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Heat Pumps v Gas Heating

December 20, 2015

By Paul Homewood 


h/t Joe Public


One way to decarbonise domestic heating, which the government has been pushing for a while through its RHI scheme, is the use of heat pumps. Joe sent me the link to the  Energy Saving Trust website, which offers advice.


According to them, air source heat pumps can cost in the region of £7000 to £11000, and offer the following savings:




Rather dishonestly, the Trust use inefficient non-condensing boilers as the benchmark, even though very few households have them anymore. Even then, there is no financial justification for switching from gas, especially as the Trust point out that heat pump maintenance is not factored in.

There are also question marks over whether heat pump technology can cope with water heating, or very cold weather, thus necessitating supplementary systems.


The story is similar with ground source pumps, which are dearer, but offer better fuel savings. These can cost between £11000 and £15000, with fuel savings of:



  1. Joe Public permalink
    December 20, 2015 5:11 pm

    That air-source HP page disingenuously states:

    “Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. During the winter they may need to be on constantly to heat your home efficiently. You will also notice that radiators won’t feel as hot to the touch as they might do when you are using a gas or oil boiler.”

    The radiators & pipework in the home are sized for set flow-and-return-temperature-differentials. They chose to use the ‘Gas older (non-condensing)’ boiler category to maximise the apparent savings vs heat pumps. It is precisely those older non-condensing boilers which have the radiators & pipework sized for the greatest flow-and-return-temperature-differential. Consequently, a heat pump won’t achieve the desired internal comfort temperature.

  2. December 20, 2015 5:14 pm

    The question is how efficient and green are the new alternatives of energy? Are they really as green as their supporters say, or would it be better to do more research in these fields? I’m talking about solar panels, wind farms and offshore wind farms.

    • Joe Public permalink
      December 20, 2015 5:39 pm

      ‘Efficiency’ is only part of the equation. Dependability is arguably more important.

      Solar & wind are unpredictably intermittent, and, incapable of supplying 24/7.

    • saveenergy permalink
      December 20, 2015 6:17 pm

      Capacity factors for UK ‘renewable technology’s’ –

      Biomass = 52%
      Hydro = 40%
      Wind offshore = 31%
      Wind on land = 23%
      Solar PV = 9%
      Tidal = 7%
      Wave = 4%

      Nuclear = 67%.
      Gas for electrical Generation ~ 70%
      Gas point of use heating 96-98%

      UK ‘renewable technology’s’ Outputs

    • December 20, 2015 8:10 pm

      “Green” adverts for heat pumps and solar thermal never seem to mention the fact that it is anti-freeze that is being pumped onto your roof and into your soil.

  3. J Martin permalink
    December 20, 2015 5:47 pm

    I have an old non condensing gas boiler which was 70% efficient when new 30 years ago presumably less than 50% efficient now. As HM Gov is offering up almost enough money to nearly pay for an air source heat pump over 7 years I looked into it briefly.

    There is an online form you can fill in that tells you how much money they will pay you. One of the factors involved is the number of bedrooms, so the bigger your house the more money HM gov will pay for installation of an air source heat pump.

    If I had a slightly larger house I might have looked into it further as I quite fancy the idea. But it looks as if a brand new 96% efficient combi boiler is what I need, at a stroke halving my central heating bill.

    I’m not convinced by the governments green credentials, why did I have to pay VAT on the triple glazing I just put in the back if the house, front yet to be done. Shouldn’t they be encouraging energy saving ?

    As I am looking to upgrade from an inefficient boiler to one which is twice as efficient, then why don’t they encourage that by lifting VAT on such improvements ?

    • December 20, 2015 6:57 pm

      To paraphrase DelBoy, “Saving the planet is nice, but business is business”!

    • Joe Public permalink
      December 20, 2015 7:15 pm

      “I have an old non condensing gas boiler which was 70% efficient when new 30 years ago presumably less than 50% efficient now.”

      Two points:

      1. Your gas will have lost some of its original efficiency, but is highly unlikely to have dropped from ~70% to 50%, even if never ‘maintained’. It may have dropped 5%-10%.

      2. ” ….. when new 30 years ago….” Do NOT expect a modern boiler or heat pump to last that long. When the ‘carbon cost’ of two or three replacements during a 3-decade term are taken into account, your old boiler will be seen as the ‘most efficient’ system.

