An air source heat pump (ASHP) is an electric pump that transfers thermal energy from one place to another. The term “pump” can be confusing. In this instance it means that electricity is used to push heat energy from place to place. An ASHP does not directly generate heat energy.
When looking at central heating, an ASHP transfers heat energy from the air outside into the house. We will explain the actual process and how the compressor is involved in a separate post.
Due to their reliance on ambient outdoor temperatures ASHPs are commonly used in milder climates, where temperatures don’t drop below -5C. Having said that, ASHPs can still extract heat from temperatures that drop to -20C, but become very inefficient at such temperatures.
The most important point to note about ASHPs is that they don’t produce heat for central heating system to the same degree as oil or gas boilers. A typical flow rate for ASHPs is 45C, so these systems are typically left on 24/7 during winter months to keep indoor temperatures stable.
In the UK, it’s common practice to retrofit well insulated houses that have been on oil and gas boilers with an ASHP without the need to replace existing radiators. A new water heater will, however, be fitted.