability, and energy efficiency. As ATAG Selected Partners, we can offer extended guarantees of up to 14 years on ATAG boilers. Consequently, you’ll have peace of mind that your ATAG boiler will stand the test of time!
B is for…
This is where a loss of system pressure is causing water to flow in the wrong direction.
Balancing your heating system
Balancing your heating system means optimising the flow of water in your heating system, so that all of your radiators heat up evenly and give off the right amount of heat.
In unbalanced systems, some radiators (probably the ones closest to your boiler) take the bulk of the hot water flow, leaving other radiators with less. This can reduce your boiler’s efficiency and leave you with some rooms that feel warmer than others.
The idea is to get the water returning to your boiler to be 50 degrees or lower, so that your boiler can operate in its efficient condensing mode.
A bar is a metric measurement unit of pressure, relating to water, gas, or air. When the heating is on your boiler pressure should be between 1.5 and 2 bar. You can check this on your boiler’s pressure gauge.
This manufacturer of boilers has some of the best known and trusted heating and hot water brands for residential and commercial heating customers in the UK and Ireland.
Benchmark is a universal ‘checklist’ that engineers follow when installing, commissioning, and servicing boilers. The HHIC created it to run alongside the Building Regulations in England and Wales.
Most boilers in the UK burn gas to produce heat. But a biomass boiler burns natural materials such as wood pellets, chips or logs to provide heating and hot water.
Bleeding a radiator
Bleeding a radiator means letting trapped air out of your heating system using a radiator bleed key. As a result, your boiler can heat your home more effectively and helps to reduce your energy bills.
Bleed keys release trapped air from your radiators (‘bleeding’ radiators). They loosen and tighten the square headed bleed screw located in the middle of the bleed plug at either the top left or top right of a radiator.
Bleed valves are usually found at the top of your radiator or heated towel rail. They allow you to expel trapped air from your heating system using the radiator bleed key.
Boilers use fuel to transfer heat to water to warm your home, and give you hot water for your baths and showers. There are three main types of boiler system on the market: combi boilers, system boilers and heat-only boilers.
Introduced in April 2018, these standards improve the way people use energy in their homes, giving them a greater choice on how to maximise energy efficiency. Boiler Plus requires that all boilers must be at least 92% efficient and all gas and oil boilers must have appropriate time and temperature controls fitted. Bolier Plus also requires that combi boilers have one of four additional energy saving devices fitted: FGHRS; weather compensation; load compensation; or smart controls with automation and optimisation functions.
The Building Regulations protect the health and safety of people in and around buildings. In addition, they improve the conservation of fuel and power, protect and enhance the environment and promote sustainable development.
C is for…
Carbon dioxide (CO2) is a gas which is naturally present in the air (about 0.03 per cent). Plants absorb it during photosynthesis. Unfortunately, humans produce carbon dioxide through activities that involve burning fossil fuels.
Carbon dioxide is a major component of greenhouse gas, responsible for global warming and climate change. Globally, heat accounts for nearly half of all energy consumption and 40% of energy-related carbon dioxide emissions.
Carbon monoxide is a poisonous gas, which has no smell or taste. Exposure to this gas will make you very unwell and can cause death. Therefore, it’s vital to have your boiler serviced every year by a Gas Safe engineer to keep it safe.
Your boiler’s casing is the surround that protects the inner workings of the boiler. Only Gas Safe engineers can remove these.
Celsius is a unit of temperature on the Celsius scale, a temperature scale originally known as the centigrade scale.
Your boiler burns fuel to heat water, which it pumps through pipes to your radiators and hot taps.
A cistern is another name for the header tank or feed and expansion tank. Its role is to supply water to the central heating system and maintain the level of water, which expands when heated.
Cold water storage tank
Used in open vented central heating systems to provide the system with mains cold water. They are usually located in a loft to allow gravity to feed the system.
Combination (combi) boiler
Combination boilers, or ‘combi’ boilers, provide heating and hot water from one compact unit, without the need for any external tanks or cylinders. Combi boilers are the most popular type of boiler sold in the UK.
