Electric Heatpumps.

Sorry to lower the intellectual tone but going back to MAPJ's council houses, when you add 100mm of insulation and 100mm of brick to the outside of a house what happens when you get to the roof?

Ethan336: 
A plumber who doesn't like heat pumps, who would've guessed?

Makes absolutely no argument against heat pumps except he thinks it isn't going to be any cleaner than a gas boiler. 

If you have a heat pump with a lowly 2 C.O.P, then you put 1kW in and get 2kW out. The initial 1kW is 25% renewable, 21% nuclear, and the rest is imported or fossil fuels. I put 1kW of gas into my boiler, that is what I get out (minus efficiency losses of course) - which is 100% fossil fuel.

As for the cost side of things, I haven't looked into that and he mentions it - but doesn't address it at all (perhaps he can't because it's cheaper and that invalidates his argument ??) I will definitely be considering getting a heat pump, especially with rising costs of gas.

Running costs of heat pumps are the biggest stumbling block. At the moment, if I decided I wanted to change over I would need to find a heat pump capable of at least 4.8 C.O.P at 80C flow for 0C outside temp to compete with my gas boiler on cost grounds. With the norm for ASHP being around 2.7-3 and a much lower flow temp I don't see that happening soon.

Interestingly, I am currently involved with a major project for a local businessman where we have installed a large ASHP setup to heat his house which he is extending. Despite not being short of money he has been moaning about the ASHP running costs (currently £20-30k/year). Due to large areas of glazing he also wanted a/c to cool about 14 rooms so we've fitted a VRV system which enables it to extract heat from those rooms which need cooling and dump it into the hot water or heating systems. Result, free hot water! 

I feel this would be a better approach for heating houses than trying to get heat pumps to replace gas boilers. Should we go down the road of the USA with new houses having central air systems ducted to each room? Should be better and more efficient than trying to heat up water/floors through UFH and allows for cooling in those sweltering hot summers we get!

Grumpy: 
 

Sorry to lower the intellectual tone but going back to MAPJ's council houses, when you add 100mm of insulation and 100mm of brick to the outside of a house what happens when you get to the roof?

Bang on. A roof extension, though is doable and not necesssarily expensive (you need it for the ends, not for the eaves). For a partial-insulation scenario I had costed, it was between 5% and 10% of the total. (That is in Germany, though.)

I think that if the eaves don't extend beyond the added cladding (like my Victorian terrace) you get a sloped surface edge. And the way building trades work, it's probably “guaranteed for 10 years, isn't that good!”.

After 20 years it probably dumps a load of rainwater into the wall and causes £10K plus damage.

Perhaps I'm too cynical?

OTOH on my 60s bungy the eaves overhang a long way, and external cladding would probably be long term secure.

Gideon: 
 

I think that if the eaves don't extend beyond the added cladding (like my Victorian terrace) you get a sloped surface edge. ……

After 20 years it probably dumps a load of rainwater into the wall and causes £10K plus damage.

Perhaps I'm too cynical?

I don't think you are being too cynical. You are, if anything, being optimistic.

Rooves are things that keep the rainwater out. They are built the way they are because that works (and other stuff doesn't). That construction needs to cover anything vertical. It follows that the eaves need to extend beyond the insulation. If they don't, you need to have the roof extended so that they do. My guess (I haven't had it costed because, like you, I wouldn't need it): add another 10%-20% in cost, because there is a lot more eave than there is gable on your typical inverted-V-roof. And don't forget the new gutters. My guess: extension plus gutters will bring you to 20%, and maybe rather more.

Um, yes. Plus, on the Victorian terrace, external cladding (and its eaves extension) would have to follow round the bay window (which has a tiny flat roof), and account for the elaborate mouldings on the windows (arched tops), doorway, windowsills, and, gratuitously, marking the first floor level. I painted it in 2019, there's barely a half square metre that's flat. And cladding one of a terrace would be hideous.

Just not viable to clad the front, more doable at rear, but as you say, roof extension needed on both eave & gable. 

I guess the exercise would cost north of £20K. Maybe 40 year payback in financial terms. Probably a similarly tenuous payback in emissions. Not exactly a low hanging fruit.

More realistic, perhaps, to insulate internally, piecemeal, as rooms are redecorated.

Actually, internally, the Victorian builders put spaced lath & plaster liners, inside the solid brick walls. It seems to be unusual, the EPC box-ticking exercise hasn't a box for it, and a cursory online search didn't show me any performance figures for it. It does feel significantly more comfy than simple solid brick & plaster. 

Andy C: 
. . .

