Air-source heat pumps - are they good/crap?
Discussion
I'm wondering whether ASHP would make sense for me?
4 bed 1960's dormer bungalow in Cornwall. Block construction, insulated cavities.
No mains gas, so we have a Worcester system oil boiler, rated at 15kw. Modern radiators, 15mm pipework.
We get through about 850 litres of oil a year on average, so that's around 8500 kwh.
Boiler isn't plumbed for hot water - we have a separate immersion heater which is run at the off-peak Octopus Go rate, plus electric showers.
The reason I'm considering changing is the oil boiler is 20 years old, and the oil tank is starting to show signs of cracking. A new tank would need to be resited, as the current position is non-compliant.
Would an ASHP work for us, and how would it compare in running costs at today's prices?
4 bed 1960's dormer bungalow in Cornwall. Block construction, insulated cavities.
No mains gas, so we have a Worcester system oil boiler, rated at 15kw. Modern radiators, 15mm pipework.
We get through about 850 litres of oil a year on average, so that's around 8500 kwh.
Boiler isn't plumbed for hot water - we have a separate immersion heater which is run at the off-peak Octopus Go rate, plus electric showers.
The reason I'm considering changing is the oil boiler is 20 years old, and the oil tank is starting to show signs of cracking. A new tank would need to be resited, as the current position is non-compliant.
Would an ASHP work for us, and how would it compare in running costs at today's prices?
You’re in a similar position to me in that you have an old heating system which needs replacing…in my case gas boilers (more than one of them) I think it is an “easier” decision. I would have to spend several thousands pounds getting new boilers which makes the upfront cost of heat pump slightly less painful. If you get a heat pump any work you get done to the rest of your heating system is VAT free, this is quite a big advantage for me as 2/3 of our house has a single pipe heating system which is incredibly inefficient and needs upgrading at the same time.
They key to a successful heat pump installation is not just the fabric of your home and existing heating system but also the quality of the installation…there are quite a lot of variables in system set up which can make a big difference. Broadly in terms of economics you would want a system with a COP of 3 to 4 which is what I have been told is possible in out house which is older than yours…no cavity walls.
I have found this You Tube channel very educational. He’s a heat pump installer, talks a lot about the way he sets systems up and installs them.
https://youtu.be/qxtbHYf0OT0?si=41S0w3EzffiYaJMP
Heat Geek is another YouTube channel where you can get a lot of information from.
They key to a successful heat pump installation is not just the fabric of your home and existing heating system but also the quality of the installation…there are quite a lot of variables in system set up which can make a big difference. Broadly in terms of economics you would want a system with a COP of 3 to 4 which is what I have been told is possible in out house which is older than yours…no cavity walls.
I have found this You Tube channel very educational. He’s a heat pump installer, talks a lot about the way he sets systems up and installs them.
https://youtu.be/qxtbHYf0OT0?si=41S0w3EzffiYaJMP
Heat Geek is another YouTube channel where you can get a lot of information from.
Jambo85 said:
I don’t mean to be a pedantic but I don’t think the house is a variable in the CoP? More the heat pump itself and the local climate, no?
That and you want the heat pump to be running most of the time at a capacity where it’s achieving that COP range. Ie if it’s undersized it’s running flat out which isn’t great for efficiency. Same as if it’s oversized, it’s spending at lot of time throttled back/short cycling outside of it’s optimal operating range.Assuming it was possible to achieve a COP of 3 (averaged over the heating season), a heat pump would be slightly more expensive to run at current prices. Oil is costing about 7.5p per kwh. Electricity is 27p on Go, so 9p per kwh at a COP of 3.
I'm getting quotes for tank replacement, and for changing to ASHP.
I'm getting quotes for tank replacement, and for changing to ASHP.
clockworks said:
Assuming it was possible to achieve a COP of 3 (averaged over the heating season), a heat pump would be slightly more expensive to run at current prices. Oil is costing about 7.5p per kwh. Electricity is 27p on Go, so 9p per kwh at a COP of 3.
I'm getting quotes for tank replacement, and for changing to ASHP.
It's also worth noting that the flexibility of oil means you can just heat your house when you want it whereas heat pumps generally need to run steady temperatures.I'm getting quotes for tank replacement, and for changing to ASHP.