Your boiler relies on the process of combustion to provide heat for your home and hot water for your baths and showers. Combustion is a chemical process in which the fuel reacts rapidly with oxygen and gives off heat.
It’s a legal requirement (under the Building Regulations) to have your boiler commissioned by a Gas Safe engineer. Your engineer will follow the boiler commissioning checklist provided by the HHIC. Thid avoids common boiler issues by ensuring your new boiler has been set up correctly.
Condemned boilers are not safe to use. There are two categories of condemned boiler. An ‘immediately dangerous’ boiler is one which if operated or left connected to the gas supply is an immediate danger to life or property. ‘At Risk’ boilers have at least one fault which could endanger life or the property.
When your boiler burns fuel to heat water for your heating system, condensation also forms. The boiler expels this as a gas. Some condensate collects inside the boiler and is drained away through the condensate pipe.
Condensation occurs when water reaches its dew point. Changes in temperature and pressure turn air from a vapour into a liquid. This will happen when your boiler burns a fuel (such as gas) to heat water.
A condensing boiler uses condensing technology to extract all usable heat from the combustion process. When a boiler burns gas to produce heat, it releases hot gasses through the flue into the atmosphere. Non-condensing boilers waste these gases. But condensing boilers capture the hot flue gasses and recycle them to help heat water in the system. Condensing boilers are therefore much more energy efficient than non-condensing boilers.
A conduit is a tube that houses electrical wiring.
Controls allow you to easily regulate the temperature of your home without wasting fuel or heat. There are a huge variety of heating controls available, including: time switches; programmers; room thermostats; programmable room thermostats; smart thermostats; and thermostatic radiator valves (TRVs).
Convection transfers heat is by the movement of a heated fluid such as air or water. It’s the process that your central heating system uses to transfer the heat from water to the rooms in your home.
Corrosion is the gradual deterioration and degradation of materials (usually a metal) by chemical and or electrochemical reaction with their environment. Unfortunately, if you don’t look after your central heating system, the insides of your pipes and radiators can degrade, requiring a Power flush or replacement.
A corrosion inihibitor can help to prolong the life of your central heating system by protecting your heating system against corrosion. You can protect the ineer workings of your heating system by using a chemical inhibitor during a power flush.
Boiler cycling is when a boiler turns on and off to maintain the desired temperature. Constant firing and shutting down wastes a lot of fuel and energy and takes its toll on your boiler.
Hot water cylinders (used by heat-only and system boilers) hold your hot water until its required.
D is for…
Domestic hot water (DHW)
This is potable water that is safe for washing or bathing in your home.
Double glazed windows have two layers (panes) of glass separated by an air space. This air traps heat, increasing the windows efficiency and ability to prevent heat loss.
This is the process in which a Gas Safe engineer will remove all the water from your central heating system. This may be necessary when installing a new radiator or to power flush the system.
A round or sometimes rectangular tube that distributes the exhaust fumes from your boiler.
E is for…
Efficiency is the ratio of the useful work performed by your boiler to the total energy expended in that process. For example, for a modern boiler with 92% efficiency, 92% of the energy heats the home, and 8% is ‘lost’/used to run itself.
The ErP Directive requires that space and water heaters to be labelled with an efficiency class. Boilers, like other domestic appliances, have efficiency ratings of A-G, A being the most efficient to G which is the least efficient. For a very old boiler with 60% efficiency, only 60% of the energy used by the boiler goes to heating the home, whilst a huge 40% is wasted.
Processes such as combustion produce substances or pollutants called emissions.
Energy Savings Trust
An independent non-profit organisation set up in 1992 with the express goal of reducing energy use in the UK.
ErP stands for Energy-related Products. It relates to an EU Directive which drives improvements in the efficiency and performance of heating and hot water products across Europe.
