Air and Ground Source Heat Pumps, are one of the most efficient forms of Electric heating that currently exists, and upto five times more efficient than a standard convector heater of the same rating.
Whilst Heat Pumps are still not yet efficient enough to compete directly with Gas Central Heating Systems, they are generally far cheaper than LPG and Oil based central heating (upto 60% cheaper in like for like systems), and five times cheaper than Electric Boilers and Underfloor heating. In addition, they offer more flexibility than storage heaters, and often produce far more usable heat. That is assuming that the outside air temperature isn’t too low, because a Heat Pump operates at its peak efficiency with external temperatures at around 6c to 9c, and becomes next to useless when its -5c to -10c
So, how much do Heat Pumps actually cost to run?. Well lets take some working examples.
First of all, its important that you shop around for the best Electricity Tariff for your region, Electricity costs vary drastically from region to region, and I have found prices ranging from 11p KW/H to 19p KW/H just by comparing prices in my own area!. Differences like this, can easily add up to a few hundred pounds per year, so shop around.
The cost of running also depends on the type of system and its Electricity Consumption, as well as how often its used, and how cold it is outside.
A 2.2KW Air Source Heat Pump based boiler will produce around 11KW worth of hot water for Radiators, and consume 2200 Watts from the mains. At a cost of 12p per KW/H, running this system would cost around 27p per hour in Electricity, or £2.11 for an 8 hour ‘running period’.
However a larger central system consuming around 11kw will be fairly expensive, costing around £1.12 per hour to run, however it will generate enough heat to warm an average sized 3 bedroom property.
You can use the following formula to work out the running cost as i’ve done in the above example
(kilo watt loading) X (number of hours running) X (electricity unit cost in pounds) = running cost per hour
And so:-
2.2 (kw) X 1 (hour) X 0.12 (electricity cost in pounds) = £0.264 per hour running cost
Compare this to an average cost of 11kw worth of hot water produced from an Heating oil powered central heating boiler, which would cost 61p per hour to run, or £4.93 for an 8 hour ‘running period’ (based on 56p per litre for oil).
As you can see, running the Heat Pump costs less than half of the price for producing the same amount of heat of an Oil fired heating system, and makes it a very viable option for those with LPG or Oil based systems.
Let’s also compare the cost of the 2.2kw Air Source Heat Pump, compared to 11kw worth of conventional convector heating used on the same 12p kw/h tariff.
11 (kw) x 1 (hour) x 0.12 (Electricity Cost in pence) = £1.32 per hour
So to run 11kw worth of conventional Electric Heating, against the 2.2kw drawn by the Air Source Heat Pump, would cost £1.05 per hour MORE
Remember to use the following formula to work out your own Heat Pump running costs
(kilo watt loading) X (number of hours running) X (electricity unit cost in pounds) = running cost per hour
Hello
I am sorry but I don’t undestand how you worked out the difference of £1.05 btw coventional and Heat pump.
Moreover according with your formula the 11kw of the Heat pump would cost 1.32£/h
How did you work out 1.12£/h in your previous example?
(….a larger central system consuming around 11kw will be fairly expensive, costing around £1.12 per hour to run, however it will generate enough heat to warm an average sized 3 bedroom property.)
Thanks
Hi, this article was written several years ago using the tariffs available at the time for comparison. Very recently (autumn 2021) those tarrifs have changed, radically and in the wrong direction!.
Gas currently costs around 4p (on a standard variable Ofgem protected tariff) and peak rate Electricity costs in excess of 20p per kWh and off peak around 12p per kWh on the same type of variable tariff. There may be some subtle variations and regional differences to the cost of peak and off peak rates given but that, I believe is the average. Even those currently on fixed tariffs are only months away from being put on the above mentioned tariffs when their fixed period ends.
Decent fixed tariffs for either energy are virtually non existent as of November 2021, and probably won’t be for several months or more. Suffice to say Electricity prices in the UK are probably going to continue to rise in bigger increments when the price cap is reviewed again than gas due to the fact we are still heavily reliant on Gas turbines to generate Electricity.
