[leoedin]

The other issue is that a heat pump has to keep the output temperature relatively low to stay efficient - so just dropping a heat pump in to replace a wet heating system with a gas boiler will have two problems - the total power is less, and the amount of power the existing radiators can deliver to the room is too low. Effectively heating a house with lower temperature water needs big radiators or wet underfloor heating.

[blitzar]

"The Daikin Altherma 3 H HT air source heat pump can provide water with temperatures up to 70°C – the same level as gas boilers – and can work when it’s as cold as -28°C outside."

https://www.theecoexperts.co.uk/heat-pumps/high-temperature-...

Given that there are a lot of existing houses out there, surely drop in replacements should be more prevalent.

[sokoloff]

It can make leaving water temps (LWT) of 70°C. It can work when it's as cold as -28°C outside.

What it can't do is both at the same time: make 70°C LWT when it's -28°C outside. It's designed for 65°C LWT (some models 60°C) and can only reach 70°C at a performance penalty (year-round) and can only maintain 70°C LWT down to -15°C and starts to lose max LWT, heating capacity, and even more efficiency below that. (Losing efficiency a few days out of the year is a minor concern. Not being able to meet the heat loss and heat transfer for the building for a few days is a much more serious issue for health and comfort.)

[hedgedoops2]

Heat pumps can't be more efficient than the theoretical Carnot heat engine running in reverse, whose efficiency is T_outside / delta_T. In this case it's (273-28)K/98K = 2.5.

I guess being 2x as efficient (cheap) as electric resistive heating isn't super-terrible, but it's not great either.

Compare this to a favorable groundwater heat pump configuration with good radiators and insulation where the 'outside' (groundwater) is maybe 10°C and the target temp 30°C (close to room temp): (273+10)K/20K = ~14.

[Tor3]

That article was generally informative, but they forgot (as far as I could tell after a quick read) to include something very important: How much heat can that Daikin heat pump provide? 3kW? 6kW? 10kW? Can it provide more than a standard air-to-air heat pump which typically can provide less than 7kW under optimal (read: Not that cold outside) conditions? This is important to know before buying one (any type of heat pump)

[blitzar]

"from £12,500" I guess it comes in different sizes

To be honest the prices I see out there are still generally 'luxury' anyway. If i am spending £20k on a boiler, then an extra £2k to have a secondary gas system that never/very rarely gets used wouldn't bother me at all.