A European Directive on ErP came into force in 2015 and replaced SEDBUK (Seasonable Efficiency for a Domestic Boiler UK). The ErP Directive covers boilers, combination boilers, water heaters and other heating appliances up to 400kW.
The ErP Directive (see above) rates the efficiency of all energy-consuming goods between A++ and G and you can usually find this on the casing of your boiler. All new boilers fitted into existing properties must have an ‘ErP’ (Energy rated performance) of 92%.
Expansion vessels keep the pressure in a combi boiler stable while water heats and cools. Water expands by up yto 4% of its volume at room temperature when its heated. So, the expansion vessel accommodates this.
F is for…
Feed and expansion tank
Open vented heating systems need feed and expansion tanks. Often located in the loft, they to up the central heating system with cold water as well as providing somewhere for the hot water to go if your system overheats.
The filling loop is a small, braided hose with connections on either end. It provides a temporary connection to the mains so that you’re able add additional water to your heating system.
Flow rate is the amount of fluid or gas that flows through a pipe or a tube over a given time. A boiler’s flow rate shows how much hot water it can send to your taps in one minute. But this will depend on the flow rate of the mains water supply to your home. If the flow rate of your mains is lower than the flow rate of the boiler, then it will never reach that level.
A flue is a duct, pipe, or chimney which takes exhaust gases from your boiler to the outdoors. Flues are essential to keep you safe because they take the products of combustion (which contain carbon monoxide and other noxious gases) out of your home, and release them into the atmosphere.
Burning fuel produces flue gases. The flue releases flue gases safely outside your home.
Flue Gas Heat Recovery Systems
Flue gas heat recovery systems make boilers more efficient by capturing and reusing heat energy that would otherwise have escaped out of your flue or chimney.
Any material (such as gas, oil or coal) that will react with other substances so that it releases energy as heat energy.
G is for…
Gas Safe Register
The Gas Safe register lists businesses that can safely and legally work on gas. It’s the only official gas registration body of the United Kingdom, the Isle of Man and Guernsey.The Gas Safe Register issues licenses for engineers to undertake gas work on behalf of a registered business if they have evidenced competence through a valid and current qualification. We are Gas Safe registered.
Gas Safety (Installation and use) (Amendment) Regulations 2018
These regulations came into force on 6 April 2018 and cover the safe installation, maintenance and use of gas appliances in private dwellings and business premises. The regulations improve safety and help to prevent carbon monoxide poisoning, fires, and explosions.
Green power is a subset of renewable energy and covers energy produced from solar, wind, geothermal, biomass, and low-impact small hydroelectric sources.
A term used to refer to the system that distributes and transmits electricity.
H is for…
Header tank is another name for a feed and expansion tank. Open vented systems usually have one in the loft. Its job is to supply water to the central heating system, and to maintain the level of water, which expands when heated.
A heat curve is a graph showing the relationship between the central heating system supply temperature and the outside air temperature. Weather compensation controls use them to ensure that the flow temperature of your boiler is matched to the actual heat demand.
Your boiler’s heat exchanger transfers heat from your fuel (usually gas) to the water. The boiler pumps the hot water around your home to heat your radiators and supply your hot taps.
Created to give expert advice on all aspects of the heating industry to both end users and industry professionals. The Heating People are proud to be Heat Geek Elite installers and Heat Geek Assured installers of heat pumps. This means we have undergone the best heating design training the industry has to offer!
Heat loss is a measure of the amount of heat escaping through your building’s fabric from the inside to the outside. All buildings lose heat, but the colder the outside temperature; the warmer the inside; and the worse the insulation of your building; the greater the heat loss will be. Reducing heat loss makes your heating system more efficient, reducing energy bills and your carbon footprint.
Also known as ‘conventional’ or ‘regular’ boilers, heat-only boilers provide heating directly to your central heating, and work with a cylinder to provide your hot water. They can be ‘open-vented’, meaning that there’s a feed and expansion tank in the loft, but they can also work on a ‘sealed’ system too.
