ReedRichards

I'm not sure that foam insulation is suitable for outdoor use. It's certainly not the type that is usually used.

I'm not @Dan F but my thought is that this is more about the temperature you want to achieve. If you like your house to be a bit cooler overnight then use the set-back mode. If you like the same temperature 24/7 then don't.

Sorry, you've lost me there.

Surely it's just about the amount of warmed water you have per unit area of floor? The closer you make the pipes then the more warmed water per unit floor area so the more heat it can give out for any given water temperature. Since what you want is a fixed amount of heat for any given outside temperature then the closer the pipes the cooler you can make the water so the more economically you can run your heat pump (provided it's not also having to provide heated water for radiators elsewhere in the building).

I'm curious, @TheMitchells, what happened at this discussion? You had some rooms where you would certainly need to increase the size (or number) of radiators and that would take some ingenuity.

Really? My heat pump is right next to a drain which carries rainwater off the roof to a soakaway. Hitherto I had thought that precluded my getting an R290 heat pump when my existing one needs to be replaced.

In the spreadsheet the installer has (stupidly) entered 100% in the "% Demand met" column instead of the actual figure, which is the number in the "Total Output" column divided by the number in the "Power loss " column. So the worst case is the Bed 1 En-Suite where the figure is 293/290 = 101%. The lounge isn't much better 2391/2306 = 104%. On the other hand the kitchen 1176/768 =153 %. You would need to add a third radiator into the lounge of much the same size as the other two and squeeze a second radiator into that ensuite with about half the output of the towel rail and you would be on your way to achieving the capability to run at a lower flow temperature. Aim for all the numbers, calculated properly, to be 150% or greater. Another option (as suggested by others) is the use of fan coil radiators but they need both plumbing and electrical power so they make the installer's job quite a lot more involved. If you want to talk about anything with the installer tomorrow (i.e. at short notice) ask them what they think of those.

If you retrofit an ASHP then under many circumstances it qualifies as a Permitted Development. But that only applies if you don't use it for cooling. Of course if it is part of a new build then the planning permission will encompass the heat pump and you can do what you like with it, heat or cool. I presume @Dave Joneswas in that situation so his ignorance can be forgiven.

I would be surprised if you can get a quote for fan coils as part of the installation. As it's a retrofit you could not use them for Air Conditioning without planning permission. And you have to not mind the fan noise.

For some reason I'm not able to download the pdf files attached above. Is there a trick to do that?

You mean kWh but yes, it means that the heat demand calculation is either wrong and/or it's based on keeping the house warmer than you actually do and/or last year was milder than the calculation suggests. Most of your electricity usage will have been for heating and hot water and I don't think these calculations ever agree perfectly with actual numbers.

What you are trying to achieve is the best compromise between (maximum) flow temperature and radiators you can fit in the available space. The lower you can make the flow temperature, the more economical your ASHP will be to run but the larger will be the surface area of the radiator(s) needed to heat each room. A radiator specified to run at an average of 15 degrees above room temperature needs to be 2.5x bigger (in surface area, essentially) than one specified to run at an average of 30 degrees above room temperature. The latter is roughly what you would have with a 53 C flow temperature.

Because? Why bother insulating those pipes if you're not bothering to insulate any other pipes within the heated fabric of the building?

One thing you have to be careful about when determining the optimum size of your heat pump is software limiting. I believe it's quite common for a manufacturer to sell the same heat pump as, say, a 4 kW , 6 kW and 8 kW model where the only difference is a software-imposed maximum. In which case there is no disadvantage to getting the highest power model as all three will have the same minimum power.

Technically, you have to be careful about condensation Administratively, an ASHP installed as a retrofit does not usually require Planning Permission if only used for heating, but it does need Planning Permission if it is also used for cooling. Those are my guesses.

I still think it's genuinely a good idea. With a wood burning stove you start off too cold, light the stove, wait an hour and thereafter you're too hot for a while longer than you keep feeding the stove. It can be a very pleasant too hot but you inevitably end up hotter than you need to be. The air-to-air heat pump lets you quickly take the chill off a space then keep you as warm as you want whilst using only a fraction of the electrical energy that you get back in heat.

Air-to-air heat pump? Highly efficient and particularly good when you don't need the massive amounts of heat that a wood burning stove would give.

If you want all the rooms in the house to be at the same temperature 24/7 there are no downsides.

There has been recent publicity about a hot water unit that really would fit inside a large kitchen cupboard. See But it's very much untested in real domestic settings, so far.

I have considered getting one of these but because the pump needs to be suitable for potable water it would seem to be prohibitively expensive. Any thoughts?

This is from the Fact Sheet for the (old) RHI application: But that was for one particular grant scheme.

So do we need to find another liquid we could wash/shower in that doesn't require so much energy to make it warm/hot? I guess it would have to be filtered and re-used but that doesn't sound impossibly difficult and heat recovery could form part of that process.

"Tat"? I presume this is a spelling error rather than a disparaging remark?

In 2020 I was told that my EPC needed to be less than 2 years old. Have the rules changed since then?

I think this is a very useful comment. Don't be distracted by the size of heat pump you need but first focus on whether you have enough heat output for your double height area. When you have sorted that out, then you can get back to recalculating the heat pump size.