Talk to me about air source heat pumps

[RidingMyBike]

We've just had an offer accepted on a house that needs a lot of work, including replacing an old boiler. It's been a longterm aim to have solar panels but we're also looking at an air source heat pump and had favourable comments from friends who have installed one - although they weren't on mains gas so have saved a lot not having to buy heating oil.

Any thoughts? Pros, cons? Things to watch out for?

I guess it depends to an extent what capacity your panels have and how much hot water you use, but we can almost always heat our tank with solar alone. It's really only days where it's overcast all day that we need to boost it with the boiler.

Tbh, most of our hot water is used for washing dishes, and a kettle is fine for that. (We were without hot water or heating for nearly three weeks when the oil fired boiler broke down the other year, so have experience.) Our showers are electric. You really appreciate the luxury of hot water when you've missed it for a while!

There's no need to turn it off, it's all controlled by a thermostat in each room so if the temperature is above that in spring/summer/autumn it won't trigger the heating. This also means that if you have a colder north-facing room or similar you can set it for different temps/times to warmer parts of the house. Same for if there are rooms you use less during the day eg we have bedrooms set to cooler than downstairs

Ours does the hot water too but is set to do that once a day when electricity is cheap. The hot water tank is extremely well insulated so we appear to only need it to heat water every second or third day.

All this information is brilliant, thank you all so much! My living room is probably the coldest room in the house, so I could set the thermostat higher than in e.g. my bedroom (which I prefer cooler) and keep the upstairs temperature down when not in use? If I wanted to heat an upstairs room, does it take long for that to happen? My grandson stays most weekends and is at an age where he pretty much lives up there, so would I reset his thermostat on Friday afternoon a few hours before he arrives, or could he reset it when he gets here, and be warmer quite quickly?

Objective advice:

Try again

Also

Gggrrrrrt sorry!

This!
https://www.bbc.co.uk/sounds/play/m0016pvn?partner=uk.co.bbc&origin=share-mobile

I have one on 1930s semi. Replaced radiators, but don't have underfloor heating. Have loft and cavity wall insulation.
People always say they don't heat house to very warm temperatures, but in winter, but mine heats to 19 degrees nice and quick, which I think is plenty. You need outside space for the unit obviously. They aren't pretty and you can't cover them up, but I'm not fussed about that!

They don't create 'free energy' but the energy they use to run takes less energy than it harvests from the air...
So they can achieve 300% efficiency... That is for every 1 unit of energy you buy to run it, it can extract 3 units from the air... and supply it to your home... So it isn't 'creating' energy hence it can achieve those efficiencies.

It is this efficiency ratio that allows it to be cheaper than gas boiler because of course gas is cheaper than electricity, so you need to get more bang for your buck out of it for it to be economical.

It can only be that efficient if it is able to run slowly hence you need to put it in a house able to retain heat well. If your house isn't insulated will enough it will be forced to run at a higher level and will lose efficiency.

A friend has had one installed in the past year, and although you can't hear it much from inside the house, outside it is a noisy hum, so really irritating for the neighbours. In order to get the right level of insulation, the interior of all the external walls had layers of insulation added, which made all the rooms smaller, too. It wasn't a big house to start with!

Also - what about if you like to have windows open? People say how important it is to have good insulation, but we're a very 'fresh air, windows open' kind of house, even in the winter, so I'm not sure it would be much good for us - it would be constantly working to heat everything up. Plus, our house is 100 years old

Happy to be advised otherwise!

We've had our ASHP for about 18 months now. In Scotland. Love it. Best heated house I've lived in and cheaper than the gas boiler we had before.
1970s house with double glazing and now with cavity wall insulation in most rooms (except living room which wasn't suitable) and loft and underfloor insulation.

It's free in the respect that you get more energy out than you put in to run it, with the caveat that you have to buy the equipment to do that in the first place.

Getting 3 units of energy out for every 1 you put in sounds like a good deal.

Until you see the price of the equipment, which may be significantly more than what the energy gain would cost over the lifetime of the equipment.

It's arguable whether it is cheaper than gas. I think electricity is 3.5x more expensive (but remember gas boilers are only around 90% efficient). The best heat pumps I think can achieve an energy multiplier of 4. But here's the rub, they only achieve that when the weather outside is relatively warm. When it is cold it is much less. And not surprisingly, it is when the weather is cold outside you use the most energy to heat your house !

There are some improvements made to the pumps that improve the energy gain (double stage), but my guess is that even with these the pumps would struggle to beat gas when the weather is cold and they push up the equipment price a lot.

As for the Scandanavian "mystery", the reason why they are used so much over there is because a) the houses are better insulated in general and so need much less energy to heat full stop, and b) they have no alternative to mains gas other than wood - the UK is quite unusual as most countries simply don't have a mains gas network which provides cheap convenient energy.

IMO the only way heat pumps will compete economically with gas is either if the gas price increases, or the electricity price falls, or the government starts taxing users of gas a lot more in some way. My guess is the government is far more likely to put a tax on gas and boilers to reduce the competitiveness of gas, than it is to lower the price of electricity.

The TLDR of all this is that its pretty complicated to figure out whether a heat pump is a good/cheap option for any individuals circumstances, and there are a lot more factors than those above in doing that calculation. I don't think it is surprising many people choose to play safe and go for a 3K boiler replacement rather than risk a heat pump, with all the complexity and potential costs associated with that option.

