Air source heat pump FAQ

An air source heat pump (ASHP) is a heating system that extracts heat from outside air and moves it into your home, similar to how a fridge extracts heat from inside and releases it behind the unit, but in reverse. Because it moves heat rather than generating it by burning fuel, it can produce 3–4 units of heat for every 1 unit of electricity it uses, making it significantly more efficient than a gas boiler.

Yes. Modern inverter heat pumps work efficiently down to -20 °C ambient temperature. All Thermotec units are cold-climate rated and maintain meaningful output even in the hardest UK winters. Efficiency (COP) does reduce as it gets colder, but the system keeps heating your home, it simply uses slightly more electricity on the coldest days.

Running costs depend on your home's heat loss, insulation standard, and the current electricity price. A typical 3-bed semi heated by an 8 kW heat pump running at a COP of 3.5 would use roughly 4,000–5,000 kWh of electricity per year for space heating. At current UK rates (~28p/kWh), that is approximately £1,100–£1,400/year. This compares to £1,200–£1,800/year for gas, and the gap widens as gas prices rise. Use the government's Heat Pump Calculator for a precise estimate based on your home.

For many homes, yes, particularly well-insulated ones. Because heat pumps use electricity and electricity is currently more expensive per kWh than gas, the advantage depends on your home's efficiency. A well-insulated home with a heat pump running at COP 3.5+ will typically pay less to heat than the same home with a gas boiler. The government's Smart Export Guarantee and time-of-use electricity tariffs (like Octopus Cosy) can reduce running costs further.

The Boiler Upgrade Scheme (BUS) is a UK government grant of £7,500 towards the installation of a qualifying air source heat pump. It is paid directly to your MCS-certified installer, reducing the upfront cost. To qualify, your property must have a valid EPC (Energy Performance Certificate) with no outstanding recommendations for loft or cavity wall insulation. The scheme is administered by Ofgem. Thermotec units are MCS eligible.

You likely qualify if: (1) your property is in England, Scotland or Wales; (2) you have a valid EPC with no outstanding loft or cavity wall insulation recommendations; and (3) you use a registered MCS installer. The grant applies to owner-occupied and landlord-owned properties. Social housing, new-build properties receiving government support, and properties that received an earlier RHI payment are excluded.

Sizing depends on your home's heat loss, which is affected by floor area, insulation, window quality, and ceiling height. As a rough guide: a well-insulated 1–2 bed flat typically needs 5 kW; a 2–3 bed semi needs 8 kW; a 3–4 bed detached needs 10–12 kW; a 4–5 bed or older poorly-insulated home needs 14–16 kW. An MCS installer will perform a full heat loss calculation (BS EN 12831) before recommending a size. Do not use a rule-of-thumb to make the final decision.

Yes, but the Boiler Upgrade Scheme grant requires your EPC to show no outstanding loft or cavity wall insulation recommendations. If your walls are solid (pre-1920s brick), cavity insulation is not applicable, your EPC will show this and you will still qualify. If your property has unfilled cavities, you can have them insulated first and then apply for the grant.

A typical heat pump installation takes 1–3 days. The outdoor unit is placed on a wall bracket or ground slab outside. Pipework runs into your plant room or utility area where the heat pump connects to your existing pipework. If you are keeping wet radiators, your installer will check they are adequate for lower flow temperatures, some may need upgrading. Underfloor heating is ideal and usually requires no changes.

Not necessarily. Heat pumps work at lower flow temperatures than gas boilers (typically 35–50 °C vs 70–80 °C), so existing radiators sometimes need to be upsized to deliver the same heat output. A good installer will calculate this room by room. Many UK homes have slightly oversized radiators already, and in well-insulated properties the existing radiators work fine without changes.

Underfloor heating is the ideal heat emitter for a heat pump because it operates at 30–40 °C flow temperatures, exactly where a heat pump is most efficient. If you have underfloor heating already, a heat pump should work very well with it.

Yes. Air source heat pumps can heat domestic hot water using a hot water cylinder (typically 200–300 litres). The cylinder stores hot water at 45–55 °C. A legionella prevention cycle runs periodically to heat the water to 60 °C. If you have a combi boiler and no cylinder, you will need to fit one as part of the installation.

Modern inverter heat pumps are much quieter than older fixed-speed units. Thermotec units produce 40–49 dB(A) at 1 metre, depending on model, roughly equivalent to a quiet conversation or a refrigerator hum. Planning rules in England require the unit to produce no more than 42 dB(A) at 1 metre from a neighbouring window or door, measured under Permitted Development rights.

In most cases, no. In England, Wales, and Scotland, air source heat pumps fall under Permitted Development rights as long as certain conditions are met: the unit must be on a wall or roof facing away from a highway, or on the ground; it must be at least 1 metre from the property boundary; and it must not be in a conservation area, AONB, or listed building. Your installer will confirm whether PD applies to your property.

A well-maintained heat pump should last 15–20 years. The main consumable components are the compressor, refrigerant, and fan motor. Annual servicing by a qualified engineer is recommended. Thermotec units carry a 5-year warranty as standard, with extended cover available.

Heat pumps require minimal maintenance compared to gas boilers. Recommended tasks: keep the outdoor unit clear of leaves and debris; check the filters periodically; arrange an annual service with a qualified heat pump engineer. There is no annual gas safety certificate requirement. The refrigerant circuit is sealed and should not need topping up.