Non-motoring > Air source heat pumps Miscellaneous
Thread Author: smokie Replies: 29

 Air source heat pumps - smokie
Octopus have given me a quote which seems v reasonable for an ASHP. They are yet to do a survey so that could change.

However I can't seem to get to the bottom of how much they cost to run, maybe in KwH. Some of the online resources indicate a potentially massive amount at the top end.

Does anyone have any real -life ball-park experience they can share please? I realise that each house can be very different... but I imagine you must have at least some idea of roughly what it costs to keep the house warm.

 Air source heat pumps - Terry
A very crude comparison.

Current cost per kwh for electric is 27p for electricity and 7p for gas. These can and no doubt will change over time.

The SCOP - seasonal coefficient of performance - for a heat pump typically ranges from 3.0-4.0 depending on system and ambient temperatures.

So for 27p electricity you get the heating equivalent of 21-28p gas - not a clear answer!!!

The real questions may be:

- will changing the heating system will allow greater control and give you efficiency savings,
- what level of domestic disruption is required for installation,
- do you eliminate radiators and swap for indoor fan units which cool as well as heat
- if gas boilers are banned as part of net zero - the price of gas and infrastructure may rise
 Air source heat pumps - smokie
Hmmm OK it's not an easy one then.

At the moment my gas is more like 5p and my elec around 20p (Octopus tracker tariffs - may go up as well as down, daily). So on that basis for my 20 elec I get about 15p - 20p equivalent.

Either way, it seems fair to say that really it won't make much difference in my bills, all else being equal and assuming my home is fairly "standard".
 Air source heat pumps - Dog
This is a highly-insulated new build 3 bedder with an EPC of B and an ASHP.

Energy cost over the last 12 months is £1200. That's the total energy cost as we're all electric.

Previous 3-bed house (the one I showed you) was £900 on electric + LPG boiler + coal + logs etc.

I don't 'do' kWh stuff, I leave that to Man o'tea.

I've read about them being noisy - shoe menders!
 Air source heat pumps - Dave
I’ve got 2 air/air heatpumps in the house, and one in the workshop. We’ve got no gas here (sweden) so no comparison. However, one thing to be aware of is repair problems.

Heat pumps are big here, so there should be reasonable coverage for repairs and spare.

One of mine, a 7 year old Mitsubishi, recently quit working. Finally got a man out to look at it, and the flashing fault code. Fault seems to be the invertor card or the compressor. Both items about £900 each, plus fitting ( degassing, brazing in new part, regassing etc) and then the rest of the unit is still getting on a bit. Basically, its scrap. No one really wants to do the work, as its much easier and profitable to put in a new one.

These units are pretty complicated - inverter controlled fan, compressor and pump, electronic expansion valve, and a whole bunch of temperature and pressure sensors. Air/water even more so. My advice is reckon on a life of 10 years, and replacement of the outer part, and you wont go far wrong.
 Air source heat pumps - Manatee
Thought I'd written an essay on this on here recently but I can't find it so forgive any repetition.

We are heating a 213 sq. m. house with about 4000kWh per year of electric.

I know the 4000kWh is correct because the heat pump (ashp) has its own meter. Mitsubishi Ecodan 11kW.

I think the 4000kWh excludes the pumps, which aren't on that meter. I don't really know what they use, I suspect up to 200W when they're running. There are two main ones, one for upstairs, one downstairs for the underfloor heating (UFH). At the moment the ASHP is running about 20-25% of the time, that could be 75% when it's freezing outside. So you could probably add up to 10% to the heating cost.

The heating is 'on' 24/7 (it was off for Jun/July/August/September and about 9 days of October). Downstairs is at about 22C, upstairs probably 19C.

We are all-electric now and in the 12m. to 30 October we used 8800kWh in total. We have MVHR. The house is well sealed, and well ventilated. The MVHR claims to recover 90%+ of the heat we put in to the exhausted air. It supplies and removes a volume of air equivalent to a houseful about every 2.5 hours. It runs 24/7 and probably uses <1kWh per day - in theory it should be recovering quite a bit more energy than that which will be reducing the heat input requirement.

We have no solar PV. Electric wasn't 35p/kWh when we took that decision!, partly because we would have to put them on the front facing roof which has nice clay tiles on it. If I could go back in time I would probably use slate and PV tiles.