Heat pumps are electrical devices that transfer heat from a source (such as the heat of the soil in the garden) to another location (like the hot water system of a house). Although they use a small amount of electricity, they are extremely efficient, with an efficiency rate of between 200-600%.
This recycles heat that would usually be lost into the atmosphere. It increases the efficiency of your heating system by reducing the heating and cooling demands. Modern condensing boilers will have some form of heat recovery built in, but additional Flue Gas Recovery Systems can further increase efficiency by recycling heat from waste flue gases.
Heat energy can be transferred by conduction, convection or radiation. Your central heating system generates heat by transforming the chemical energy in fuel (usually gas) into thermal energy. It transfers heat to water, which is pumped around your home.
Heating and Hotwater Industry Council (HHIC)
The HHIC is committed to effectively driving, supporting and promoting the sustained growth of the UK domestic heating and hot water industry.
I is for…
Ideal provides reliable, competitively priced boilers to all of its installers and consumers.
An immersion heater is an electric water heater that sits inside a hot-water cylinder. They use a metal loop or coil to heat the surrounding water. They can be the main source of hot water or provide a back-up for a traditional gas boiler.
To work on gas, a heating installer must be Gas Safe registered.
This is any material that reduces the transmission of heat (or sound) from one area to another. Insulation is important to reduce heat loss and improve the efficiency of your central heating system.
An isolation valve is part of a heating system that restricts or completely stops the flow of water through the system. Isolation valves are useful for fixing small issues like a dripping tap, because there is no need to turn off the mains water if one of these valves is installed.
J is for…
A joule is a unit of energy. One joule is equal to the work done by a force of one newton acting through one metre. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.
K is for…
Kilowatts measure the ‘size’, or the power output of a boiler. A kilowatt is equal to 1,000 watts and this unit helps us to measure the power your boiler can provide to your heating system. For example, a 25kW boiler uses 25,000 watts (25 kW) of power per hour to heat the water for your central heating. Generally, the more heat and hot water you require for your home, the higher the kW boiler you will need. But the type of boiler you have will affect this.
Kilowatt-hour (or kWh)
A Kilowatt-hour is the unit of energy utility companies use to measure how much gas and electricity you’re using. It refers to the use of power over a period – for example a 1 kW hair dryer used for an hour will use 1 kWh.
L is for…
Load compensation is an energy saving control that uses an internal temperature sensor to measure the difference between your current room temperature, and your desired room temperature, to control your boiler’s output to precisely close the gap.
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Approved Document L was introduced in October 2010 as part of the Building Regulations and was recently amended by Boiler Plus. Approved document L provides guidance on the conservation of fuel and power. Part L1A applies to newbuild homes and Part L1B which sets the standards for work carried out in existing homes, to achieve carbon reduction targets.
M is for…
Boiler modulation refers to the ability of a boiler to automatically reduce its output to suit the demand for heat, thereby lowering the amount of gas it’s using.
The modulation ‘ratio’ is how manufacturers express a boiler’s ability to modulate. The numbers refer to the boiler’s minimum output in relation to its maximum output. The wider the modulation range, the better the ratio.
N is for…
The National Grid is the system operator of Great Britain’s electricity and gas supply. This includes England, Scotland and Wales. It is the company that manages the network and distribution of electricity and gas that powers all our homes and businesses.
Gas is one of four fossil fuels (along with coal, sulphur and petroleum) that forms deep beneath the earth’s surface. It predominantly contains five gases – methane, ethane, butane, propane and nitrogen. The largest component of natural gas is methane. It is a non-renewable hydrocarbon used as a source of energy for heating, cooking, and electricity generation.
The Institute for Government says that net zero means “achieving a balance between the amount of greenhouse gas emissions produced and the amount removed from the atmosphere.” In other words, any greenhouse gas emissions that can’t be avoided must be matched by removing the equivalent from the atmosphere. For more on how the government intends to achieve this, check out our related blog here.
Nitrogen Dioxide (NO2) is a colorless, odorless gas that is commonly emitted when we burn fuels for our heating appliances (such as boilers and ovens).