So in colder months we have bedrooms set to 18 or 19 degrees overnight, dropping to 16 or 17 in the day, living rooms, office etc (ie where you just sit) at about 21 degrees during the daytime. Kitchen a bit cooler, same with landings, hallway and with slightly different timings as some of those get solar gain at different times of day. Once the system had been on for a few days it maintained at this level easily and goes up 4-5 degrees fairly quickly. We have it set to the required temp for half an hour before we need to use the room (eg bathroom half an hour before alarm goes off, office half an hour before due to start work). It was cold when we first moved in and took more than a day to get up to those figures as the house had been below 5 degrees for months!

The thermostats we have are individual per room so, on first floor, there is one per bedroom, one for the landing, one for the bathroom and one for the bathroom towel rail. It's a bit trial and error but if you had a less used bedroom you could set it for only the days you need, allowing time for it to warm up, or it might be better to maintain it at 16 degrees or whatever minimum, then increase when there's actually someone using the room. Bear in mind though you'd need to keep the door shut as otherwise that room being at a lower temp would lower the temp of the landing so that would then require more heating, if that makes sense?

Well, same as if you were heating with a gas boiler or a wood fire - having the windows open means more cold air from outside coming in so you'd use more energy to maintain the temperature? Same effect whatever the heat source!

@HirplesWithHaggis not sure if I made total sense with the thermostats - we have 13 thermostats, all of which are set individually and are 24/7 so you can set different heat periods for each room for each day of the week if you so desire.

It was a bit of a faff setting them up initially(!) as had to do each in turn, but then it's been straightforward to tweak each as we've found out how the house responds to the heating, worked out where the sun is during the day etc! Each has an over-ride/boost thing which we used a bit initially if we hadn't got it quite right but haven't needed those since.

They all have a simple button to turn on a holiday setting that just puts on frost protection if we did want to go away and maintain a minimum temp to protect pipes. So wouldn't have to go through resetting the whole thing from scratch again.

I imagine it's also possible to get it set up with an app so could be controlled remotely but that's not something we were interested in.

It will be a poorer solution for heating up the room rapidly after opening and closing the windows to let air in.

The reason is heat pumps are lower power output than boilers. So if you let all the hot air out, it will take longer to heat the room back up to temperature than it would with a typical gas boiler.

If you leave the windows open all the time, it depends. If the heat leak from the windows is greater than the amount of energy the heat pump can deliver into that room (which may be the case and may not) then the room will not heat up but will equilibrate with the outside temperature.

It's a similar situation for a gas boiler, but the difference is that because gas boilers are much higher power, they are more likely to be able to deliver the energy to accommodate heat leak from the windows.

With a heat pump, the lower energy output means they are generally designed to be on all the time, keeping the room at a constant temperature (which isn't helped by opening the windows). Gas boilers are better at heating up rooms from scratch, or coping with large heat leaks that may come from open windows or poor insulation. Which is why some people complain of cold houses with heat pumps - the pumps simply cannot deliver the energy to match the heat leak.

very noisy during those cold days. I hope council will regulate these ASHP soon.😥

Thank you so much to everyone again. I'm starting to get my head round the concept now, and can see it's something I'm going to have to learn to live with, as in figure out the most efficient way to make this work for us. If we were paying for it ourselves I'd have done all the background research and be able to chat about SCOP, and solar batteries and so on but as it is, although I alerted my landlords to the opportunity (and knew they'd be interested) I have no choice in what I actually get. The installation company seem to be discussing the technical details with the LL (fair enough, it's their house) while I just get the pleasure of random men in my home, so I think I feel a little overwhelmed and disempowered. You're all helping me feel much better about it all. Am now both excited at the thought of not shivering in blankets all winter, and a bit wary of the disruption involved, while dreading the amount of redecorating (every room in the house!), and thinking it'll all be worth it in the end. Gah.

They told me it'll all take about a fortnight, I do hope that's true.

Our whole street has them - some of them are on the external walls beside paths. I can't hear them when I'm walking past, I can't hear my neighbours and I only hear mine if I walk up to it. It's about as loud as a decent modern fridge.

I'm sure there are some set up badly but they certainly aren't always problematically noisy

Ours is about as loud as a fridge. So you can barely hear anything!

Useful thread, thanks, because we are getting a survey done and hoping to benefit from the government grant.

@Calling
great

coming back here to say that this winter is the first proper test with ours, installed in April. Anyway last few weeks have been nice and warm at home. All the time.
And no we can’t hear ours either. And thus far it’s costing less in bills than we thought. Happy days.

would not have one ever again - we inherited one when we moved in to this house - noisy - fans cutting in and out - not very good system you end up using various different heating methods and supplementing the heating it takes up room - looks an eyesore and you cannot beat
gas - switch on and off or timed. as for servicing forget it - hard to find engineer and expensive and if breaks down can be days before they can repair or get parts.

Unfortunately it sounds like yours was poorly installed, obviously beyond your control

properly installed by someone that actually understands them (granted there are not that many) they are great

I was recommended an installer by a mnetter and he was fantastic. Made sure we had the right radiators (if you don’t, you will be cold). He’s been back several times since the install to tweak the hardware and make sure we’re happy. Any issues with it we know he’ll come and sort it out. But I think we’re lucky in that regard