Insulate or DIE! They cry.

To insulate your home seems like a perfectly rational plan. The more you insulate your home, the less energy you will use keeping it warm over winter.

But there is the question of cost effectiveness to consider. If the outlay on insulation was cost effective, we’d all be doing it. But Insult Britain probably don’t care how cost effective insulation is: they want the government to pay for it. (Naturally, that means that we will all pay for it, but that the bill will be socialised; a bit like those “free” smart meters.) Would it be a cost-effective use of taxpayers’ money?

Thinking along these lines, I wondered exactly how much we ordinary folk could save by insulating our homes. Just what was the potential saving? Half the bill? A quarter? To listen to Insulate Britain’s spokespeople you would assume that the potential must be very high indeed, that insulation was a miracle cure for poverty. Is it? It seemed obvious to me that insulation must follow a law of diminishing returns – cheap and effective things are easily done, but addtional measures become more expensive and less effective. And that’s without considering the attendant perils of damp.

It ought to be possible, I thought, to work out what proportion of our energy bills could be gripped by extra insulation, and in so doing work out what the potential savings might be.

For a dual-fuel household, bills have a number of parts. First is the unavoidable standing charge on both gas and electricity. Then, assuming that the household has gas central heating, the remaining energy is divided thus: electricity; gas for hot water and cooking; and gas for space heating. Only the latter subset can be reduced by insulation. But what proportion of a bill is it?

Gas vs Leccy

A typical household with gas central heating obtains a lot more energy from gas than from electricity. Ofgem says this is 12000 kWh gas and 3100 kWh electricity. So it’s roughly 4:1.*

A very old (2014) DECC statistical release showed total domestic use in the UK as 43,794 thousand tonnes of oil equivalent (a horrible metric, but still). Of that, 28,728 was used for space heating: therefore, roughly 2/3 of the energy used was for heating.

Of course, gas is (still) cheaper than electricity, so if you used gas for heating you would have spent less than if you used electricity (the leverage available to heat pumps notwithstanding; in any case there weren’t many of these back in 2014).

According to DECC back when, ¾ of gas use was for space heating. Now, this is a good moment to insert a caveat: this figure does not relate to a typical home, but to the average home. There are differences in the way households are set up. Even those with gas central heating might have electric cookers. Some folk are still using gas fires. And so on. But handwaving madly, that means the pseudo-typical home is using 9000 kWh of gas for heating, or at least that’s what I’m saying it’s using. (Edit: this doesn’t matter really here because the data on energy savings appear to relate to the entirety of the gas usage, not just the heating element. The latter figure would be harder to obtain.)

All this means that as a first pass estimate, insulation can work on ¾ of gas use.

Now, what sort of savings might we expect from our new insulation? My assumption is that there is no point at all talking about loft insulation: does anybody know anybody who doesn’t already have it? And that applies to social housing and rental as well as owner-occupier places. As I said: the easy stuff has been done. But say what you like about BEIS (go on, say it), they do produce a lot of data, and they make it available, if you search diligently enough. BEIS have a scheme called NEED, describing in detail how their policies have increased poverty in the UK. (Actually it stands for National Energy Efficiency Data Framework, and uses empirical data to measure the effect of energy saving measures; data here.)

Here we can find the effect of fitting loft insulation: a reduction in gas usage of 2.6% (mean; median is 3.7%). Other measures are better, one suspects because most of us don’t already have them. That hideous solid wall insulation glued to your house will save an average of 17% of your gas usage.

But BEIS go one better: they produce more detailed statistics showing how the benefits of energy saving measures vary by the properties of the home. Thus fitting loft insulation to a home with an EPC (energy performance certificate) rating of A will only save 1.4% on your gas usage (but, one can’t help wondering: how does a house achieve an “A” rating without loft insulation?)

The professional eye might notice some oddities about the table. Like the way that although the overall mean saving of gas is shown as 2.6%, the lower quartile is -12.9%. In other words, the data is extremely messy and the error bars are rather wide. Other tables (not shown here) show that detached houses achieve a better saving from adding loft insulation than mid-terraced houses (5% vs 1.4% mean savings) and that for some odd reason private renters increase their gas use after fitting loft insulation (-0.4% percentage saving on average).

