Heat Pump Glossary

Plain-English definitions of the technical terms you will encounter when comparing heat pump brands for your Scottish home.

ASHP

Air Source Heat Pump — extracts heat from outdoor air, even in sub-zero temperatures, to heat your home and hot water.

COP

Coefficient of Performance — the ratio of heat output to electricity input at a single measured temperature. A COP of 4 means 4kW of heat from 1kW of electricity.

SCOP

Seasonal Coefficient of Performance — the average COP across a full heating season. More useful than COP for comparing brands in Scotland's climate.

Flow temperature

The temperature of water sent to your radiators or underfloor heating. Lower flow temperatures (35-45°C) give higher efficiency.

EPC

Energy Performance Certificate — rates your home's energy efficiency from A (best) to G (worst). Required for government grant applications.

MCS

Microgeneration Certification Scheme — the UK quality standard for renewable energy installations. MCS certification is required for government grant eligibility.

R290

Propane refrigerant — a natural refrigerant with very low global warming potential (GWP of 3). Used in Vaillant aroTHERM plus.

R32

A synthetic refrigerant with moderate GWP (675). Used in Daikin Altherma, Mitsubishi Ecodan, and Samsung EHS.

R410A

An older synthetic refrigerant with high GWP (2088). Used in NIBE F2120. Being phased out under F-gas regulations.

Buffer tank

A small water tank that smooths heat pump operation, reducing start/stop cycles and improving efficiency. Not always required.

Defrost cycle

An automatic process where the heat pump briefly reverses to melt ice from the outdoor unit in cold weather. All brands handle this; it typically takes 2-5 minutes.

Weather compensation

A control feature that adjusts flow temperature based on outdoor temperature, maximising efficiency. Standard on all modern brands.

Hybrid system

A heat pump paired with an existing boiler. The boiler covers peak demand on the coldest days. Useful for properties where a full heat pump would be oversized.

dB(A)

Decibel measurement weighted for human hearing. Heat pump outdoor units typically range from 38-56 dB(A) at 1 metre — comparable to a fridge or quiet conversation.

Legionella cycle

A weekly automatic pasteurisation of the hot water cylinder to 60°C, killing harmful bacteria. All brands support this.

TRV

Thermostatic Radiator Valve — controls individual radiators. Important for zoning with heat pumps.