I saw a big uptick in discussions about heat pumps recently, in response to gov plans. An engineer's letter to the Guardian really caught my eye. The sections in *s are particularly important.

"Your correspondents are too gloomy about heat pumps for houses and flats (Letters, 20 October). Heat pumps may be unusual in Britain, but they are a major industry and very widespread in Europe and elsewhere. They are used in Canada, where outside temperatures drop very low. Individual units may not be suitable for high-rise blocks – although they might be installed on balconies. But high-rise buildings make up a small fraction of the housing stock, and blocks can have communal heating and cooling with large centralised heat pumps.

Older heat pumps were noisy, but new makes are on the market that are much quieter. *It is not true, except in the worst cases, that installing heat pumps requires dwellings to be insulated first. The great majority of houses and flats in the UK are already reasonably insulated,* and heat pumps can be run for longer and at lower temperatures than gas boilers. *Better insulation of existing gas-heated houses and flats will by itself only produce modest cuts in carbon emissions*. To meet climate goals, we have to stop using gas.

And, by the way, hydrogen as a domestic fuel – being pressed hard by the gas companies – is a distraction. It has to be made either from natural gas, which produces CO2 and can also release methane, a much more powerful greenhouse gas. Or it can be made with electricity, by the electrolysis of water. But why would one not in that case supply the electricity direct to houses, for resistance heating, or for powering heat pumps?
Philip Steadman
UCL Energy Institute"

Isnt his statement dubious? Is the average UK house already suitable for heat pumps? Personally, I would be concerned if gov policy was inspired by such a statement. He might be right that UK houses have reasonable insulation but they need far better airtightness to make heat pumps sensible. Roger Brisby has a video where he predicts a lot of people will be misold heat pumps and it seems a reasonable prediction.

My immediate response is to take asharp intake of breath where it says "The great majority of houses and flats in the UK are already reasonably insulated." Given the standard of UK house construction now and historically, I'd question that conclusion, but by "reasonably" it can mean many things.

Before writing the guy off, I looked at his profile at UCL and found the following recent study of energy use intensity in London. Its conclusions actually cross over with recent discussions on the validity of EPCs, but make for some interesting reading if you're that way inclined.

On EPCs:

"When examined in groupings of attached status with age bands, energy use intensities (EUIs; kWh/m2/yr) of houses, based on recorded fuel consumption, do not always track the energy performance predicted by their EPCs.
This is particularly the case for electricity consumption, where there is no correlation between
the Standard Assessment Procedure (SAP) rating of the EPC and electrical EUI. Gas consumption
is only weakly correlated. These levels of correlation indicate that broad-brush policies, based on
EPCs alone, may be limited in their capacity to deliver significant energy conservation, without
further investigation of the issue."

Link to paper:

https://discovery.ucl.ac.uk/id/eprint/10125856/1/79-3447-1-PB.pdf

I can confirm that a heat pump worked very nicely in our previous poorly-insulated drafty old stone house, and I'm pretty optimistic about one working in our next one, and reducing our CO2 by about 90% in one quick go. You just need a bigger one, if there's less insulation.

Interesting to read the public comments below the Guardian articles - most of them from people who are frightened off heat pumps because they are exotic and different, or because their neighbour's cousin heard that that they might only work in new-build houses. Going to take a while to overcome all the misunderstanding and get public on board.

Posted By: Cliff Pope1) sufficient financial inducement
2) believable guarantees that the policy isn't going to change over the next ten years.

Neither of which are likely to happen.

Posted By: Nick ParsonsWhat I don't know is how HPs work on 'partial load', when your 16kW HP is no longer working hard because you've upgraded the insulation.

There's two types of working hard:

(a) long run times at full power avoiding short cycling
(b) long run times at partial power avoiding short cycling

And, for air source HPs, you also want to optimize the number of defrost cycles.

Modern variable speed compressors do well at (b) without loss of COP.

All this talk about heatpumps not working in uninsulated houses is just nonsense. The temperature in the house is purely determined by the heatload at a particular temperature and it doesn't make a difference what the source is. What *is* the problem in the UK is that, due to poor insulation and air leakage, and normal usage mode of heating systems is to have a massively oversized heat source and only run it at certain times of day, thus allowing the house to cool down in between. To feel comfortable, you need massive oversizing to quickly offset the loss in temperature due to crap insulation/air tightness in the firstplace. So fixing these issues allows a heatsource that is more closely matched to the load. Then you can just "set and forget" your thermostat and let the system keep the house warm. I guess as more and more people work from home, keeping a house warm all the time will become more the norm compared to the old "bake/freeze/bake/freeze" cycle that's traditional in the UK

Paul in Montreal

Massively oversizing a gas boiler is so cheap to do, it "makes sense". It papers over the cracks; if your lifestyle involves leaving open doors & windows all year? No worries, the house will still be warm. Newbuild, and the builder forgot to put the insulation in? No worries, the house will still be warm. Even if the boiler and heatpump cost the same, where is the incentive to take the "risk" putting in a correctly sized heatpump at present? The risk that it will expose a build shortcoming that is, as there is a cost penalty oversizing a heatpump. Until there's legislation only greenies will do it due to the significant CO2 reduction, but it doesn't make financial sense at all sadly.

Posted By: djhI remember having to talk our supplier down to a 12 kW boiler in our previous house. But if you have a combi then it does have to be sized to the DHW demand, which is an argument against combis.