Interestingly, I am currently involved with a major project for a local businessman where we have installed a large ASHP setup to heat his house which he is extending. Despite not being short of money he has been moaning about the ASHP running costs (currently £20-30k/year). Due to large areas of glazing he also wanted a/c to cool about 14 rooms so we've fitted a VRV system which enables it to extract heat from those rooms which need cooling and dump it into the hot water or heating systems. Result, free hot water! 

I feel this would be a better approach for heating houses than trying to get heat pumps to replace gas boilers. Should we go down the road of the USA with new houses having central air systems ducted to each room? Should be better and more efficient than trying to heat up water/floors through UFH and allows for cooling in those sweltering hot summers we get!

When we moved to Hampshire, in the mid-1980s, we saw ducted air heating installations in several houses, including in the one we eventually bought. The good point of this system was, to my mind, the speed with which a cold room could be warmed up from cold. Open the sutter for that room and one could feel some benefit almost immediately and it would not take long for the whole room to feel warm. Whereas turn on a radiator and can take a few minutes for the radiator to fully warm up, and it takes rather longer to fully warm the room.

Human nature comes into this. I think one reason why people sometimes keep heat on in an unused room is a precaution against suddenly deciding to use the room and needing to suffer the cold before it warms up.

There are some downsides to ducted air heating. One is it can be a bit noisy. In our lounge then, the outlet was smack between my stereo speakers; not appreciated when I wanted to listen to hi-fi music. Another is that this system can be easily designed and built into a new house but adapting to an older house, like our present 1950s-built house with radiators, is less easy and probably very expensive.

One often hears the USA criticised for being one of the world's biggest polluters, but I think the Americans are onto a good thing here. A flexible heat-pump system, which can also cool the house in summer and use the heat to heat water! In their language, that sounds just swell! Let's have it over here. 

You need to see the proof? Here it is, very well expressed.

Andy C: 
. …. Should we go down the road of the USA with new houses having central air systems ducted to each room? Should be better and more efficient than trying to heat up water/floors through UFH and allows for cooling in those sweltering hot summers we get!

There are two goals with such a system. One is heating. The second is clean fresh air. They do conflict with each other some. Air circulating purely internally is best from a thermal point of view, but you need some way of (at least) extracting CO2 and adding O2. The easiest and least costly way of doing that is air exchange with the outside. There has to be some heat exchange at the interface. There are fairly straightforward ways of doing that, and I know what is claimed for them in the literature, but I am not at all sure that how it works out in practice is near how theory says it operates.

I don't see that ducted hot air is any more thermally efficient than other methods. Let's stick with heating. If your house has a general indoor temperature of X and the outside of Y < X, then your house is going to be radiating into the environment at a rate given essentially by Y-X plus the insulating qualities of the interface (walls + roof + ground under the house). Ducted heated air or underfloor heating or hot radiators or space heaters or whatever, that is a question of distribution and what occupants are most comfortable with, not of thermal efficiency. (I agree that comfort is the main factor for those who can afford their heating bills in the first place.)

Denis McMahon:

When we moved to Hampshire, in the mid-1980s, we saw ducted air heating installations in several houses, including in the one we eventually bought. ……..

There are some downsides to ducted air heating…… this system can be easily designed and built into a new house but adapting to an older house, …..is less easy and probably very expensive.

There are individual devices for individual rooms which exchange air with the outside, and which exchange heat during the air exchange. They are not large. The specs for one device I have been looking at are roughly 38cm^2 cover, sticking out 5cm into the room (you get a 35cm to 60cm hole in your outside wall). They claim 82% thermal efficiency through heat exchange, and you can get them to exchange 15 m^3/hr to 55 m^3/hr for the same wall space. They are not noisy – claimed 25dB at 30 m^3/hr.

You just have to find that 38 cm^2 patch per room outside wall. 

It solves both problems of course: heating and air exchange.

One often hears the USA criticised for being one of the world's biggest polluters, but I think the Americans are onto a good thing here. 

It is not just the US. HVAC knowledge spreads around the first world as fast as any engineering.

davezawadi (David Stone): 
 

You need to see the proof? Here it is, very well expressed.

More guff. First, Monkcton is a classicist with a journalism degree, not a climate scientist. 

Second, the Heartland Institute is not a centre of expertise on climate science. It is, rather, a contrarian think-tank which has addressed a variety of general scientific/technological issues arising from market failures, such as DDT, the link between smoking and cancer, and of course global warming, in a manner contrary to the consensus of (real) scientists.

If you really want to get into detail on the guff, let's do it point by point. 

Point 1. It apparently impresses you that the Mauna Loa measurements of CO2 didn't show the dip you seem to have expected in 2020. 

First, do you know how much global emissions of greenhouse gases reduced in 2020? Second, how long would you expect a reduction (of that magnitude) to show up in the Mauna Loa readings? (And, third, please justify those assertions by reference to the scientifically-reliable literature.)