Air source heat pumps are a really popular way to heat your property these days, but most of the attention, at least for homes, is focussed on air to water heat pumps for wet central heating systems. These types of heat pumps are fairly efficient, and can be swapped in to replace other conventional wet systems really easily, without changing your radiators.
There are however, air to air heat pumps, which take cool air from the outside and use a condenser to take the temperature up to a level that can be used to heat the house. They work just like air conditioning units in reverse, and they can be used to both heat and cool the property. The only real difference is that air to water pumps have a heat exchanger which converts the heat in the air to warm water, of course allowing the warm water to be used in the central heating system.
RHI for heat pumps
Unfortunately the RHI is only currently available for grand/air to water heat pumps. It can be speculated that this is because many air to air pumps are purely used for air conditioning, and it would be too difficult to differentiate for the purposes of government funding.
For air to water, the funding from the RHI is fairly generous, with several thousand pounds usually available for the average property, spread out over a 7 year period of payments. A really nice incentive!
Hot water an advantage
One advantage of air to water heat pumps is that you can heat your hot water as well as your central heating. With an air to air heat pump, you can’t do this and you have to rely on an immersion heater for your water needs. Immersion heaters are a pretty inefficient way to heat your water and your hot water bill is going to be at least double that of a heat pump heated system.
Does this mean air to water is better?
Whilst most domestic properties in the UK go for air to water, the opposite is true in the US. Why is this? This is probably because of the fact that America has more extremes of temperature, and many homes require cooling in the summer as well as heating in the winter. Air to air heat pumps can cool as well as heat, so they are well suited to dealing with the demands of a region with big ranges in temperature.
Unfortunately, if you are looking to retrofit an air to air heat pump, you will need to install ducting, and this can be really tricky and tends not to look too nice unless it is installed when the house is built. Air to water pumps on the other hand need a radiator or underfloor system, which can be equally expensive to install.
So if you want to have your heating and cooling all from the same system, then an air to air heat pump might be a useful option. The other thing is that it will depend on the current system. If you are retrofitting a property, it is obviously going to be cheaper to install an air to water in a home where radiators are already present, whereas a house that already has ducting, but no radiators is going to much less expensive to install an air to air. If the house is bare with no heating system, it is going to be a case of weighing up the additional RHI money for going with an air to water, over the warm air option.
But given the RHI funding, hot water heating and ease of integration, it really makes sense to go for the air to water option in the majority of cases.