If your house is very well insulated that's less of an issue but keeping an older house at 21 degrees (or whatever) 24 hours a day is likely to prove expensive regardless what heating source you use.
Snow and Rocks said:
It's also worth noting that the flexibility of oil means you can just heat your house when you want it whereas heat pumps generally need to run steady temperatures.
If your house is very well insulated that's less of an issue but keeping an older house at 21 degrees (or whatever) 24 hours a day is likely to prove expensive regardless what heating source you use.
Why do heatpumps need to run at steady temperatures? Is it because they take longer to reheat a room back up to the required temperature?If your house is very well insulated that's less of an issue but keeping an older house at 21 degrees (or whatever) 24 hours a day is likely to prove expensive regardless what heating source you use.
I have an Evohome setup, so rooms are only heated as required:
Kitchen/diner, workshop and study at 20 degrees during the day
Lounge at 21 degrees in the evening
Bedrooms at 18 degrees first and last thing.
Bathroom at 20 degrees for the evening showers.
Hallway at 17 degrees while we are awake.
At other times, they are all set for 10 degrees.
This saves about 30% oil consumption over using TRVs and a single 'stat/programmer in the hallway.
Would this not work with a heatpump?
Heat Pumps run at lower temperatures than gas/oil boilers so they don’t get radiators as hot so “on/off” heating doesn’t work for them…that said there are now high temperature heat pumps which operate at temperatures closer to that of traditional boilers.
I am looking at a heat pump with solar/pv as well. In my mind that is when they really start to make sense, Obviously there is a greater initial outlay but you can be running your heating system in the autumn and spring for free and even in winter will get some PV but the batteries mean you can charge overnight at 7.5p per kWh.
I am looking at a heat pump with solar/pv as well. In my mind that is when they really start to make sense, Obviously there is a greater initial outlay but you can be running your heating system in the autumn and spring for free and even in winter will get some PV but the batteries mean you can charge overnight at 7.5p per kWh.
gangzoom said:
jonathan_roberts said:
I’m not trying to sell ashp but any of these scare stories you hear appear to be from poor understanding, or under-specced poor installations rather than actual problems with heat pumps themselves. So far ours has been flawless.
Actually your energy use in winter looks incredible compared to just our electricity usage just for the house+EV charging WITHOUT heating. That's with our house having a PowerWall and solar PV. I would say your experiences of overall energy usage is totally different from others (certainly mine). Add in energy needed for an ASHP versus gas, I suspect our electricity bill for winter would be double yours. You data simply confirms what I fear, ASHP only works if you build your house for it. I personally rather not build a house design around the heating source/bill.....
Better insultation however is the way to go regardless, the house use to visibly leak heat in winter, you could see bits of dust going up into cracks in the roof/celling when the heating was on full blast and it was freezing outside!! I'm hoping our rather extreme approach to improving insulation will mean heating bills for winter 2024 will be alot lower....The real irony is ofcourse global warming makes heating bills less worrying.....providing you don't live in a flood zone
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I don’t think you can compare apples for apples either (UK vs Austria) temperature wise, and brand new house with 25cm insulation jacket vs English build with sieve-like windows. In winter the house is kept at 22 degrees (my wife likes it warm enough to walk around with no clothes on). I consider it to be low usage considering the low temperatures and the internal house temp.
There’s no doubt I could lower the bill, but then I’d have to change my wife.
jonathan_roberts said:
That screenshot is just the ASHP. Our total usage is nearer 13000kwh with 2 Teslas and me working from home.
I don’t think you can compare apples for apples either (UK vs Austria) temperature wise, and brand new house with 25cm insulation jacket vs English build with sieve-like windows. In winter the house is kept at 22 degrees (my wife likes it warm enough to walk around with no clothes on). I consider it to be low usage considering the low temperatures and the internal house temp.
There’s no doubt I could lower the bill, but then I’d have to change my wife.
I don’t think you can compare apples for apples either (UK vs Austria) temperature wise, and brand new house with 25cm insulation jacket vs English build with sieve-like windows. In winter the house is kept at 22 degrees (my wife likes it warm enough to walk around with no clothes on). I consider it to be low usage considering the low temperatures and the internal house temp.
There’s no doubt I could lower the bill, but then I’d have to change my wife.
Very similar to my usage, a quick check confirms I used 13,266 kWh in the last 12 months in a new 4-bed house over three storeys with presumably similar construction to yours.
