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!
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.
I have recently installed three air-to-air heat pumps to replace old electric storage heaters.
The outdoor units (Daikin Ururu Sarara R32 – ftxz25n) are very quiet under most circumstances, and operating the bedroom unit in “night mode” overnight makes it quiet enough to be almost unnoticeable – certainly quiet enough not to disturb our sleep. The Daikin R32 units have an SCOP of about 5.9, and test results available online from “Eurovent” in France showed a CoP of about 3 even at a source temperature of -15C. So far, with just two units operating I currently seem to be using about 11kWh per day for heating when external temperatures are in low single figures. My wife is a little unconvinced – though the cats are getting to love the warm draft from the bedroom unit!
Total installation cost was about £8,000 including electrical works, drains for condensate, etc. That compares to about £16,000 for a system with low temperature fan “radiators” usable with air-to-water.
As well as the heat pumps I installed an oversized Solar PV array last year (9 kW inverter, though it rarely produces above 8kW even in the summer). On the plus side, we’ll get “free” cooling in the summer (the PV array will produce vastly more power than the heat pumps require on the relatively few days when cooling might be required).
The plan for the hot water is to replace the current immerser based water tank with a new mains-pressure heat pump hot water cylinder (probably an Ariston or Giona unit), which will also allow me to get rid of the cold tank in the attic and further improve my attic insulation!
We don’t get an RHI payment, but on paper at least the efficiency should compare very favourably with air-to-water heat pumps and the up-front capital cost was a lot lower. Comfort is probably not quite as good (the indoor unit produces a warm “breeze” which some may find distracting), but personally I’m not keen on radiators anyway and I’m trying to be as green as possible, so better efficiency is a big point. Note that the Daikin units have just about the highest SCOP available – but there are other A2A heat pumps with similar efficiency but which are noticeably cheaper (e.g. from Mitsubishi).
Generally the high efficiency A2A units are relatively “small” – typically rated at about 2.5-3kW for heating, so you will probably need more than one unless you have a very well insulated modern house. You will also likely have to leave doors open to allow heat to circulate to rooms which don’t have their own units.
Hi Justin, Without wishing to appear at all ‘-ist’, would I be right is saying you may be located north of ‘the border’… (going from your name)?
I ask as I have installed a simple air-to-air HP in my home on Colonsay (southern Hebrides) and at £600 (but installed on a DIY basis – very easy!) it is turning out to be a very nice investment. I installed the internal unit in my study, where – if I’n in during the day – I spend most of my time. Leaving the door to the living room open takes the chill of that space too but I have a woodburner (with free logs) to keep that warm in the evenings. When I moved in, there was one of those utterly fraudulently advertised (IMO) electric panel heaters (a Rointe but the rest are just as bad eg Fischer) which, to maintain the study at a similar 20C temp as the AtA HP, cost easily 3 times as much to run.
My only grumble is that, being marketed as ‘air conditioning’ the instructions advocate installing the internal unit high up on the wall – obviously good for cooling, but not so much for heating when really you want the indoor unit as close to the floor as possible to provide warmth at ankle level (which then rises). And this does seem to be a massive problem for the industry at the moment, given that it is entirely geared up for air conditioning and the generally ill-educated (to heat pump technology) general public can’t make the leap.
So it seems to me that we need a huge education program to highlight the advantages of simple, inexpensive systems like mine particularly for use by those who are currently relying entirely on electric space heating where the replacement of electric panel heaters in primary occupation areas by AtAHPs in a home could reap huge financial benefits, maintaining panel heaters for flexibility and topping up where required. It does seem a shame that AtA HPs are outside of the scope of the government scheme, but then, as we all know, they’re even more ignorant than the rest of us, aren’t they?
I inherited an air to air heat pump system (Daikin Inverter) when I bought this bungalow five years ago. The system had been installed by the previous owners some seven years prior to that at a cost of around £25,000 so I was told. Fifteen months ago one of the three units rokr down and after several attempts to repair it, I eventually paid out nearly £4000 for a new compressor, main board and when it still didn’t work a PCB module. This January the same unit failed again. At first I was told it was the fans, then the Active module board and when it still didn’t work I was told that the compressor and main board needed replacing again and they were over the one year warranty period. I have now been without heating in my main living area for over a month and don’t know what to do for the best. I don’t know what to do for the best but am not prepared to throw more money at this system. I have travertine flooring throughout the main areas of the house and vents in the ceilings so underfloor heating or radiators would not work. Is there a similar A2A form of heating that would give me a more reliable form of heating/cooling that would come with more than a years warranty. I have little faith in the company who originally installed the system but have had no luck with Daikin and desperately need advice.
… Which rather neatly illustrates the other problem with heat pump technology currently, that being that there are extremely few individuals adequately trained and experienced to rectify this sort of issue. Plenty of cowboys around to spend the governments money installing them, of course!
Quite why everything is so horrendously expensive (other than the fact that it’s all relatively new from a heating perspective) I do not understand, given that prices for simple air-conditioning units are so low by comparison but I guess everyone’s jumping on the bandwagon, as usual with new technology, despite the fact that it is, of course, exactly the same as ‘air-conditioning’ technology.
I hope you can find a solution and I would certainly advise persevering but it does seem like you must endeavour to track down an expert… But good luck with that! Could it be that the one unit that failed is not the only issue with the system?
I have no informed opinion other than have a good fire raging and plug in economy seven electric storage rads. You’ll never need servicing clowns with their extraordinary crippling bills only to watch them driving away in their Mercedes Benz’s. What’s more you won’t suffer the anguish of system failure when you least want it. It seems the more sophisticated we try and get the more the industry is unable to cope with servicing and repairs. All their energy is reserved for selling selling selling. Heat pumps are the biggest rip off. The colder the weather the less they can suck atmospheric heat, so everyone’s going to be walking around plugged into an electric blanket. Just my humble take on this racket.
“Immersion heaters are a pretty inefficient way to heat your water” Sorry, but this is abject nonsense. They practically 100% ‘efficient’. Perhaps what you meant to say is that they are ‘pretty *uneconomical* way to heat your water”. Of course a typical heat pump is 3 times or more as efficient… but for some reason you don’t draw the comparison!