But the overall averages look like useful guides. If we add the energy efficiency measures up, we get 3.8% savings from fitting our condensing boiler, 8.1% for cavity wall insulation, 2.6% for loft insulation and 17.0% for solid wall insulation: that’s 31.5% in savings. Not bad? Well, maybe. Except people tend to already have most of those things, the exception being solid wall insulation, which will save you that 17.0%. [Speaking personally for a minute: our house has cavity wall insulation in the bits of wall that actually have a cavity (a 1980s extension); we have loft insulation and a condensing boiler. So for me personally the potential is 17%, except it isn’t, it’s 14.4% because our house is a mid terrace (so says another of the many BEIS tables).]

We are now beginning to get a sense of what is possible: somewhere about 17.0% saving in gas usage for a “typical” home, but varying up to about 31.5% if you have no insulation in the loft, empty cavity walls, and an old back boiler.

The “typical” situation therefore gives a saving of 17% on 12000 kWh of gas (in drafting this a minute ago I was only applying this to the “space heating” part, but the figure relates to all gas usage), and the price cap “default tariff” is £0.15/kWh. That’s 17% of {12,000 kWh x £0.15/kWh} £2,040, or £306.00. Not a trivial sum if someone were to just trim it off your bill or put it in your hand, but of course that isn’t what we’re talking about here. We’re talking about making an investment now to save that potential £306.00 each year on your gas bill. What sort of investment? I must confess I have no idea how much solid wall insulation costs. I’ll ask Mr. DuckDuck. Looks like £14,000:

So the payback time is… £14,000 / £306.00/yr = 46 years

Of course, this may not matter to Insult Britain, who are dealing with Other People’s Money. But if one is dealing with One’s Own Money, it is not a very good deal at all. And most people would prefer 14 grand in their hand rather than £306.00 a year for 46 years. In reality most people would borrow the sum, and the interest would likely exceed the annual saving, even in these times of stricture. Having spent your 14 thou, your annual bill from 1st October, assuming no further changes, would be £3376.29 instead of the £3682.29 mandated by the price cap – a saving of 8%.

Now, the more expensive energy gets, the better the energy savings options seem. Like the way that pair of patent yellow leather shoes eventually starts to look like a roast turkey if you’re hungry enough.^ But if rationality ever returns to UK politics, we can look forward to a rapid drop off in energy costs. Can we? Please say we can.

Roll on Global Warming

Ovo put out an energy guide last year, which had an interesting comparison between European countries’ energy usage:


The moral seems to be: Don’t winter in Denmark, or do winter in Portugal. Note: the Ovo figure for heating is the same as the Ofgem figure for all gas use, including hot water and cooking. There is no footnote to say where the number comes from. But also on the global warming theme, elsewhere in that DECC document there is this statement:

From 2012 to 2013, space heating increased by 0.4 per cent. This coincided with a 0.6 degree Celsius decrease in average heating season temperature.

Things are looking up guys! On this basis, a mild winter (thanks to global warming) might even save us the cost of a pint.


If your house was perfectly insulated, your energy bill next year would be £2332, not £3682. The same applies if you switch off your boiler for the winter. In reality you’re likely to cut 8% from the bill with a £14,000 outlay.


*Ofgem reduced the electricity “typical domestic consumption value” to 2900 kWh a couple of years ago. The other value is still widely published I think, including at Ofgem. (They still use this to calculate the default tariff.)

^But don’t bury me in mine. See Nick Cave, “Higgs Boson Blues.” Just incinerate or compost me. Actually I’ve always thought sky burials looked cool. But I guess 21st century humans are too toxic to feed to the birds.

That DECC data.

Featured image

A banner used by Insult Britain in the High Court – Daily Mail story here


  1. Jit, once again, thank you.

    I’m not against insulation, done sensibly and properly – for instance, we (as do most people, you speculate, and I’m inclined to agree) have loft insulation, and for good measure we have just updated our double glazing. So the amount of insulation options left to us are declining. And the same is probably true for many households up and down the country. It’s difficult to avoid your conclusion that potential savings (even in these times of unusually high energy costs) are limited, and certainly don’t offer a realistic payback timescale.