      • Joe Public permalink
        December 20, 2015 7:16 pm

        Ooops – ‘1. Your gas boiler ……’

      • A C Osborn permalink
        December 21, 2015 4:40 pm

        Totally agree, the cost of a new Condensing boiler (a very good one) barely pays for itself before needing replacement.
        Get the wrong one, after 23 sterling years service by a non condensing one as I did, relying on a local installer that I trusted, silly me.
        It lasted 3 years (better than others experenced) before needing a new Diverter Valve, all savings wiped out at a stroke, it then needed another one after 18 months and then the CPU failed after a further 6 months.
        I have now bought a more expensive, supposedly more reliable one, but I am keeping my fingers crossed as I no longer believe the hype.
        It was Government backed hyperbole to give a massive kick start to Condensing Boilers, whose very design makes them less reliable.

        On top of all that I hardly noticed much difference in performance, except you can bath as often as you like without having to wait for the “Tank” to refill.

  4. John F. Hultquist permalink
    December 20, 2015 6:19 pm

    Our house (2200 feet elevation, 100% electric, built with ducts, AC and Heater) is at 47° North Latitude. During the past 25 years the low temperature was -17° F. (-27° C). Without the built-in ducts, other issues have to be considered. Our State Department of Ecology, because of air quality problems, encourages replacing “carbon producing” stoves with heat pumps.
    About 10 years ago the heating unit went out. We replaced with an air-source heat-pump/AC. Had we had the extra money the ground source would have been possible because we have the outside space for trenches and pipes. The advantage is because when the air becomes too cold the heater switches to “resistance coils” or electric resistance heat. Where winters do not get very cold the resistance heating isn’t necessary so initial costs and operational expense for electricity will be less.
    Here is a good summary:
    An image from a UK site of the trenches for ground source:

    The filters require cleaning that the homeowner can do. A yearly inspection, cleaning, and adding refrigerant (if needed) is a good idea. The units have a SEER rating [Seasonal Energy Efficiency Ratio] that measures air conditioning and heat pump cooling efficiency.

    Trane ® and Lennox ® are two of the major suppliers in the USA. The web sites are sources of information.

    • Kelvin Vaughan permalink
      December 20, 2015 6:43 pm

      There was a program on TV recently where an old couple had changed to a heat pump system thinking they were going to save money. They got a shock when they received their electric bill. Most of the time the system had be running on the electrical back up heating at standard rate electricity costs.

  5. Dave Ward permalink
    December 20, 2015 7:32 pm

    All these supposed savings ignore the payback time. I still have an older non-condensing boiler – it’s some 20 years old, but delightfully rugged & simple (and parts are still available). Ask any heating engineer or trade supplier how long a modern condensing boiler is likely to last, and you will be told typically 7-8 years before expensive repairs are needed. Now factor that against the initial cost of installation (and as Joe Public explained) the larger radiators which are often needed to get the same level of heat. The result is your “predicted” savings will be neatly cancelled out…

    Now go an order of magnitude further with a heat pump – either air or ground – they both use the same basic technology. Compressors and motor driven fans wear out, refrigerant can leak, and just imagine the problems you would have if a ground circulating coil developed a leak! It’s already accepted that air source won’t be much use during extended cold spells, and even ground source can lose efficiency if required for long periods of cold weather. With respect to John F. Hultquist, the trench area in the picture he posted would have three or four houses on it in the UK!

    I have a further observation – If the majority of UK homes and businesses eventually convert to heat pumps, (and they are mostly air source) what effect will all the cold air they put into the environment have? I can foresee a “Reverse UHI” effect in winter, where built up areas will be colder than open countryside…

    • John F. Hultquist permalink
      December 20, 2015 11:34 pm

      The photo was from a UK site (not mine), but I did not see info about it.
      The coils seem to be black plastic — not what I thought. Gophers can damage underground utility cables, TV cables, and irrigation pipe.
      Lots to worry about.

  6. December 20, 2015 8:03 pm

    Ed Milliband (remember him?) is now pushing for a ZERO carbon target, so our grandchildren would only be able to use their expensive and ineffective heat pumps when the wind blows. He talks about owing it to his children, the war on this madness must continue.

    • Keith Willshaw permalink
      December 20, 2015 8:27 pm

      Is he going to lead the way by committing suicide ?