A non-return valve allows a liquid or gas to flow through it, but only in one direction. The purpose of this is to ensure that the liquid or gas flows through a pipe in the right direction, where it might otherwise have unwanted reversed flow.
O is for…
OFTEC stands for the Oil Firing Technical Association. It recognises installers who are approved to install oil, solid fuel and renewable heating equipment and to main oil and solid fuel systems.
An open flue has a pipe which carries combustion gases from the appliance, whilst fresh air enters the appliance via the casing. For safe operation, additional air vents are required in the room where the appliance is installed to re-supply fresh air.
Open-vented central heating system
Heat-only boilers are sealed or open vented. Open vented heating systems are open to atmospheric pressure and have a feed and expansion tank at the highest point in the system. The water tank in the loft maintains the right water level whilst a pump circulates the hot water to your home’s radiators.
P is for…
PCB stands for printed circuit board. The PCB monitors your boiler’s pressure, temperatures and currents and controls the boiler electronically. Sometimes, it will develop a fault or stop working properly, or sometimes it may shut down the boiler because another component is not working properly.
The pilot light ignites the gas, which heats the water in your boiler and fires up your central heating.
Power flushing is a way of cleaning and maintaining your central heating system. Your engineer will use a power flushing machine to send water at high velocity through your heating system. This dislodges and removes debris, limescale, and sludge which can build-up over time.
This refers to the pressure of hot water running in your sealed central heating system, while water pressure is the pressure of the water coming through your taps.
Most modern (and some older) heating systems are sealed, and the system is pressurised to ‘push’ the water around your system. To work efficiently, it must maintain a stable pressure, which is determined by the volume of water in your heating system. If there is a pressure drop, your system can cut out, preventing your central heating from working. Re-pressurising your boiler will help to keep your boiler working well.
Pressure relief valve
Pressure relief valves are primarily used within sealed heating systems as a safety mechanism to release high pressure within the system. When the pressure gets too high, pressure relief valves open to reduce the pressure, and prevent damage to the system.
Programmable thermostats are thermostats which adjust the temperature according to a series of programmed settings that take effect at different times of the day. They allow you to pre-set your heating schedule, so that your heating comes on and switches off depending on when it’s required.
Tape made from a material called polytetrafluorethylene.
Q is for…
A quotation is a formal statement setting out the estimated cost for a particular job or service. We will provide you with a fixed price quotation after completing a survey of your home and requirements.
R is for…
Radiators are a vital part of your central heating system. Hot water from your boiler runs through the piping in your home, warming up each radiator in your system. When water in the radiator is hot, the surrounding air heats up via convection and the hot air moves around the room as the air circulates.
(See also Bleed Key) Radiator keys are hand tools for undoing, tightening, and adjusting the fittings of a central heating radiator.
A natural resource or source of energy that is not depleted by use, such as water, wind, or solar power.
Renewable energy comes from natural sources or processes that are constantly replenished and do not diminish over time. Such fuel sources include the sun, wind, moving water, organic plant, and waste material (biomass), and the earth’s heat (geothermal).
Individual room thermostats measure the temperature of the air in the room, if it is cold, it will tell the central heating to turn on, when it gets too warm it tells the central heating to turn off.
S is for…
Sealed heating system
A system that is closed to the atmosphere and does not have a feed and expansion tank. Instead of using a feed and expansion tank, a sealed system comprises an expansion vessel into which system water can expand as the water heats. As the system cools, this pressurised vessel pushes water back into the system.
An S Plan Heating System has two separate motorised valves which control the temperature of the central heating and the hot water individually.
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.
Steam is water in vapour form. It is the operating fluid in many heating systems.
A stopcock is a type of ball valve that controls the flow of a liquid or gas, like a water main for example.
Over time, the water in your pipes, boiler, and radiators deposits unwanted by-products like rust. This rust (plus other dirt and debris) becomes an unpleasant, muddy substance, known as ‘sludge’. This sludge plays havoc with the efficiency of your heating system, causing corrosion and blockages. Sometimes it can be removed with a power flush.