I assume you have rads. All ours is UFH. The flow temperature for heating is around 34C at the moment, hence the floors, whilst not clap cold, don't feel warm as they are below blood temperature (this is a disappointment to my wife!). The flow temperature follows a weather compensation curve, and goes up (to a maximum of 40C) when the outside temperature goes down. Flow temp for hot water is higher - I have the tank at 48C which is why we have a 300L tank. We have never run out of hot water yet!

You might be using a boiler temp of 65C or even higher. If you swap for a heat pump at 45-50 max, your rads might not be big enough. We can have much lower flow temp because in effect we have very large rads.

Note that the ASHP maximum output is only 11kW, much lower than the typical gas boiler in a typical semi half the size with a 30kW boiler. The heat loss calculation for the house IIRC was about 6 -7 kW so the ASHP has enough output to keep up BUT it does not have the grunt to warm the house up from cold in an hour or two especially with UFH which has high latency. Having the heating off when you are out all day doesn't work. When the weather went colder in October I was watching the forecast and put the heating back on a couple of days before.

There's another reason for running it continuously which is that heat pumps are more efficient with lower flow temperatures. I can raise the flow temperature which would shorten the on-time, but it would use more energy overall. Heat pumps have an on/off overhead too so short cycles are not good.

A heat loss calculation will answer your questions substantially. You'll need one for the design anyway. Have you an energy certificate? Ours, as a touchstone, is B/84.

An older house can be a challenge if the heat loss is high because heating the house 24/7 will use a lot of energy. With rads and a higher flow temp it might be possible to make more use of off periods or night-time temperature setbacks. I don't bother with a setback, I just keep the bedrooms a bit cooler than the living rooms.

Hope some of that helps.

The draughty 1950's bungalow we demolished to build the house used 27,000kWh of gas annually and 7000kWh of electricity (actuals for 2017 or 18, I can't remember which).

P.S. - the outside unit is not noisy! I expect the cost this year to be about £2600. We seem to use quite a bit for other stuff.
Last edited by: Manatee on Mon 20 Nov 23 at 18:10
 Air source heat pumps - Manatee
Should be clear, the £2600 is the total bill. Heating and HW will be about half that.
 Air source heat pumps - bathtub tom
I've heard reports they can become noisy. I suppose the bearings wear in time.
 Air source heat pumps - smokie
Thanks. There's a lot to think about!

I suspect your place is 1) larger 2) much better insulated and less draughty and 3) better designed all round for ASHP. I also expect that you keep your house much warmer than we do, in general, because I am tight with gas and we put up with a fair bit of coolness before putting the heating on. Our lounge was a bit over 16 earlier this evening!!

My gas over the 12 months was 5,400 kWh My electricity 10,334. I do have a modest number of panels which generated 2721 kWh in the 12 months, much of which we used as when it is generating but we're not consuming it, it sends the spare off the heat the hot water tank.

I don't yet have a COP I think it's something I can employ someone to do for not very much but I feel they may come up with some fairly expensive mods to achieve a decent figure.

It is def feeling to me that it would not be an economically good decision to go with one but I'll wait and see how the survey goes. It'd also be good to hear experiences from someone who's was converted rather than built for it.

Once again, thanks for the info
 Air source heat pumps - Manatee
Yes it's fairly well insulated (as anything of recent build must be), and because we have mechanical ventilation it's quite well sealed. I mentioned the heated area, in sq.ft. it's around 2300.

COP to heat pump people means coefficient of performance, which is (heat energy produced)/electrical energy consumed) for the heat pump. The design assumption for mine was about 3.6, it's mostly a function of the 'efficiency' of the heat pump rather than the house. I don't know what mine is. The heat pump controller implies it's only about 2 but that is clearly wrong - it's some sort of estimate because there is no heat meter on my system. I know it overstates the energy used because it 10% higher than the actual electricity meter on the supply. I'm pretty sure it underestimates the heat output by a lot.

My wife would not put up with your temperatures I'm afraid. I'm running it about a degree warmer than last year which seems to have stopped the evening grumbling. The wall stat in here shows 24.5 at the moment, a thermometer on the table I'm sitting at shows 21.7 which is what I go by. I could calibrate the thermostats but that would only make her think it's colder so I won't.

It's 8 degrees outside just now. If the sun were to come out the heating would be off for the rest of the day. We face SW and the solar gain is very noticeable even though the windows are not large on that side of the house (deliberately so).

I assume they will give you the detail behind the quote. That in itself should answer a lot of your questions.

If you can live with such low temperatures then it shouldn't be expensive to run. Bit don't do it to save money, because you almost certainly won't. Even if you cut your energy requirement to 1/3.6 * what it is now, if electric costs 3.6 times as much as gas per kWh then the cost will be similar. There is a profit opportunity in generating your own solar PV but if you are managing to use most of that then not so much.