    Then you’re right to mention the potential for increasing damp. It can be a big problem – see

    In short, those touting insulation as the simple panacea to solve all our heating bill problems are, frankly, detached from reality. Almost childishly so. Yes, there are some savings to be made. But no, they’re not substantial. And, along the way, many insulation schemes do more harm than good.

    Liked by 2 people

  2. “But the overall averages look like useful guides. If we add the energy efficiency measures up, we get 3.8% savings from fitting our condensing boiler, 8.1% for cavity wall insulation, 2.6% for loft insulation and 17.0% for solid wall insulation: that’s 31.5% in savings.”

    The cumulative percentage savings from multiple efficiency actions are a diminishing return.

    0.962 x 0.919 x 0.974 x 0.83 = 0.7147 >> 28.53% cumulative savings

    Liked by 2 people

  3. “But don’t bury me in mine. See Nick Cave, “Higgs Boson Blues.” Just incinerate or compost me. Actually I’ve always thought sky burials looked cool. But I guess 21st century humans are too toxic to feed to the birds.”

    Sorry, I can’t resist this …. it doesn’t relate to insulation, but in the context of your comment is perhaps a superlative example of useful recycling:

    “Redditch Crematorium begins to heat town pool

    Abbey Stadium leisure centre is finally using waste heat diverted from Redditch Crematorium a….
    Redditch Borough Council expects the scheme to reduce the centre’s gas bill by aver 40%, equating to a saving of about £15,000 a year……”

    1.That £ savings will multiple times greater with today’s energy prices!

    2. Today’s energy prices are likely to increase Excess Winter Mortality, so the pool’s energy savings will be even greater.


  4. Joe, do the locals call it the Dead Pool?

    *insert tumbleweeds*

    Regarding the diminishing returns: I thought about that when typing out that sentence, but decided to leave it as the “best possible” outcome. The BEIS data does show the results of adding two energy saving measures at once, but as before the data is messy. (And they don’t show data for 3 or all 4 measures.)

    Liked by 1 person

  5. Dunno about the ‘Dead pool’, but the cost of cremations will skyrocket, and that alone will likely give the elderly who most tend to plan them, premature heart failure. 😉


  6. Radiative test for heat loss from my house. My car is parked approx 2.0m from our house, during times of frost 0 to -5c the house side only requires a light wipe to remove the ice, the far side a bit of scraping. For temps below -5c requires spray and elbow grease all round. At about -10c the near side door still pulls open, the far side getting sticky. Down to -20c both doors stuck , go back inside and wait for the thaw !!!


  7. “Controlled opposition”
    Imagine a George Orwell book where SuperState creates a youth opposition movement, which has exactly the same aims as SuperState
    and then names them The Rebellion
    and somehow they are magically able to get right to the central government chamber and do a protest all the media cover
    ..And like all their other protests they magically walk free from the courts

    PJW has a new vid about XR being allowed into Parliament
    whereas if anti-lockdown protesters had tried the same stunt …

    Liked by 1 person

  8. Sitting in my house (25yr old, gas fired radiators) – all rooms have 3 air vents, 1 in the wall & 2 in windows.
    they have sliders to open/close, but even closed you can feel the draught coming in.

    my 1st house had no vents & a gas fire, in the winter the windows were running with condensation.


  9. The reported savings for a condensing boiler seem rather low.
    My old boiler was supposed to be 76% efficient when new, according to the manual: probably less than 70% today. Condensing boilers achieve something like 95%, aiui.
    So changing my boiler should reduce my gas consumption by close to 25%.
    The boiler needs changing anyway as it’s become unreliable and some parts are no longer available. At least it should cut my running costs significantly.


  10. Mike, those figures are based on measured gas use before and after the boiler was fitted. However, it does not say what the boiler replaced – presumably mostly combi boilers? The efficiency achieved by your new boiler might not be as high as promised, because it depends to some extent on how good the radiators are and on the boiler settings.

    As an example of the latter: we recently replaced our boiler. The new boiler has a default “pre-heat” setting as standard. This keeps a small amount of water hot within the boiler, so it fires up even in the middle of the night (something I hadn’t realised until recently). It took quite a bit of combing the internet to find out how to turn it off. There were no relevant instructions in the (online) manual.

