A-Z of retrofit

Do you want to retrofit your home but find the words and messaging around the process a bit overwhelming? Allow our retrofit glossary to do the hard work for you.

A man and woman drink tea and look at their latest energy bill.


Air source heat pump – A type of central heating. It takes heat from the air outside, boosts it, and uses this to warm our home.


Battery storageA way of storing electricity for later use. Often connected to solar panels.

Biomass boilerHeating system that burns organic matter, such as wood.

Boiler Upgrade Scheme (BUS) – UK Government scheme for England and Wales. Offers grants to replace boilers with heat pumps or biomass boilers.


Carbon emissions – The carbon dioxide (CO2) released into the the atmosphere from burning fossil fuels.

Carbon footprint – The amount of carbon emissions that someone or something (e.g. a country, a company, or a person) creates through their activities.

Cavity wallsType of external wall. There are two layers of brick with a gap (cavity) between them.

Cavity wall insulationInsulation inserted into the cavity of cavity walls to slow down heat loss.

Cold spots – Area of a surface (often a wall) that’s colder than the rest of the surface. Often the result of poor insulation.


Double glazing – Windows that have two panes of glass with a gap between them. This reduces heat loss.

DraughtsAir coming into your home through a gap in its construction.

Draught proofingBlocking gaps in your home’s construction to keep warm air in and cold air out.


EcoCosiOur home retrofit service. Here to support you on every step of your journey to a low-carbon home.

Electric vehicle charging point – A place to charge an electric vehicle. These can be found in public places or installed at home. Find your nearest public charge point here.

Energy efficiency – How much energy it takes to get the result we want, e.g. heating our home.

Energy efficient – Something that provides us with the result we want – such as heating our home – by using relatively little energy.

Energy efficiency rating – A rating for appliances (such as TVs, washing machine) that tells you how energy efficient it is. The scale runs from A+++ (most efficient) to G (least efficient).

Energy efficient lighting Lights that use relatively little electricity, such as LEDs.

Energy Efficient Scotland: Area Based Schemes (EES: ABS) A Scottish Government funded scheme to help householders install energy efficiency measures.

Energy Performance Certificate (EPC) – A document that shows the energy efficiency of a building, including predicted running costs.

Energy Performance Certificate (EPC) rating Tells homeowners how energy efficient their property is on a rating of A (very efficient, lower running costs) to G (very inefficient, high running costs).

Energy Saving Trust – Organisation providing independent advice and support on energy efficiency.

Energy tariff – The plan that sets out how much you pay your supplier per unit of gas and/or electricity, plus any standing charges.

External wall insulationExternal wall insulation is installed on the outside walls of a building. It helps make the building more energy efficient by reducing heat loss.


Fabric first Type of retrofit which focusses on improving your home’s ability to retain heat. Anything that separates the outdoors from the indoors – floors, walls, windows etc. – is upgraded.

Feed-in-tariff (FIT) – Discontinued UK Government initiative. Householders received payment for generating low-carbon energy.

Flat roof insulation – A layer of rigid insulation board, usually installed from above rather than below a flat roof.

Floor insulation Layer of insulation installed under the floor to retain heat in a building. This is especially useful in older properties with old floorboards.

Fossil fuels – Fossil fuels are non-renewable energy sources such as coal, natural gas and oil. These have long helped to provide energy for human consumption. However, the carbon they produce is doing serious damage to the planet.


Grants – Financial help to improve your home’s energy efficiency. Unlike loans, grants don’t have to be repaid.

Greenhouse gas – Gasses released from burning fossil fuels. These stay in the Earth’s atmosphere and trap heat, leading to global warming.

Great British Insulation SchemeUK Government scheme providing free or discounted home insulation.

Green Deal – Discontinued UK Government scheme. It helped fund home energy efficiency upgrades.

Ground source heat pump (GSHP)A type of central heating. It takes heat from the ground outside, boosts it, and uses this to warm our home.


Heat loss – When heat escapes from inside a building to the outdoors, usually due to a lack of insulation.

Heat pump – Low-carbon central heating. Depending on the type of heat pump, it uses energy from either the air, the ground, or water to heat our homes.

Hot water cylinder – A water tank with a heating element inside. It heats and stores water for use around the home.

Home assessment – A survey of your home to measure its energy efficiency.

Home energy plan – The list of things you can do to make your home more energy efficient. It’s based on the home assessment.

Home Energy Scotland (HES)Impartial energy-saving advice service. Changeworks delivers Home Energy Scotland in the Southeast and Highlands and Islands on behalf of the Scottish Government and Energy Saving Trust.