I'm pretty happy. The house is never cold and the bill is manageable. I claimed the old renewable heat incentive which wasn't as generous as the current subsidy, it pays me £165 a quarter for 7 years so my net energy cost this year, without the cost of living payments, will be under £2,000.
 Air source heat pumps - Terry
There are some very basic points:

The price per kwh for electricity or gas means there will be little difference currently in running cost between gas heating or electricity with a heat pump.

None of us have a crystal ball - but it is how the relative price of electricity and gas change over time which will impact comparative costs.

The better insulated your house is the lower the bills will be. Manatee with a very recent build to high standards will be materially more efficient than my 1980s build.

Spending money on better insulation and heating controls may give a greater return than changing the heating system.

The higher the temperature set, the higher the bills will be irrespective of the fuel or heating method used.

We have recently moved. House has conventional gas CH/HW. The boiler, although old, is reasonably efficient and in good order. The radiators are served by 8mm pipework - the thermostatic valves and/or the pipes are not all working properly.

Rather than wait for failure and then make a panic purchase, the following is being investigated:

- air source multi split heat pump
- internal fan units to all main room providing both heating and aircon
- rarely used rooms may use electric panel heaters to save on full installation cost
- hot water by ecodan type system
- system would allow for much more responsive than hall and radiator thermostats
- remove all radiators to liberate usable space

Just need to cost it properly and decide on timing!
 Air source heat pumps - CGNorwich
I recently stayed in a house in Canada with air to air heat pumps. The fan noise would deter me from considering such a system. Found it very irritating It is after all just the same as having an air conditioner going all the time. Circulation of dust was also a problem

If I had to convert from gas I would go with an air to water heat pump and keep the existing radiators perhaps increasing thier capacity as necessary
 Air source heat pumps - smokie
Yes that's the system being proposed CGN. The Octopus price apparently includes replacement of any inadequate rads and anything else the system may need.

I remember viewing houses back in the 80s around Harlow new town (as it was then) and loads of them had warm air heating. Didn't like it then and nothing has changed that :-).
 Air source heat pumps - Bromptonaut
>> I remember viewing houses back in the 80s around Harlow new town (as it was
>> then) and loads of them had warm air heating.

We had it in the first house we owned (initially rented) when we moved up here from Watford in 1990. Pretty much the entire estate was built with Gas Warm Air CH. It was a bit noisy and, until got double glazing, temperature in the lounge was up and down like a fiddler's elbow but it was incredibly quick to warm up a cold house.

Previous owners had fitted a louvre door between the lounge/diner and hallway, presumably to address cold spots.

We lived with it for eight years.

Still available new or if you want it or to upgrade:
Last edited by: Bromptonaut on Tue 21 Nov 23 at 18:55
 Air source heat pumps - CGNorwich
My early seventies built house in Norfolk had a primitive hot air system. A brick cupboard in the kitchen held two paraffin fuelled Husqvarna oil stoves fed by a communal tank that supplied the whole estate.

One stove had a water jacker and supplied hot water and fed a radiator in the bathroom and bedrooms The other was to supply hot air for heating . Lighting them was a bit tricky as they had to primed with methylated spirit like a primus stove.

When the large heating stove got going it would supply a tremendous amount of heat which warmed the kitchen and lounge area by vents in the wall.

I remember a Manuel moment when whilst lighting the stove I spilt the methylated spirit which combined with some spilt paraffin and an old newpaper ignited in a wall of flame. I slammed the fire proof door shut and closed all the shutters to stop the smoke spreading. Modern heating is so much easier to manage
 Air source heat pumps - Clk Sec
>> I remember viewing houses back in the 80s around Harlow new town (as it was
>> then) and loads of them had warm air heating. Didn't like it then and nothing
>> has changed that :-).

We had warm air central heating in a new build property we moved to in the late 70s. Some of our neighbours were quick to have the system ripped out and replaced by radiators.

We reluctantly put up with it for a few years until we moved elsewhere, but would never have it again.

 Air source heat pumps - Manatee
The main problem with blown air electric now would be the cost of heating with direct electricity.

My grandparents ended up in a council bungalow with blown air heating. They loved it, basking in what felt like 30 degrees, and it warmed up from cold in minutes.