      Human beings do emit CO2 after all.

  7. Keith Willshaw permalink
    December 20, 2015 8:26 pm

    There is no reduction in CO2 emissions from this, in fact there is a considerable increase. The simple fact is that even at best wind delivers less than 15% and frequently less than 5% of the power we use. This means that most electricity comes from gas. The best Combined Cycle Gas Turbines are less thermally efficient than even an old non condensing boiler especially when you factor in transmission losses.

  8. December 20, 2015 11:13 pm

    It’s kinda neat the way these heat pumps can give you 3KW of heat for every 1KW of electricity – but since UK electricity is currently 3x as expensive as gas, it cancels out any cost benefit apart from the RHI subsidy. Thanks to shale I don’t see gas becoming more expensive relative to electricity any time soon (unless the government go nuts with carbon taxes). So I think I’ll stick with my GCH thanks. But I guess a future government may legislate for all new houses have to have ASHP rather than GCH – assuming the whole global warming scam continues that long.

  9. Franklin T. permalink
    December 21, 2015 2:53 am

    Heat Pumps do a good/great job removing heat during hot weather, however their heating ability seems only fair at best. I have one and during near 10 degrees F weather or colder you have to be dressed fairly heavy to stay warm as the “feel” of their heat pales in comparison to the “feel” of gas heat or other sources in general. Thanks to my insurance restrictions I am stuck with a heat pump as my only heat source for now.

  10. December 21, 2015 4:26 am

    Rule of thumb is that a sum of 10,000 invested for 20 years will return an annuity of

    1000 (1/10) if the rate of return is 8%

    850 (1/12) if the rate of return drops to 6%

    700 (1/14) if the rate of return drops to 4%.

    (These fractions are within 5% of the actual figures.)

    The assumption is that the fuel savings is equivalent to an annuity. Alternatively, investing in financial asset an amount equal to the cost of a heat pump would return an annual amount enough to compensate for the extra fuel cost required to run less fuel-efficient technology.

    Assuming the heat pump can last for 20 years without major overhaul and the routine maintenance is negligible, savings of 700 to 1000 per year are needed to justify the investment of 10,000.

    For this to apply, alternative investments of similar risk would return between 4% and 8%.

    Since frakking will probably cause the price of gas to fall, this does not seem to be a secure investment for gas customers. (Fuel pricing would be a risk factor.)

    Moreover, maintenance costs for the heat pump would probably be higher than estimated here and a major overhaul of the heat pump might be needed within the 20-year life of the heat pump.

    A positive factor would be that existing equipment will almost certainly have to be replaced at some point. The cost of replacement equipment would partly offset the capital cost of the heat pump.

    Conclusion: Investment in a heat pump is not justified except for customers who must use LPG.

    Some customers using old storage heaters should check further about switching to gas.

  11. john in cheshire permalink
    December 21, 2015 12:21 pm

    There are several companies that I’m aware of that epitomise the poor business case for new energy technology. Two examples are Ceramic Fuel Cells and Ceres Power – good in theory but in practice neither has managed to their products into a profitable business despite lots of money and determined effort over many years.

  12. S Allnutt permalink
    December 21, 2015 3:12 pm

    Air sourced neat pumps lack efficiency when you need them most, when the outside temperature is very low. I have an inverter a/c which will not work at below -10C (14F).

  13. T. Bone permalink
    February 17, 2016 5:36 pm

    To answer David ward: Air source heat pumps do not ‘remove heat’ from the atmosphere they add to it. The heat that is extracted from the air is supplemented by that added by the work done of the compressor ( as well as heat from any fans). The heat that is then transferred to the building escapes back to atmosphere via losses through he walls, windows, roofs and floors. Simple physics.

  14. BarryM permalink
    March 19, 2016 12:36 am

    Reading the comments below, do any relate to first hand experience of a HeatPump System?

    As a Heating Engineer, many factors have to be considered on a retrofit. In the case of a full refurbishment with correctly designed UFH, some inverter Ashp models will defeat the cost of a Natural Gas Condensng Boiler when combined with OffPeak Electricity and indeed some of Solar PV deals.

    HeatPumps are evolving as the U-Values for new buildings continue to fall. The market share of HeatPumps for Domestic Heating will continue to increase regardless.

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