No EV (yet, one on the way) but offspring who don’t seem to know what an off switch is. My son’s gaming PC in particular seems to run almost constantly and probably accounts for about 10% of consumption!
Anyway, the average monthly bill is about €180. Yes, I could trim it a bit but as you say that would impose lifestyle changes so I’m okay with that.
loudlashadjuster said:
jonathan_roberts said:
That screenshot is just the ASHP. Our total usage is nearer 13000kwh with 2 Teslas and me working from home.
I don’t think you can compare apples for apples either (UK vs Austria) temperature wise, and brand new house with 25cm insulation jacket vs English build with sieve-like windows. In winter the house is kept at 22 degrees (my wife likes it warm enough to walk around with no clothes on). I consider it to be low usage considering the low temperatures and the internal house temp.
There’s no doubt I could lower the bill, but then I’d have to change my wife.
I don’t think you can compare apples for apples either (UK vs Austria) temperature wise, and brand new house with 25cm insulation jacket vs English build with sieve-like windows. In winter the house is kept at 22 degrees (my wife likes it warm enough to walk around with no clothes on). I consider it to be low usage considering the low temperatures and the internal house temp.
There’s no doubt I could lower the bill, but then I’d have to change my wife.
Very similar to my usage, a quick check confirms I used 13,266 kWh in the last 12 months in a new 4-bed house over three storeys with presumably similar construction to yours.
No EV (yet, one on the way) but offspring who don’t seem to know what an off switch is. My son’s gaming PC in particular seems to run almost constantly and probably accounts for about 10% of consumption!
Anyway, the average monthly bill is about €180. Yes, I could trim it a bit but as you say that would impose lifestyle changes so I’m okay with that.
In any case, and back on topic, I’d happily recommend an ashp but only within certain parameters that I know it works. Though I would say that the climate in England is fairly ideal for them to run efficiently.
jonathan_roberts said:
That screenshot is just the ASHP. Our total usage is nearer 13000kwh with 2 Teslas and me working from home.
It’s that 13,000kWh of grid import, if so that’s a crazy amount of energy usage! If your ASHP energy consumption is the same as our total energy usage including charging an EV, I honesty don’t see the appeal, mains gas is essentially the same cost. gangzoom said:
jonathan_roberts said:
That screenshot is just the ASHP. Our total usage is nearer 13000kwh with 2 Teslas and me working from home.
It’s that 13,000kWh of grid import, if so that’s a crazy amount of energy usage! If your ASHP energy consumption is the same as our total energy usage including charging an EV, I honesty don’t see the appeal, mains gas is essentially the same cost. Cars 5.5k kWh
Living and working (cooking, lighting, etc etc? 3.5k kWh
Our last house had gas with UFH, and the cost to heat was far more expensive €240/month (this was before the energy crisis) and the heating was on a thermostat and never consistently warm. If you left it on through the night it would just waste so much cash. It’s not the same as heat pump setup. Far worse, in fact.
The point I’m not sure people get is that a well set up heat pump maintains stable temps during cold spells at an average price this year of €80/month (or less my new tariff is €0.11/kwh all in this month). I checked by the way and 15,000kwh of gas at the moment is best offer €1293.83. I’m skeptical that I can heat for 15,000kwh, I’d say it would be more like 25,000kwh.
Mains gas “may” in theory cost me the same, but my experience of gas is that it would be far more expensive for the level of heat my wife likes.
I have always said in all my posts that I don’t think retrofitting a heat pump is a good idea unless you go to serious expense of insulating and underfloor heating. But, what I do think is that you’d be mad to install a gas boiler in a new build.
gangzoom said:
It’s that 13,000kWh of grid import, if so that’s a crazy amount of energy usage! If your ASHP energy consumption is the same as our total energy usage including charging an EV, I honesty don’t see the appeal, mains gas is essentially the same cost.
With electricity at 28p/kwh and mains gas at 7p, that's exactly what it is if your HP is running at 400% efficiency. Which is just about best case. You might find a few pence here and there by shopping around or using your heating in off peak times but it will take you a long time to recoup your investment. jonathan_roberts said:
But, what I do think is that you’d be mad to install a gas boiler in a new build.