Constant low temperature UFH is great, but it's undetectability takes a bit of getting used to. The sensation of cosiness that one gets from an identifiable heat source is absent. Much easier to feel one is being warmed when one is colder on one side than the other. That's the only way I can describe or explain it. We are used to it now.
 Air source heat pumps - Robin O'Reliant
>> I remember viewing houses back in the 80s around Harlow new town (as it was
>> then) and loads of them had warm air heating. Didn't like it then and nothing
>> has changed that :-).

Early seventies I sold that door to door for about six months. That was after a spell selling screens you fitted on the front of your black and white TV to turn the picture into colour. It did too, just not the colours they should have been and not on the right part of the screen.
 Air source heat pumps - Dog

 Air source heat pumps - sooty123
Interesting article, I wondered if you overlaid electricity prices over up take of ashp they might related? I think Scandinavian countries have a large proportion of their electricity from nuclear power?
 Air source heat pumps - Bromptonaut
>> Interesting article, I wondered if you overlaid electricity prices over up take of ashp they
>> might related? I think Scandinavian countries have a large proportion of their electricity from nuclear
>> power?

Some of them, Norway sticks in my mind, have a lot of hydro-electric too.

One of the things that sticks in my mind from the EU referendum was the Norway model for being 'both in and out'.

At the time the EU was trying to reduce dependence on electricity for domestic heating with Directives to force states down that road. Norway, where hydro electric made electricity cheap 24/7/365 and widely used for heating, would be bound by the Directive but have little say in its framing and implementation at significant cost.

In the end the French saw it off as they also have, or had then, massive non stop power from Nuclear.
 Air source heat pumps - smokie
I've spent an hour or so ding some reading and some sums.

It seems, with energy prices where they are right now, that this year's gas might cost me about £500.

If I use they formula from the Octopus page that comes out about £1200, minus about £100 standing charges.

So it is a little over double. I am a reasonably light user of gas (I keep it cold here! But we also have a high-ish efficiency boiler). I'm not sure a heat pump is for me at the moment! Had I not changed the boiler less than three years ago it might have been different... and if they pump up the gas prices to encourage peoiple off then the equation will change.

Thanks for the inputs.
 Air source heat pumps - Rudedog
Can I ask how noisy they are?

When I set off to work at 6.30 it's relatively quiet but recently I've noticed a low level humming sound almost like a load of bees coming from a refurbished house opposite me and just wondered if it might be a heat-pump.

Quite noticeable at that time of the morning.
 Air source heat pumps - bathtub tom
See my post Mon 20 Nov 23 22:27

"I've heard reports they can become noisy. I suppose the bearings wear in time."
 Air source heat pumps - Zero
They should be between 40-60db when working properly, slightly less noisy than a gas boiler at full blast However the gas boiler is indoors, isnt always at full blast, so you dont hear it outside like the heat pump.
 Air source heat pumps - Manatee
People say they are noisy so I have to believe some are, but I am never aware of ours (11kW Mitsubishi Ecodan) unless I stand next to it. The guy next door has a ground floor bedroom window about 6 metres away from it and says he never hears it, but he is 84.

I am aware of the hum of pumps from the 'airing cupboard' that houses the 300L tank and other gubbins including the upstairs manifold. With the door shut it gets quite warm in there so I usually leave it open to circulate a bit of heat. I have to shut it if someone is using the bedroom opposite. That's about it.

The Potterton gas boiler on the wall in the kitchen of the rental we lived in for 3 years was a lot noisier.
 Air source heat pumps - Dog
Our Daikin Altherma isn't noisy. The Grant oiler we had in the olde Cornish cottage sounded like a Saturn V rocket taking orf.

The only noise I experience, is from the Grundfos pump, which is in a room (along with the water tank) directly under my bedroom!!

I've read that I could remove the pump (the heat pump has its own) along with the buffer, but I wouldn't do that.
 Air source heat pumps - Fursty Ferret
I think that as long as it's not wall-mounted you'll be fine. I have a smaller air conditioner "heat pump" unit on my house and while it's silent from outside, the vibration tends to resonate through the walls.
 Air source heat pumps - Dog
This is the YouTube where I came across the idea of removing the buffer tank and Grundfos pump.

He uses antifreeze valves instead of Glycol, which he says, makes the system more efficient:
 Air source heat pumps - Dave
Its amazing how complicated they make things just to eek out a percent or two of efficiency. Reminds me of modern cars, where a little better consumption and cleaner emissions comes with a hefty price a little later down the road. Maybe better to have a slighty dirtier system, but save on emmissions by having to junk and replace later on, like my Mitsubishi pump.
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