This refers to the short wave radiation from the sun that heats a building, either directly through an opening such as a window, or indirectly through the fabric of the building.
A solar thermal system uses the energy from the sun to heat up water to use in the home. Solar collectors absorb heat from the sun. The heated water or heat-transfer fluid then runs from the collectors to your hot water cylinder.
System boilers feature aspects of both a heat-only boiler and a combi. Like a heat-only boiler, a system boiler needs a hot-water cylinder to heat and store hot water for your taps. But it doesn’t need a tank in the attic because, like a combi, it takes its water supply directly from the mains. The heat exchanger heats the cold water by transferring energy from the gas jets to the water. The boiler pumps the water into a large hot water cylinder.
T is for…
Temperature and Pressure Relief Valve
A Temperature and pressure relief valve is a safety device to relieve pressure from a hot water cylinder when they reach extremes.
A thermostat is a device that automatically regulates temperature, or that activates a device when the temperature reaches a certain point.
This is a thermostat which is inside the boiler casing that limits 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.
TRV stands for thermostatic radiator valve. TRVs fit on the side of your radiator and allow you to control the heat output of a radiator and the temperature of a room. They can help you to save energy, and therefore money on your energy bills.
Timers or boiler time switches are the simplest type of heating control because they simply turn your boiler on and off at preset times. Time switches are generally not used on modern systems where more appropriate programmable thermostats or compensating control is used.
U is for…
Unvented cylinders store and heat water that is taken directly from the incoming mains supply. This is different to a vented cylinder, which is gravity fed by a tank in the loft. You can get hot water out of an unvented cylinder at a much better pressure than with a vented cylinder, because it is pressurised.
V is for…
Vaillant are one of the leading manufacturers of boilers, heat pumps and heating systems in the UK. The Heating People are proud to be Vaillant Advance Installers.
A vent is used to disperse or conduct fresh air in, or waste air and gases out of an interior space or appliance.
Vented cylinders store and heat water that is fed directly from a tank in the loft. They are sometimes referred to as gravity fed hot water systems. This is because the tank in the loft is higher than the vented cylinder, and the natural pull of gravity carries the water down from the tank to the cylinder.
The process of supplying a house or room continuously with fresh air.
The Viessmann Group is a German company specialising in heating, cooling, and refrigeration systems. The Heating People are proud to be Viessmann trained installers.
W is for…
Reputable boiler manufacturers will give you a warranty on a new boiler. This is a promise to repair or replace the boiler free of cost if necessary, within a specified period of time. The warranty covers the cost of repairs and maintenance and sometimes includes replacement parts and labour costs. The Heating People can offer warranties of up to 14 years on ATAG boilers.
A water main is the principal or ‘main’ pipe that delivers cold water into your home.
Water pressure determines the flow of water from the tap. Low pressure can reduce water flow to a trickle, and it will take a long time to fill a kettle or a cistern. Some modern heating appliances and showers will not work below certain pressure levels.
Weather compensation devices are heating controls. They use an outdoor sensor to monitor the outdoor temperature and adjust your boiler’s operation accordingly. By matching your home’s heat loss (which is caused by the weather) you can save on your energy bills, as well as reducing your carbon footprint.
Worcester Bosch are one of the market leading brands in the heating and hot water systems industry. The Heating People are proud to be Accredited Installers of Worcester Bosch systems.
X is for…
We were stumped with this one!
Y is for…
A Y-Plan heating system is a system that uses one motorised valve, which has 3 ports for water to flow through. ‘Y Plan’ refers to the wiring of motorised valves, to operate the heating and hot water independently.
Z is for…
Zoned heating system
A zoned heating system breaks your home into different areas or “zones”, each controlled separately by a thermostat. Zoning your home allows for several benefits including elimination of hot and cold spots and individual control of different rooms’ temperatures.
Zero carbon means that no carbon emissions are being produced from a product/service.