1. How can we heat our home from the air outside when it is freezing?

Even when it is freezing an air source heat pump can extract heat from the outside air. This is because the refrigerant gases used in the refrigeration cycle have a boiling point of -48°c. This enables the air source heat pump to generate usable heat for the property down to temperatures of -20°c. Obviously, the heat pump needs to work harder to extract sufficient heat when the air gets very cold.

2. Our house is older – will an air source heat pump work for us?

This will depend on how well your property is insulated and the type of heat emitters (underfloor heating or radiators). Most heat pumps cannot produce high flow temperatures and therefore your property will not heat up quickly from cold. For this reason, they run most efficiently by maintaining the property at a constant temperature with underfloor heating or fan-convectors designed for low flow temperature systems. Traditional radiators can be used but may need to be oversized.

The latest generation of heat pumps is capable of delivering much higher temperatures, similar to that of fossil fuel boilers, although they will be slightly less efficient while doing so.

The design of the heating system is crucial, whether you are using underfloor heating or radiators, so that the system is capable of giving out sufficient heat for each room.

For some older properties where an air source heat pump alone may not cope at the coldest times of the year can be docked with a fossil fuel boiler to provide supplemental heat. Such systems allow the homeowner to enjoy all the efficiencies and benefits of a heat pump whilst ensuring they remain warm all year.

3. How efficient are air source heat pumps?

The efficiency of an air source heat pump is often referred to as its Coefficient of Performance (CoP) or as a Seasonal Performance Factor (SPF). The CoP is the performance of a heat pump at a stated air temperature and flow temperature, whereas the SPF reflects the performance of the air source heat pump over a year.

As air source heat pumps rely on the ambient air as the energy source, they are more efficient in warmer weather than cold, and likewise are more efficient at producing lower temperatures for heating.

A correctly sized air source heat pump for a well-insulated home will be around 300 – 400% efficient (SPF of 3 to 4), this means that for every 1kW of energy supplied to the air source heat pump, between 3 to 4kWh of energy is delivered.

As part of the system design Fervo will advise you what the SPF of your GSHP will be and will provide an estimate as to what it will cost to run.

4. Do I need a special heating system?

An air source heat pump has the greatest efficiencies when connected to an underfloor heating system or fan convectors designed for use with a heat pump. Traditional radiators can also be used provided they are correctly sized. Many radiator manufacturers now have ranges designed for use with heat pumps.

5. Will an air source heat pump provide all my heating and hot water needs?

Yes, the air source heat pump will meet all your heating needs and hot water requirements provided it has been sized correctly for the property. Heat pumps, whilst still a relatively new technology to the UK, have been a primary heat source to homes and businesses across Scandinavia for over 40 years where tempertures are well below those experienced in the UK.

Fervo, as an accredited MCS installer are required to ensure that our recommendations meet all your heating and hot water needs.

6. Can an air source heat pump be combined with other heating/energy sources?

Yes. As with many renewable energy systems, an air source heat pump can be docked with a backup fossil fuel boiler (bi-valent heating) and can form part of an integrated renewable energy system with the likes of MVHR, solar thermal and solar PV.

A bi-valent system can be very cost-effective by designing it so that as fuel costs fluctuate over time the property owner can always ensure he is using the cheapest energy source to keep warm.

7. How much space do I need indoors for an ASHP and where should this be?

Most air source heat pump systems will comprise only two indoor elements; a hot water tank and a buffer tank (which improves the efficiency of the air source heat pump by evening out peak heat demands.) The size of the tanks will depend on the size of the property and there are single tanks available that combine both the hot water tank and buffer tank.

Some air source heat pumps are a “split” system whereby the “heat pump” element is separate to the outdoor fan unit and located in the property being the size of a small wall cupboard.

Typically, the tanks will be in a plant room, utility room, garage or airing cupboard. If planning a new build property, it is always advisable to consider where you can accommodate these at an early stage of the design and Fervo would be pleased to discuss this with you.

8. What day to day management is required for an air source heat pump system?

Most heat pump systems are “weather compensated” to keep your indoor climate at a constant temperature. When the weather turns colder the air source heat pump will work harder to produce just sufficient heat to maintain your desired indoor temperatures. This is all done automatically and makes it very efficient to heat your home. All heat pumps are a “fit and forget” technology.

9. Do I need planning permission for an air source heat pump?

There are Permitted Development rights for installing air source heat pumps that are up to 0.6m³ in volume and which comply with sound criteria. There are exceptions that fall outside the Permitted Development rights which, amongst others, include properties that are in conservation areas or are listed, or where an air source heat pump is proposed to be in an inappropriate location.

Fervo will be pleased to advise you on this.

10. Where is it best to locate an air source heat pump?

There are several considerations in deciding where to locate the outdoor unit.

  • As close as possible to the plant room to avoid unnecessary heat loss.
  • Although many air source heat pumps are extremely quiet, if possible it is advisable to position away from bedrooms where any noise could be an issue.
  • Areas that do not allow air to circulate freely around the air source heat pump or “frost-hollows” should be avoided to prevent a vicious circle of supply air from getting colder reducing the efficiencies.
  • Avoid the potential for dropping leaves or debris that could disrupt airflow into or out of the unit.
  • As the ASHP blows out cold air, locating the unit adjacent to footpaths, doorways and plants that may be sensitive to frost should be avoided.
  • A working ASHP can produce up to 25 litres of condensate a day which needs to be taken to a soak-away or drain.