CO2 & £££ savings of Heat Pumps
This is my site Written by admin on March 30, 2009 – 12:50 pm


The concern about the heat pump is the running costs. Even though the efficiency is 1 to 4 (1kWh in gives 4kWh out), the economics & CO2 savings are somewhat different.

My last bill including VAT

  • 1 unit of electricity = 14.58p
  • 1 unity of Gas = 5.17p (see note about split costs below)
  • No. kWh of Gas used = 2389
  • Gas bill was £124.40

As a rough approximation, if we needed the same number of kWh (i.e. 2389) and using a Coefficient of Performance (COP) of 1 to 4 for the heat pump, then I would only need 597.91 kWh of electricity to generate 2389 kWh.

But, hold on guys, lets work out the electricity costs :-

  • 597.91 kWh will cost 597.91*14.58 = £87.08
  • My Gas bill was £124.40
  • Saving is £36.32
  • Difference = 29.4% saving on £££

Hmm, and what is the CO2 savings (units from EST) ?

  • 1 unit of gas = 0.206 KgCO2
  • 1 unity of electricity= 0.537 KgCO2
  • CO2 generated from GAS = 2389*0.206 = 492.1 KgCO2
  • CO2 generated from ELECTRICITY = 597.91*0.537 = 320.7 KgCO2
  • Saving is 171KgCO2
  • Difference = 34.8% saving on CO2


This is only looking at less than 1 quarter’s bills (24th Dec 08 to 2nd Feb). Since I have split unit prices on my Gas (i.e. the first 1145 units costs 7.465p and the rest at 2.577p), then the more gas I use in a quarter, the lower the unit price as compared to the calculation above. This would imply that my real unit cost of 14.58p per unit will drop and therefore the economics will work out to be less favourable.

The other point was that I was hoping to be able to offset my electricity usage with PV, but since the amount I would get would be less than what I am currently using, this is a non-starter. So getting to zero via this route meets a hard stop if you have to use electricity. You could offset your CO2 from electricity usage but the savings aren’t all that favourable.

I would probably have to have 2 bore holes drilled (2 x 60m) and at £37/m, thats £4440 capital costs.

So my thinking is to sink my capital into significant insulation (hence reducing the need for energy) and this would also keep the inside of the house cool in summer. If we’re going to have summers like Morocco or Southern Spain, then this will help.

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5 Responses »

  1. Hi Rob, long time since we initially met (at Southampton’s green fair, 2yrs ago), but nevertheless I hope you remember me – but maybe not.
    Sorry to appear to antagonise here, but I cannot resist what I think can be very misleading information; and I’m not suggesting that you are deliberately doing so, but more because it’s been overlooked perhaps – certainly it’s hardly discussed in the wider media either:

    If we’re talking about actual impact on the planet, as well as from an economic standpoint, then may I bring to your attention to this other major consideration: that of the inefficient power generation and distribution network. This works out to be about a 2/3rds loss when all is factored in. Hence 1kW at the point of delivery to the home represents 3kW of energy used; and this is generated, in the main, by coal-fired power stations which also means considerable greenhouse gas emissions.

    So, even if one can debate the merits of one power source over another, it needs to include the impact in totality, not just at the point of use; much as so-called ‘zero’ emission electric cars are anything but! The car itself, in use might indeed be; but this is totally overlooking the fact that the electricity needed to charge the vehicle in the first place, comes from a CO2-producing source. So using the vehicle is certainly causing CO2 emissions; and don’t forget that it’s a factor of 3 times what the consumer might measure, based on what the charge wattage is, given the 2/3rds of losses I’m highlighted….. and of course this also completely discounts the embodied energy of the vehicle production in the first place, which is pretty huge!

    I realise it’s difficult to include everything, and accurately, when giving ‘cost’ comparisons; but these figures are hardly ‘minimal’, and whether we like it or not, ARE very much a part of the equation.