I’m not aware of any Electricity tariff for heat pumps which essentially gives an off peak tariff 24/7 or any currently much below the off peak figures I’ve used, and if they do exist they are probably severely limited in off peak duration and no doubt generally off set by peak rates of 25p – 30p per kWh.
You correctly state that a 11kw pump will heat a 3 bedroomed property, however so will a fairly modern, efficient 15kw Gas boiler, thanks largely to the fact that they get radiators hot and so can heat a room from cold quite quickly.
To use today’s rates, a 11kw heat pump using peak rate Electricity will consume 11 X 20p units per hour or £2.20 per hour. On a current off peak E7 tariff the same pump will consume 12p X 11 units or £1.32 per hour.
In comparison an equivalent 15kw input Gas boiler using gas at 4p per kWh will cost £0.60 per hour to run at any time of day, even a 22kw input Gas boiler will only cost £0.88 per hour.
My parents adequately heat their 3 bedroom 1939 built semi detached property with only loft insulation and double glazing from a 16kw boiler, so I’m confident that my estimate of 15 – 22kw for a modern Gas boiler is perfectly adequate for the task in most 3 bedroom houses.
A gas boiler will also modulate its output once the water circulating the heating system reaches the Temperature set on the boiler control so the hourly cost may well be even less than the calculation figures I’ve used as the boiler modulates the gas flow to its burners, but for calculation purposes I’ve assumed the boiler is running at its full gas input rating continuously and not taking any modulation into account.
However the fact it probably won’t still be burning 15kw of gas after the first hour or so when the radiators are up to temp and the water circulation temp has been reached should still be taken into account.
This is just a rough guide but it also doesn’t include the purchase and installation cost of a ASHP compared to a Gas boiler, plus the lower water temperature output from a ASHP of around 45c – 50c a temperature which when it comes to DHW often requires a boost using a 3kw immersion heater, for example if a family want hotter water for washing dishes, or an automatic cycle is carried out by the system to prevent bacteria growth for example.
Boosting the water temperature using an immersion heater for a bath or washing dishes for one hour on peak rate Electricity would be 3kw X 20p adding another 60p into the cost equation. Whilst a gas boiler with a boiler stat fitted or a combi would ensure DHW at around 58c – 60c all day long as part of its running cycle, and in the case of a combi will only heat the water required from the tap, and do it reasonably quickly with no need for any large heat store.
Suffice to say the lower radiator temperature which comes from a ASHP requires a greater level of building insulation to heat a property from “aired” radiators or UFH, making them unsuitable for most older properties.
I know several people with ASHP systems who have to run them 24/7 during the winter months as it takes so long to heat up the fabric of the building – especially where UFH is the primary source of heat whilst people I know with Gas central heating just use a timer to run the radiators for a few hours in the morning and then perhaps 5 or 6 hours in the Evening when they get in from work, or use a hive / Todo smart thermostat to set different temperature profiles based on the time of day, and an efficient gas boiler would react dynamically to these timed temperature changes in 45 mins to 1 hour, whilst a ASHP would, I suspect, take hours to make up a 4c or 5c room temperature difference between the house being unoccupied and occupied (for example).
So despite being several years old, I still believe the crux of the article to still be accurate when comparing the cost of running a ASHP compared to a modern gas boiler.
We’ll also gloss over the fact that a ASHP effectively becomes far less efficient below 0c and can in some cases even stop working in very low temperatures – perversely leaving you without heating when you need it the most on the coldest nights of the year and so bringing with it a greater reliance on plug in heaters and that immersion heater!.
I’ll close with the fact that the current topic of replacing gas boilers nationally with ASHP directly, in my opinion is absolutely ludicrous.
These systems probably work well in traditionally mild climates where it’s 10c – 15c all winter and their winter sunlight strong and plentiful enough to boost the ASHP output using solar and in Scandinavia where huge levels of insulation has been the norm in house building
for decades, but expecting ASHP to work in Scotland or rural Wales, in January where sunlight is rare and overnight temps regularly drop to -10c is delusional without massive investment in both the system and domestic levels of insulation, an investment I will add which millions of people simply don’t have or creating debt which many don’t want to take on.
