Heat Pump Dictionary

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Heat Pump Glossary

We know that heat pump terminology can often be confusing. It's important to fully understand what you are reading so you can make an informed decision about the heat pump you are purchasing.

We've put together a glossary of frequently used words and phrases in the heat pump world and their definitions, so you can feel confident in the decision you make.

Air Source Heat Pump

A heat pump that sources its energy from the surrounding air. Air source heat pumps are a knee-waist high unit that sites outside the property and can be up to 400% more efficient than boilers.

Boiler Upgrade Scheme (BUS)

A government grant that offers up to £7,500 towards the cost of an air or ground source heat pump if installed through an MCS installer.


Forms part of a ground source system. It acts as the energy source for the system and comes in forms such as horizontal surface collector, borehole rock collector, closed loop lake collector, open loop / ground water collector, photovoltaic-thermal panels.


A component inside the heat pump. It maintains the flow of refrigerant through the unit and compresses liquid refrigerant into a hot gas. This then moves to the condenser coil for cooling or the evaporator coil for heating.

COP (Coefficient of Performance)

A number that shows the efficiency of a heat pump at a given moment in time. COP is calculated by dividing the energy outputted by the heat pump by the energy inputted into the heat pump. Energy out/energy in = COP. 

Exhaust Air Heat Pump

A type of heat pump that combines mechanical extract ventilation (MEV) or mechanical ventilation with heat recovery (MVHR) with the refrigeration cycle principles to create a system that provides heating, hot water and ventilation.

Expansion Valve

A heat pump component that controls the flow of refrigerant into a direct expansion evaporator. Decompresses the fluid refrigerant to allow it to vaporise in the evaporator.


A fixed speed heat pump uses a compressor that cannot change its output level. If the heat pump is listed as an 8kW output, for example, it will always operate at 8kW, regardless of the heating demand. For example in the summer the heating demand might be lower.


F-Series heat pumps are compatible with our entry level, wired SMO 20 controller and myUplink app. The NIBE F2040 & F2050 Air Source Heat Pumps are an exception to this as they are compatible with the SMO S40 controller and with the VVM S320 Hot Water Cylinder.

Ground Source Heat Pump

A type of heat pump that sources its energy from the ground. The latest NIBE Ground Source unit can be more than 600% efficient than a gas/oil boiler.

Heat Pump

Heat Pumps use air, ground or ever water sources to generate heating and hot water for your home, using the principles of a refrigeration cycle. As the heat pump is using natural heat from the environment, this heating solution doesn’t emit any carbon dioxide and is regarded as an environmentally friendly method for heating your home.

Hot Water Cylinder

Stores the hot water that has been heated up by the heat pump. NIBE manufacturer cylinders that also have an integrated control panel, as well as standalone cylinders.

Indoor Unit

A unit that sits inside the house. This includes a ground source or exhaust air type of heat pump. Hot water cylinders and controllers are also indoor units.


A type of technology that allows a heat pump to decrease its output level if the heating demand is lower, for example in the summer. An inverter-driven heat pump is therefore more economical than a fixed-speed heat pump.

Kilowatt (kW)

A measure of power equal to 1,000 watts. Used to measure heating power output and/or electrical power required when speaking about heat pumps.

Kilowatt Hour (kWh)

A unit to measure energy used over a period of time. Measures the amount of electricity used in an hour, equal to one kilowatt of power sustained.

MCS Certified

MCS (Microgeneration Certificate Scheme) is a body that creates and maintains standards for the installation of low-carbon products, including heat pumps. MCS certified installers are able to access the Boiler Upgrade Scheme grant.

Mechanical Extract Ventilation (MEV)

Ventilation system that extracts stale air from within a property. This causes negative pressure within the property which leads to air being drawn in through trickle vents within the property.

Mechanical Ventilation with Heat Recovery (MVHR)

Ventilation system that extracts stale air from within a property while simultaneously recovering the heat that would be lost from the extracted air. This improves the efficiency of the ventilation system as the amount of heat lost is reduced. MVHR systems can also replace the stale air directly through its ventilation system.


An app for your mobile phone or tablet that lets you connect to your heat pump and easily control your heating, hot water, and ventilation system. myUplink can connect to NIBE Smart home accessories, as well as support weather control and solar panel integration.

NIBE Energy Systems Ltd

The company name for the UK division of NIBE Energy Systems. NIBE Energy Systems was founded in 2006 and sells heat pumps, solar-thermal panels, cylinders and ventilation products.

NIBE Industrier AB

The global group of which NIBE Energy Systems Ltd is a part of. NIBE AB is a global group with over 21,000 employees and a revenue of £3.5bn in 2023. NIBE is the largest heat pump manufacturer in Europe.


A partnership scheme for heating installers to make the transition to heat pump installers. NIBE Pro supports installers through the entire training process, enabling them to install NIBE products proficiently and safely to a high standard.

Outdoor Unit

For air source heat pumps, the outdoor unit is a component of the whole system that sits outside the property. Exhaust air heat pumps do not have an outdoor component while ground source units have outdoor groundworks.


Refers to the outputted energy of a heat pump that is used to heat a property. The output of a heat pump is measured in Kilowatts (kW).

Photovoltaic-Thermal (PV-T)

PV-T panels are equipped with PV cells at the front that convert sunlight into electricity. The rear consists of a thermal heat exchanger that extracts energy from the ambient air that is heated under the panels. Even on cloudy days and at night – without direct heating of sunlight and even at temperatures below freezing, the heat exchanger provides sufficient heat to supply a heat pump. 


The chemical fluid that’s used in heat pumps to change energy from a gas to a liquid state, and back again. Refrigerants can be more or less efficient and have varying impacts on the environment.

Refrigeration Cycle

The refrigeration cycle is the core principle of how a heat pump works. Every heat pump operates using the refrigeration cycle. The heat pump uses low grade energy to change the state of a refrigeration fluid from a liquid to a gas. During this change of state high grade heat energy is produced.

SCOP (Seasonal Coefficient of Performance)

A number that shows the efficiency of a heat pump over a period of time. SCOP gives a better reading of heat pump efficiency as it takes into account factors such as weather, temperature and seasonal changes. SCOP is calculated using a European standard called EN 14825.

Smart Accessories

Can be paired with an S-Series heat pump to control and monitor your heating and ventilation system simply and easily in combination with the myUplink. 


NIBE’s flagship heat pump range, our S-Series heat pumps can be combined with our premium wireless SMO S40 controller, VVM S320 hot water cylinder, myUplink app, and our Smart Home Accessories.


Refers to the extraction of stale air within a property and the process of replacing it with fresh air using mechanical extract ventilation (MEV) or mechanical ventilation with heat recovery (MVHR). 

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