    It seems that new boilers also have to come with an additional “green” feature. Ours came with a wifi thermostat and can only be controlled by an app.


  11. Jit; thanks for those comments.
    Wrt efficiency the boiler man was here earlier and said much the same – the figures quoted are very much based on factory testing. But then so are the ones for my old unit so, hopefully, I should some a noticeable improvement.


  12. Meanwhile, the insulaters are still at it:

    “UK must insulate homes or face a worse energy crisis in 2023, say experts
    Cutting heat loss from houses will be more effective in the long term than subsidising bills, according to analysis”

    Britain will be plunged into an even worse energy crisis in a year’s time without an immediate plan to improve leaky homes and dramatically reduce demand for gas, ministers have been warned.

    The UK ranks among the worst in Europe for the energy efficiency of its homes, according to new research outlining an urgent need to reduce the amount of heat being wasted….

    …Research from the Institute for Government (IfG) found the UK scored worse than countries right across Europe with a range of climates in terms of the energy efficiency of its homes. Citing analysis of a 2020 study, it found that a UK home with an indoor temperature of 20C and an outside temperature of 0C lost on average 3C after five hours – up to three times as much as homes in European countries such as Germany.

    The cited research can be found here:

    The government should do more to address the UK’s energy efficiency problems – or risk finding itself in an even more difficult position next year over rising energy bills.

    The report finds that the UK’s homes and buildings are among the least efficient in Europe, which is making the energy crisis especially painful for UK households and businesses

    The Johnson government and now seemingly the Truss government have so far ignored energy efficiency in their responses, but the new IfG paper says the case for action is even stronger now that the government will be taking such large energy costs directly on to its balance sheet.

    But with the UK paying the price for a decade of policy failure on energy policy, with ministers giving the issue insufficient attention, the report sets out how the government can learn from successes abroad and failures at home, and develop a stable, long-term approach that builds confidence among consumers.


  13. Another push on this subject by the Guardian:

    “Energy-saving measures could boost UK economy by £7bn a year, study says
    Exclusive: Green home upgrades could also create 140,000 new jobs by 2030, analysis by Cambridge Econometric finds”

    Insulating homes in Britain and installing heat pumps could benefit the economy by £7bn a year and create 140,000 new jobs by 2030, research has found.

    But the uptake of these energy-saving measures depends heavily on government policy, according to analysis by Cambridge Econometrics, commissioned by Greenpeace….

    I’m afraid those last three words ruin any credibility the research might have, so far as I am concerned.


  14. “Not too late to insulate homes this winter, says Lord Deben
    Climate Change Committee chair says measures needed to cut energy bills will also help reach net zero”

    …Deben said soaring energy bills were at the heart of the UK’s economic crisis. “The problem is, how do you lower the cost of energy? There are two ways to do it: one is you have more renewable energy, because that’s the cheapest form of energy, and the second way is that you enable people to use less energy by having energy efficiency. They are quite clear and simple and they can both be done,” he said.

    The private sector could also be involved in financing insulation schemes, he suggested. “There is a wonderful opportunity, and there is a great deal of private-sector money in there, if the government creates a scheme.”

    Deben called for ministers to do more to help people make low-carbon choices, saying people approaching plumbers or heating engineers were often sold boilers instead of heat pumps. “I’m very keen on proper government policy so that somebody can ring up and say: ‘Look, I’ve got a three-bedroom house, I want to do the right thing. Instead of buying a new gas boiler, where do I go to get the information?’ And there should be very direct help.”

    New homes are still being built with gas boilers, without renewable energy and to low standards, and will have to be expensively retrofitted in the future to meet the 2050 net zero target. Deben contrasted this with the government’s success in stimulating the car industry to produce electric vehicles by setting a deadline of 2030 for the last sales of new petrol or diesel cars…

    Utterly delusional.


  15. A very interesting interview on BBC Radio 4’s PM programme this evening, with an expert in home insulation (or some such) from Oxford University. When she told Evan Davis that there are around 27 million homes in the UK, and insulation sufficient to make meaningful energy savings would cost around £10K each or £270Bn in total, he nearly fell off his chair.

    I don’t think most people (even including journalists and media types who one might hope would be reasonably well-informed) have a clue how much all this net zero stuff is costing.


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