Hi again
I am sorry I forgot to tell our electric taiff is 20.91p/kWh
I think tha’s important for the comparation
Thanks
So, an 11kw heat pump would cost 11x 20.91p (£2.31) per hour to run based on your current tariff of 20.91p per unit or kwh.
Even if the heat pump was a smaller size and rated at 7.5kw the running cost would still be 7.5 x £0.2091 (£1.56) per hour. And I suspect you would be struggling to space heat a typical 3 bedroom property from a heat pump much below 10kw given the very low water temperature they produce.
Alternatively, a modern 16kw gas boiler on a variable tariff protected by the current Ofgem price cap for Gas of 4.1p per kwh would cost 16 x £0.041 per kwh (£0.656) per hour, and you would also have hotter tap water into the equation without supplementary immersion heater use.
Even if the Gas boiler in the comparison was 50 years old and extremely inefficient, even running with 50% efficiency the hourly cost would still be £1.31 per hour.
If you have to use a 3kw immersion heater at any point alongside the heat pump, then that would cost 3kw x 20.91p = £0.627 per hour during the periods it’s heating water which is in addition to the running cost of the heat pump.
Electricity is always going to be more expensive than gas due to the fact that despite all of the hype surrounding renewable energy, and the £ billions spent on it, now that the coal fired power stations have been decommissioned we are still heavily reliant on using gas turbine generation for producing Electricity, so we have to purchase one expensive fossil fuel in order to burn it and generate another – Electricity!.
Also the COP of 4 and above that you see in the glossy brochures for heat pumps is generally quoted at their ‘ideal’ operating parameters usually 7c, but as it gets colder outside that COP efficiency figure will drop perhaps to just 2.5 when it’s -7c, whilst a modern gas boiler maintains its rated efficiency whether it’s 23c outside or -18c.
For heat pumps to ever be as cheap to run as Gas, then the Electricity kw/h cost will first need to drop considerably. Or better still a smart tariff introduced where the kWh cost of running the heat pump changes in relation to their reduction in COP efficiency as it gets colder outside.
However I can’t see that happening for decades, given the Ofgem protected kWh cost is currently around 21p per kWh and energy companies profess to be making a loss even selling at that price, so 10p per kWh or under isn’t going to happen anytime soon, even E7 off peak rates are currently well above that.
Hi
Thanks again for your exaustive reply.
However I am not sure you’ve received my previous email telling about my actual situation with LPG.
I am going to submit it again below asking if you would like give your notes.
Many thanks
Hi
Thank you for your exaustive answer.
Honestly I am not an expert on this matter so I had to read it few times to understand.
I understood that running a Gas system is still cheaper than ASHP.
I agree with you the current topic of replacing gas boilers nationally with ASHP directly, actually is absolutely ludicrous.
But as fossil fuel are destinated to run off in the future and anyway they are not evironmental friendly so I am looking around for alternatives.
So with the grant prospected by the governament for the ASHP maybe could be advantagious to change now.
However I can’t really work out how much would be the running costs of ASHP compared with actual system in our household.
So I would ask you if you could help with a comparation.
We are based in south Devon and hour house is a three beds new converted barn very well insulated.
We have UFH with a timed comby boiler which runs with LPG and the temperature of the water is max 35c. At the moment on these days the external T is btw 5c and 10c and to rise 2c in the morning the UFH take about 3h. Then thanks to the good insulation the internal temperature is stable all day long even though the house is north faced and not reallt sunny.
We are very wise in consuming (either for the environment and for the wallet) so we keep our living T around 19-20c and DHW 40c which for us is just enough to the comfort and to take a shower.
Last year round (Sep’20 to Aug’21) we’ve used 700l/LPG @ 0.3675£/l = 257.25£
So first of all I am wondering how an ASHP would work in our case.
For example: to keep the water temperature 45-50c does have to run all day long?
or Does the system require the installation of a tank to storage the hot water and then the ASHP switch on when needed?
How much roughly would be converting the system from LPG to ASHP.
Last question of course is how much roughly would cost to run th ASHP considering our standard of living?
I hope evryhing is clear and enough to make a comparation so your advise would be appreciate.
Thanks for your attention.