I suspect in the UK the number of new builds with access to mains gas having an ASHP installed instead must be single digit percentages. I personally think you would be mad to go down the ASHP route out of choice if you have access to mains gas. I cannot see the UK government actually following through on their plans to 'ban' gas boilers in my life time. clockworks said:
Assuming it was possible to achieve a COP of 3 (averaged over the heating season), a heat pump would be slightly more expensive to run at current prices. Oil is costing about 7.5p per kwh. Electricity is 27p on Go, so 9p per kwh at a COP of 3.
I'm getting quotes for tank replacement, and for changing to ASHP.
Id stick with oil for now. If you do replace a tank buy a big one, ie 2500 litres (max permissible in a domestic setting) so you can buy when oil price is low.I'm getting quotes for tank replacement, and for changing to ASHP.
As government becomes ever more desperate to get you to have a heat pump, the money thrown at you will keep going up. Might as well wait until they more or less pay you to have it, then spend your own money upgrading.
Plus of course, electricity prices are only going to go one way. Oil is a bit more difficult to control, and if they get stupid with , just run it on diesel instead.
Cheib said:
Heat Pumps run at lower temperatures than gas/oil boilers so they don’t get radiators as hot so “on/off” heating doesn’t work for them…that said there are now high temperature heat pumps which operate at temperatures closer to that of traditional boilers.
I am looking at a heat pump with solar/pv as well. In my mind that is when they really start to make sense, Obviously there is a greater initial outlay but you can be running your heating system in the autumn and spring for free and even in winter will get some PV but the batteries mean you can charge overnight at 7.5p per kWh.
It only makes sense if you ignore the capital outlay for all that stuff.I am looking at a heat pump with solar/pv as well. In my mind that is when they really start to make sense, Obviously there is a greater initial outlay but you can be running your heating system in the autumn and spring for free and even in winter will get some PV but the batteries mean you can charge overnight at 7.5p per kWh.
monkfish1 said:
Plus of course, electricity prices are only going to go one way. Oil is a bit more difficult to control, and if they get stupid with , just run it on diesel instead.
Surely the reverse is true and electricity prices will tumble as renewable green energy comes on line, while gas will go up as resources are depleted? Government plans always go as intended!gareth h said:
Andeh1 said:
We're 10 months in with our ASHP in a good size sprawling bungalow, highly insulated. A mixture of octopus cosy tariff (averages out to 22p/kwh from our usage) and an ASHP running at about 3.4COP gives us an energy cost of about 6.5p/kWh.
However.... The 300L cylinder and 52degree DHW is the negative, with a large household we do have to compromise on hot showers. I shower last and it's luke warm at times, and due to the peak rate between 4 and 7pm in our tariff I'm too stingy to pay to reheat it during that period. We have an insulated recirculation loop which draws the heat out as well.
Is 52 deg all you can achieve or is the temperature that has been set? However.... The 300L cylinder and 52degree DHW is the negative, with a large household we do have to compromise on hot showers. I shower last and it's luke warm at times, and due to the peak rate between 4 and 7pm in our tariff I'm too stingy to pay to reheat it during that period. We have an insulated recirculation loop which draws the heat out as well.
It's default installation was set at 50 degrees and an automatic reheat of it dropped below 40 degrees I think it was. It takes about 45mins to fully reheat from cold, so in its default mode you'd struggle to run out of hot water unless really pushing it.
For our usage and the super cheap tariff during set periods I disabled default and just had it hammer the hot water during off peak, at the detriment of us showering during peak and last shower being risk of luke warm only.
That being said, Insulated house, ASHP and flexible tariff means we're probably going to settle near £150 for total running costs, Inc dish washer every night, washing machine daily and tumble dryer couple times a week.
To give an example, solar, ashp and cheap tariff meant I put nearly 1000L of hot water into paddling pools on the hot Saturday we had, cooked and had the air con going inside and it still cost us about £3 for the days usage.
JuanCarlosFandango said:
monkfish1 said:
Plus of course, electricity prices are only going to go one way. Oil is a bit more difficult to control, and if they get stupid with , just run it on diesel instead.
Surely the reverse is true and electricity prices will tumble as renewable green energy comes on line, while gas will go up as resources are depleted? Government plans always go as intended!Cheap energy would be a disaster for government as it will reduce control over the population. Plus of course, as supply of electricity fails to keep up with demand, well, we all know what happens to commodities in short supply. Getting cheaper isnt it.
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