    So, although the arguments for and against different technologies when counting the immediate cost to the consumer, as it hits their pocket directly, from the point of view of ’emissions’, with known figures such as those I’ve given and the significant affect they have on the figures, it’d be more accurate and all-encompassing to include these when comparing greenhouse emissions.

    I hope you’d agree with what I’ve pointed out and take this into account, and factor in to the figures you publish for public consumption. The wider public can be forgiven for not knowing what lays deeper beneath the plethora of figures to do with the environment, as it takes a fair bit of time to get to the bottom of things, which most folk just don’t have the time for. So being a died-in-the-wool eco-warrior, this is what I investigate and spend a lot of time doing, precisely because I know that the general media, and indeed industry, don’t convey the whole story. It’s therefore not a balanced playing field.

    All the best Rob :)

  2. Thanks Ian, for this. Good to hear from you.

    I stand by my original thinking (which was stated to be approximate) providing the data from the Energy Saving Trust is correct. I have reasonably assumed that the kg figure takes into account a range of energy sources – coal, combined cycle gas fired power stations (42-45% efficiency), nuclear, windpower etc… At the time of producing the entry, there were limited tools available to help may the comparision, although this is now starting to change. (eg

    The CO2 kg per unit of energy seems to be a reasonable way of calculating the basis for a carbon comparison. I accept there are plethora of other factors to take into consideration such as embedded energy, the end to end delivery of energy into the home, real lifetime costs of energy production etc… Most of which are not within my power to significantly change. And I accept my calculations may not be 100% correct, but we need a general rule of thumb to achieve a reasonable conclusion. The 80/20 rule is good enough for me and I suggest for most people. To get into a detailed debate politely put, simply turns people off. Another critical factor towards making a decision will be cost, and cost savings. I donot think my calculations were out by a significant factor.

    From what you say, there is an “energy efficiency” consideration. I think this may well have strengthend the approximate analysis, and conclusion not to go for a ground source heat pump.

    What became apparent was the obvious, and in hindsight may not have needed these approximate calculations. It was not to have a house that was energy inefficient in the first place. i.e. whilst there may have been some savings in CO2 and £££ due to the technology, it didn’t seem to be solving the underlying problem. The house was inefficient both in the use of heating and electricity.

    So did I reach the wrong conclusion? I don’t think so.

  3. I found this very useful, thanks for sharing.

  4. Quite some time has elapsed, since I contributed above, Rob, so I apologise for not having come back to your earlier. I have been snowed under doing some refurbishment work at home here, which has been pretty slow progress (ever the perfectionist, but it does rather impede things!).

    I have of course read your response to my initial comments, and as you say, things beyond your control, as well as figures given by third parties cannot be duly validated, so giving ‘exact’ calculations/environmental impact assessment is difficult at the best of times. However, this wasn’t the main thrust of what I was trying to convey.

    There has to be a certain level of ‘trust’ with any given figures, but in part, this actually can help less than reputable companies mask, or otherwise paste over inconvenient ‘cracks’. Greenwash abounds, which is a large part of what I was alluding to, even from some otherwise ‘independent’ sources, as often these may have in-built bias, much as ‘independent’ financial advisers being tempted by those institutions that pay the highest commissions. So, while this might sound defeatist, in actual fact I’m only saying that ANY published figures, no matter the source, are to taken with more than a modicum of salt.

    Furthermore, the other thought behind my comments and stance, is that the starting point of any environmental debate should ideally be the lowest common denominator: the least processed or complex. Much as with food, the simplest, unadulterated variety is often the healthiest. So essentially where I’m coming from is that of low-technology answers wherever possible, IF it’s appropriate; but this should be the starting point, as opposed to going high-tech at the outset, which the capitalist system invariably supports.

    So, Rob, there is no definite right or wrong here, as it’s inherently difficult to ascertain; I’m only bring to the attention of other readers, the fact that behind all the ‘figures’ lay a very shaky base, for one reason or another. Too many assumptions at the starting blocks, and that any error made in the early stages gets magnified as the figures pile up.

