Is internal wall insulation worth it on a cavity wall?

[Colin Green]

Mmm, you could take that argument for any thickness though; it's more like the first X millilmeters stop Y% of the heat loss, the next X millimetres stop Y% of whatever the first X mm didn't stop (so if 100mm stops 90%, 200mm stops 90%, plus 90% of the 10%..)

..I don't think it's ideal to assert that some particular thickness is a magic perfect amount beyond which it's diminishing. The ideal amount is contextual, rather than a fixed value

50mm only because that's probably what is in there and probably what I'd fit on the inside. 50mm because that's a standard size.

 

[foxhole]

It is important that heat pumps are only installed in insulated buildings, this is because the lower the flow temperature from the heat pump, the higher it's efficiency. In a poorly insulated building a higher flow temperature is required meaning the heat pump will cost more to run and have higher carbon emissions.

 

[robinbanks]

(and fine attention to draught-proofing plays a vital part in what foxhole said too; one can have walls that are foot thick kingspan, but if they leak air like a sieve it's about as much use as piling the kingspan up in the garden)

 

[flameport]

It is important that heat pumps are only installed in insulated buildings, this is because the lower the flow temperature from the heat pump, the higher it's efficiency. In a poorly insulated building a higher flow temperature is required meaning the heat pump will cost more to run and have higher carbon emissions.

All of that also applies to a condensing gas boiler.

 

[omph]

Only true when they supply underfloor heating, just as with any other heat source for UFH.
Radiators and a heat pump can be used in the same way as radiators heated by gas boiler, oil boiler or any other heat source.

Not really. When installing HPs, heat loss calcs and rad upsizing is part of the process.

Maximising efficiency is important since gas is 3.1x cheaper than electric, hence a minimum COP of 3.5 is required if you want to save money. Running it 24/7 at lower temps (ideally under 30c) with weather comp is more efficient rather that running it say 5 hours a day at higher temps (50c+) which will give you a much lower COP, and most of that heat will be used to heat up the walls before you feel the effects which means you'll have to dial up higher. HPs loose efficiency quickly at temps above 45c and end up costing a lot more than gas. With that said, running it 24/7 is also dependant on individual lifestyles, and how often a person is at home etc but the general principle is lower temps and longer run times.