New gas boiler, your thoughts welcome

Yes, you can get 60°C flow from an air sourced pump but the CoPs drop significantly - 3 to 1 is probably realistic at that high a flow temp, even with fairly warm (i.e above 10°C) intake air.

I’m no expert - just an “interested” owner of a heat pump system but I’ve posted quite a bit of data on these because there is much more to sizing a heat pump than just looking at the “headline” CoP and max heat output figures.

That said, although they are not perfect air source heat pumps are a good way to heat a home if you want to have a moderately “eco friendly” solution.

I’d be very interested to know the exact model of the LG you mentioned - at some point I’ll be looking to change the boiler in the UK and had started to toy with whether I could make a heat pump work here, having access to a high flow temperature if it does not impact efficiency too much moght be useful.

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Don’t let go of what you know, whilst they can reach higher temperatures flow and efficiency must drop, law of physics. Marketing in ideal laboratory conditions etc.

My guess is that 80°C can only be reached with auxiliary heating - in fact 60° can probably only be reached with additional heat. My heat pump has a 6kW heater, it isn’t there for decoration.

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The model for the higher temperature LG unit is the Therma V high temperature unit. It can reach a flow temperature of 80°C by using two stages of cascade compression. It doesn’t need any auxiliary heating but the COP is considerably less and may be only 2.1. This is still going to be more efficient than oil or gas but I’m really not sure it would be worth it unless your main concern was your carbon footprint.

If these units did have any form of auxiliary heating, then this would have to be taken into account in the quoted COP values.

With any air to water heat pump, they are best operating at low flow temperatures to get the best COP, so typically 45°C for radiators and 35°C for underfloor heating, so if you have underfloor heating then it’s the perfect most energy efficient method of heating with a COP approaching 5.

All of the COP’s stated by all manufacturers for their heat pumps and the like are under perfect conditions where you will get the best COP readings, so -3°C to 10°C outside conditions to the lowest flow temperature possible.

The only way you will find out how efficient these units actually are is to install one to determine the true efficiency over an entire year (seasonal efficiency). Apart from that you’ve got to consider what flow temperature you are going to run at and understand that the COP quoted is the best possible and in reality you just aren’t going to get that. It’s a bit like the quoted mpg values for cars.

It’s a difficult choice to make, heat pumps are ideal for new builds but an awful lot needs to be considered for a retrofit in an old property.

OK, yes - manual here, There seems to be just one high temperature unit in the range which has a CoP of 2.61 at both A-2W65 and A7W65 which is reasonable I suppose. Otherwise CoP’s seem to be just over 4 with 7° air and about 2 with -2° air for a 55° flow temp - again not radically different to any other unit on the market.

I did some back of the envelope calculations in the previous thread which suggested a “seasonal average” CoP of 3.6 would reduce your COs footprint by about 20% but probably cost more to run than a gas boiler - at least in the UK, for mains gas.

Your comments re underfloor heating being well suited are spot on, of course - as are your observations that it’s a complex decision if replacing a conventional boiler in an existing system.

We have looked at a Jotul and I would like a hotplate on whatever we get if only to put a kettle on. Any recommendations or what to avoid would be welcome thanks.

Yes Paul, the law of diminishing returns, usually linked to the inverse square law at which point friction takes the rest.
I believe we’ll need a break through in tech to get to the next level. Rather like the breakthrough Toyota have made, by accident that a li-ion battery can be vastly improved with titanium. not bad for a company that thinks batteries won’t make it so back hybrid.

More efficient air-con units using a desiccant are on the way so only logical something in the heating dept could follow.

I am still considering evacuated tube array for pool and underfloor in winter with a small top up of some kind.

Anything with a flat top and not made in France for the last 100 years should suffice.
Worth looking at the DEFRA site for recommendations of cleaner burning more efficient stoves. Plenty of Jotul’s and others.

The EU stove alliance regs due in 2022 should shake up the market but I doubt some countries will change despite rules.

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Thank you.