Home energy storage – Systems (like solar batteries) that let you store renewable energy so you can use it later.


InsulationA layer of material that slows down heat loss. It’s the first step in keeping your home warmer.

Internal wall insulation Insulation installed on the indoor side of an external wall. It helps make the building more energy efficient and reduce heat loss.


Kilowatt – A unit of power, measuring how much energy an appliance needs in order to run. 1 Kilowatt = 1,000 watts.

Kilowatt-hour (kWh) – A unit for measuring how much energy we use in the home. Both gas and electricity usage are measured in kWh.

K-value – Measures how easily heat passes through a material. Insulation usually has a K-value. Lower K values mean better insulation.


LED lighting Modern, energy efficient type of lighting. They use 90% less energy than old incandescent bulbs, and 50% less than older energy saving bulbs.

Loft insulation –  Insulation installed in a loft, which helps slow heat loss through the top of your home.

Low carbon – Something that involves burning relatively little carbon (fossil fuels) to produce energy, e.g. a low carbon heating system.

Low-emissivity (low-e) glazing – A type of glazing that slows heat loss through windows.


Microgeneration Certificate Scheme (MCS) – Organisation that creates and maintains standards for the energy efficiency industry.

MCS certified – Products, installers, and installations that meet MCS standards.

Mechanical Heat Ventilation Recovery (MHVR) – Energy efficient ventilation system. It extracts heat from outgoing air and uses this to warm incoming air.


Net zero – Balance between greenhouse gas emissions produced and removed from the atmosphere.



Passive house – A highly energy-efficient home relying on sunlight and ventilation for temperature control.


Quality assurance – A check to ensure that work is carried out to the correct standards.


Radiant heating – Heat that’s transferred directly from a surface. Underfloor heating is a common example.

Renewable energy – Energy from natural sources which can be replaced faster than they’re consumed. Examples include wind power and solar energy.

Renewable Heat Incentive – UK Government scheme (closed to new applicants) where householders receive payment for using renewable heating systems.

RetrofitInstalling new energy efficient measures to buildings to make them warmer and more affordable to heat, e.g. replacing a gas boiler with an air source heat pump.

Retrofit assessorA professional who surveys your home to calculate its energy efficiency.

R-value – Measurement of thermal resistance. Higher values mean higher heat resistance.


Standard Assessment Procedure (SAP) – Methodology used by the UK Government to estimate the energy performance of homes.

Smart meterA meter that records energy use in real-time. Both gas and electric meters can be smart. They send readings to your supplier automatically, resulting in more accurate bills.

Smart thermostat – Tech that lets you control your home heating remotely, e.g. from an app on your mobile.

Solar panelsSolar panels catch the sun’s energy and turn it into electricity that we can use in our homes. They are typically installed on a roof.

Solid floor insulation – A solid floor is made up of layers. To keep your home warmer, insulation boards can be added either above or below the concrete or screed layer.

Solid wall insulationSolid wall insulation can be installed on the inside (internal wall insulation) or outside (external wall insulation) of a building. The insulating layer will improve the building’s energy efficiency by reducing heat loss.

Standard gas boiler – System which burns gas to provide heat and hot water to your home. The hot water is stored in a hot water cylinder.

Suspended floor insulation – A suspended timber floor is made up of floorboards sitting on top of a frame. Insulation is usually added below, but can also be added from above.


Thermal bridging – A gap in insulation which allows heat to escape.

Thermal imaging – A technology, usually a camera, that lets you see where heat is escaping from your home.

Thermostatic radiator valve (TRV) – Device that allows you to set and maintain the temperature of a radiator.

Triple glazing Windows that have three layers of glass. This will ensure better insulation meaning a warmer home. Triple glazing will also ensure better soundproofing.

TrustMark – UK Government-endorsed quality scheme for work carried out in or around your home.


Underfloor heating – Network of pipes or cables installed under your floor. These provide heating underfoot.

U-value – Measure of overall heat loss through a particular section of your home, e.g. the roof. A lower u-values mean less heat loss.


Ventilation Ventilation ensures air can move in and out of a building, replacing stale air with fresh air from outside. Ventilation is important to avoid damp, mould and condensation.


Watt – A unit of power, measuring how much energy an appliance needs in order to run. For example, a 60 watt lightbulb needs 60 watts of power to run.

Workmanship guarantee – Safeguard that covers the quality of work, including fixing defects.


Zero Direct Emissions Heating (ZDEH) – Type of heating that doesn’t produce any carbon emissions at the point of use. A ZDEH system might still produce indirect carbon emissions, for example, a heat pump which runs on non-renewable electricity.

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