Agreed - an installer we spoke to wanted to install an ASHP that was 15-18kW, even though this would have cost more than twice as much for the unit itself. We ignored his advice and went for an 8kW which is what all our neighbours have. So far it's been absolutely fine. It only needs to tick over, probably almost on its lowest setting, to keep us warm.

What size ASHP would people recommend for..

3300 sqft house built in 2007
Currently has a 40kW oil boiler feeding a 300L TS.
TS provides DHW and UFH
TS normally runs at 55C and feeds two high flow rate showers
Suspect house isn't as well insulated as it should be (too much glass on west elevation, upstairs overheats in summer).
UFH is correctly installed but in cold winters need to be run hot by most standards. eg 45C flow rates.

Posted By: djhPersonally I'd suggest the old mantra of insulate, insulate, insulate first. Or rather insulate, airtight, ventilate to be more correct.

Totally agree. We have similar size house part built in around 1750 as far as we can make out .Renovation and extension concentrated on insulation to PH standard, solar gain, thermal mass, air tightness, no cold bridges solar thermal 350 l TSMVHR and just added solar PV. 27 kw LPG boiler UFH (still not switched on) gas bill £297 last year. Expect break even on electric.
Before you spec anything suggest you review what you can do to improve thermal performance of the building otherwise you could be spending more on electricity than oil.

Posted By: WillInAberdeenI can confirm that a heat pump worked very nicely in our previous poorly-insulated drafty old stone house, and I'm pretty optimistic about one working in our next one, and reducing our CO2 by about 90% in one quick go. You just need a bigger one, if there's less insulation.

That's the opposite of what LETI has argued in their LETI Climate Emergency Retrofit Guide
https://www.leti.london/retrofit

"Building fabric improvements are required to reduce heat load so the heat pump can meet demand and operate efficiently with low running costs."

Posted By: Shevek

Posted By: WillInAberdeenI can confirm that a heat pump worked very nicely in our previous poorly-insulated drafty old stone house, and I'm pretty optimistic about one working in our next one, and reducing our CO2 by about 90% in one quick go. You just need a bigger one, if there's less insulation.

That's the opposite of what LETI has argued in their LETI Climate Emergency Retrofit Guide
https://www.leti.london/retrofit

"Building fabric improvements are required to reduce heat load so the heat pump can meet demand and operate efficiently with low running costs."

You're comparing apples and oranges. Will says a suitably large heat pump can operate in a poorly-insulated etc house. LETI's fundamental aim is to get to net-zero and it's first step is to set energy budgets: "how we can retrofit our homes to make them fit for the future and support the UK’s Net Zero targets. We define energy use targets for existing homes". Two completely different goals.

<blockquote><cite>Posted By: djh</cite>Personally I'd suggest the old mantra of insulate, insulate, insulate first. Or rather insulate, airtight, ventilate to be more correct.</blockquote>

Absolutely agree. Wish I had thought of this first instead of spending years catching up!

Posted By: fostertomYes, and this thread is bringing the new news that that conventional wisdom is now outdated, for some latest design heat pumps.

Only if you're willing to ignore important parts of the equation. I think the question and argument about whether heatpumps can work in most homes is a moot point. Basic physics tells us that if you put enough heat into an object to counteract its heat loss, you'll get to an equilibrium. So yes, you can chuck in a huge heatpump if you so wish. However, you then expose yourself not only to significantly larger upfront capital expenditure but volatile long-term operating expenditure which is unpredictable. On the other hand, doing the time honoured thing, as djh suggests:

Posted By: djhPersonally I'd suggest the old mantra of insulate, insulate, insulate first. Or rather insulate, airtight, ventilate to be more correct.

makes far more sense because it's a one off capital expense that then for the foreseable future secures, to a much greater extent, long-term operating expenditure. With energy price inflation over the last few years, together with predicted future inflation due to required decarbonisation investment costs, this is still the most sensible way forwards.

It's almost always easier and cheaper to cut output than it is to increase input into a system.

One other part of this is the false belief that scale will significantly reduce capital costs. Looking at economic history on capital of this nature, it rarely happens in reality, but on another angle the additional total resources required for large scale heatpump implementation would have such high demand on those resources, natural and service based, we're actually likely to see significant increase in upfront costs.

I still can't understand why the debate is still going on.

> makes far more sense because it's a one off capital expense that then for the foreseable future secures, to a much greater extent, long-term operating expenditure.

Proper retrofit is far, far more expensive than the capex on a heat pump. It's the 'best' solution for sure, but the cost of it (and also, less so, the risk of it) is almost definitely why Government aren't advocating it in any serious way.

Posted By: gravelldProper retrofit is far, far more expensive than the capex on a heat pump. It's the 'best' solution for sure, but the cost of it (and also, less so, the risk of it) is almost definitely why Government aren't advocating it in any serious way.

The insulate, insulate, insulate mantra, or even insulate, airtight, ventilate (which is much better already) I just struggle to get on board with.

The cost of a proper retrofit PLUS associated disruption/difficulty is not just high, it's stratospheric. And once you've done that, if you've got a fossil fuel boiler, you need to buy a heat pump (or something) anyway or you'll contine to burn fossil fuels.

I suspect that 'insulate to the extent practical (whatever that is...), then install a heat pump or other system' is what we should aim for...