    I would like to extend this, by way of example, to wood burners: Ask the average man on the street, and indeed even many environmentalists even, if a woodburner is more environmentally friendly than gas central heating? I would say, and fairly confidently, that the vast majority of people would say ‘woodburners’. However, contrary to contemorary popular belief, this may well be untrue if looking at the bigger picture.

    A woodburner is sold on its merit of being supposedly ‘carbon neutral’ (the amount of CO2 released when the wood is burned, being equal to that which it absorbed, as a tree, during its lifetime) which gas isn’t. So, on the face of it, woodburners appear greener. But what many don’t know, nor take into account, is the fact that for the same heat generated, wood burning produces twice as much CO2 as gas does. Furthermore very little study has been done to quantify how much of the CO2 absorbed into the wood is then created/wasted for all the stages of its reclamation: the machinery, all fossil fuel powered, to harvest it, process it (worse, chip it or kiln dry it!), distribute it and then store it before being sold, whereby it’s then again shifted around using fossil fuels, often overseas, before eventually reaching the consumer.

    There is a school of thought that says we’d actually be better off consuming the gas (half the CO2 emitted on combustion, processing, extraction and distribution [and leaks] aside) and saving what would have been felled trees for fuel, for 50% less felled trees for example, which can be turned into furniture, which lasts well, saves using more harmful alternative materials, and leaves more trees standing. Of course this also means that the trees ‘saved’, so still standing, also continue to absorb CO2, which they’d cease to do if felled. It’s quite an in-depth study, and as I have said, when it comes to the figures, it’s so very difficult to quantify or be specific about, so we need to tread carefully. However, I’m just backing up, by way of example, what I’m driving at, which is that many figures are to be taken with a large pinch of salt – even those stated by me – as there are so many OTHER aspects and considerations to be taken into account. If we allows ourselves to get too bogged down with the detail, we run the serious risk of overlooking far more important factors affecting things.

    If we all use a bit of common sense by simply using and consuming far less than we currently do, as well as the ‘make do and mend’ mentality, and try to support as local a set of people as one reasonably can, then we’re on the right path. All these environmental measures and savings can be lost in one fell swoop, if we then decide without much thought or consideration, to have an overseas holiday, which entails flying. ALL of one’s effort to reduce their carbon footprint have just been blown, and some, in one decision. I’m not saying we should not fly! Only that we need to be mindful of it and reduce our lifestyle impact. If we don’t, we WILL ruin it for future generations. How does common sense explain and deal with our over-consumptive habits? We are sadly wedded to what we see as solutions that invariably include yet more ‘stuff’. We are led to believe we need it, when we don’t. That carrot is forever out of reach; and this short termism is never fulfilling, nor feeds our real soul. We’re not biologically designed to eat the diet we have now, the calories we intake, and the very little physical movement we generally exert. Hence many people are overweight, unhealthy and certainly not truly happy! We’ve lost much for our modern lifestyles, and with it the millions of years that nature has spent depositing and creating all the energy our planet had accumulated, but which we are now using up far faster than we are replacing it.

    Perhaps you may consider that I have digressed rather. I’d forgive you for thinking that; but again, I’m talking the bigger picture here. It’s ALL linked. We just need to join the dots in our heads to see it.

    Apologies for having posted a rather wordy contribution; but I sincerely hope it’s for the greater good, in that it plants the little thought ‘seeds’ in your readers minds – if they weren’t already there. Life it never easy, but it can be made simpler.

    All the best, Rob.

  5. Oops, I forgot to mention, Rob, that I have a woodburner myself, if it’s thought that I was bashing them. I’m not, but only demonstrating that I’m open to other points of view with regards to environmental impact CO2 wise. Besides, I cut my own wood, being a woodsman/environmentalist, from a local source, so minimal carbon consumed in harvesting the wood, and especially when I transport it back to my home where I split it all by hand :) Whether this makes any difference to the debate, is neither here nor there; I only wanted to point out a fact.


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