Kindly
Falco
Hi
I assume that you aren’t using any form of Electric Heating alongside the LPG system, and that figure you gave of £257.25 for 12 months worth of LPG use, represents your entire household heating costs?. If this is correct and nothing has changed in relation to your heating use currently, then I would most certainly stick with LPG for a while yet before making any changes or large investments in other forms of heating, as your Heating costs are extremely low based on the national average, and you are unlikely to better the equivalent of £21.44 a month for heating – which is what £257.25 annually, basically works out when calculated over 12 months.
Unfortunately using an ASHP is going to work out a LOT more than £21.44 a month / £257.25 per year to run. As they do have to work 24 hours during the coldest months in order to maintain the heat, paying £0.2091 per KW/H as you are for Electricity and running it 24 hours a day is going to cost a fortune to run. Saving the Environment is very honourable, but i’m not sure that you want to potentially far worse off in heating costs for doing so.
Besides it would be very difficult at this current time to imagine how running an Electric ASHP 24/7 was any better for the Environment than running your current LPG system at a low level ‘timed’.
Perhaps by 2030 the situation will have changed but in 2021 using Electricity as a cleaner form of energy is a misnomer at the moment, and is largely misrepresented by the number of Energy Companies touting Green Energy as being a thing. Regardless of what you may have been led to believe, currently in the UK anything up to 50% of our Electricity Requirements at any given time are generated by burning natural gas (CCGT) – which may be very slightly cleaner than Coal, but is not in anyway Renewable, and probably no better for the Environment than your LPG Boiler – so essentially all you will be doing at the moment is swapping one fossil fuel for another and paying a fortune for doing so whilst not actually changing anything in relation to your original goal.
I believe in the middle ages this kind of thing was called “selling indulgences!”.
The site below is very interesting, as it shows, in real time the demand on the UK National Grid, and all of the methods we are using to cover that demand. CCGT is Gas Turbine Generators and for huge amounts of time, it is the method producing the most energy!.
https://www.gridwatch.templar.co.uk/
Also, if you want to read about the cost of running a ASHP, then the blog page below is well worth a read as it documents the running cost of a Family who made the change from Oil Fired Central Heating to ASHP for pretty much the same reasons as you and gives a TRUE real world reflection of the cost of running it. I have no connection with the Authors, other than finding it a good source of information to quote or refer people to.
https://myhomefarm.co.uk/potential-air-source-heat-pump-running-cost-issue
All that I can suggest is that you continue to use your LPG System in pretty much the same way as you have done so for the past 12 months, as I don’t see any advantage to changing to Electricity in any form whilst we are still using Fossil Fuels to generate up to 50% of what we are consuming.
If Solar Panels are an option for you (although you mention lack of Sun in the position of the property so perhaps not), then these might be worth investigating to cover future ASHP requirements, but I certainly wouldn’t be investing in a ASHP whilst the Electricity costs are 20.91p per KWH.
Many many thanks.
Yes I can confirm I am not using any Electrical Heating along side the LPG. Just sometimes we use a little fan heater to warm up the bathroom when we take a shower. But this would run max 10min a time and just in winter time during the coldest days.
I am just a bit bewildered when you state that 50% of the Electricity Requirement in the UK is still produced by burning natural gas.
I wonder how certains Energy provider can declare they are supplying 100% green and renewable energy then. Are they just cheating to attract more clients?
If this the actual situation then I would really feel less guilty on using the LPG thanks of the fact being considarate in consumption beyond saving money (as you said) would incure to be cleaner than running an ASHP all the day long.
Anyway thank you so much for your advise and attention.
All the best
Unfortunately we are a long way from having 100% renewable energy, even with the gales forecast this weekend, renewable will only produce 30% of our energy requirements, and unless we suffer constant 24/7 gale force winds for the future, then that figure will drop back to around 10% once the windy spell passes.
If you think about it, if renewables really provided the bulk of our energy then why are Electricity prices so high, renewables are free beyond the cost of running the infrastructure, so if they were the strongest factor then Electricity prices should be going down instead of up!. The fact they have increased to almost record levels is because we use Gas – which is also increasing in cost, and that link is no coincidence.
Some energy companies engage in “greenwashing”. A quick Google of the term will explain all.