Posted by: @billsp44

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I am about to install a heat pump in my 1930s detached house. However my mains gas Vaillant combi is only 7 years old and still going strong… Should I wait for

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I would bet this does not hit the market before the current period of the gas boiler upgrade scheme, that is running until May 2027 offering £7.5k (if you decommission a gas boiler). There´s no guarantee that this will be extended with the same terms. 

In terms of running costs vs current, you may want to assume a well tuned ASHP will have an efficiency of 3.5-4.x. Assuming you can access decent electricity tariffs, you reduce your bills and also stop indirectly propping up dictators straight away. 😀 

Not entirely! Electricity generation still involves a very significant amount of gas – I keep a watch on it every day through my GivEnergy app… Also I have long runs of 10 mm copper to my radiators. Whilst there’s no guarantee, this new technology looks like it just might be a drop-in replacement for a Combi… Too early to say of course. But without wishing to spend thousands on repiping one only has to read the horror stories on this website to realise that anything short of the ideal in heat pump installation is a risk.

We already have a helium shortage so presumably they have to get this from "neat trick with helium" to product made with cheap gasses. Given how long it takes to get anything into production at scale and then make it actually work properly (usually later, the tech industry calls early adopters "the suicide squad" for a reason) I guess it'll be arriving somewhat after V2G and solid state batteries!

I take the point about the scarcity of helium gas - though the prize of a technology 30% more efficient than air to water heat pumps does seem worth striving for… better read your new book after all…!

Posted by: @billsp44

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I take the point about the scarcity of helium gas - though the prize of a technology 30% more efficient than air to water heat pumps does seem worth striving for… better read your new book after all…!

I think the best advice is - if you want a heat pump get a heat pump.  Even though the underlying technology is over 100 years old, its application to domestic heating is still maturing a bit, but its sufficiently mature that the rate of change is slow and its definitely already good enough for real world use.  With the help of people on this forum, the installation can be de-risked almost completely if you are prepared to share some information.  The majority of people who get a heat pump are happy with it, at least according to the only large scale survey we have - from NESTA in 2023.  Actually its about the same percentage (~80%) as are happy with their boiler!  Of course that's not good enough in either case, which is why this forum exists.

If you don't want a heat pump, then it doesn't matter what reason you use to delay, and should you change your mind in the future the technology will be what the technology will be. 

10mm pipework is not necessarily a problem, it depends on the heat demand.  You certainly should not assume that re-piping is necessary.  If you are interested and wish to provide some more detail for a bit of an initial view then please do so, there are people here who will be only too pleased to help.

Posted by: @billsp44

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... though the prize of a technology 30% more efficient than air to water heat pumps does seem worth striving for… 

Yes and no.

To me, this is a classic case of excellent fighting against good. With heat pumps already delivering three and a half times the energy they consume, the problem is not one of efficiency; it's the financial problem of electricity being around four times more expensive than gas. Certainly, an extra 30% jump in efficiency would be a good thing and certainly well worth investigating but it won't IMHO be the game changer a levelling of fuel prices would be.

Given that huge disparity in fuel prices can be tackled very effectively right now with home batteries, time of use tariffs and solar PV where possible, I would say waiting for a new and unproven renewable heating technology is not the strategy I'd pick.

@majordennisbloodnok 

Absolutely and with efficiency being even better with a2a heatpumps, where there’s a will there’s a way..

Posted by: @batpred

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@majordennisbloodnok 

Absolutely and with efficiency being even better with a2a heatpumps, where there’s a will there’s a way..

I agree.

So far as I understand, we can't necessarily say that efficiency of A2A is better than A2W - everything I'm finding out suggests it's all in the specifics of the property and of the installation - but they both seem to be of a comparable scale and so can both be included pretty much as one item in the view I've put forward.

@majordennisbloodnok 

I just noticed that A2A manufacturers tend to quote higher efficiencies than A2W. In practice the fact they inherently have no defrost cycles can only help.  

But agreed that it depends on the property and installation. 

Posted by: @batpred

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In practice the fact they inherently have no defrost cycles can only help.

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Is that correct? I was under the impression that some A2A systems just pause the internal unit whilst a defrost happens but that the outside unit does still have to go through a defrost cycle. I'm happy to be corrected, though.

Posted by: @majordennisbloodnok

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Posted by: @batpred

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In practice the fact they inherently have no defrost cycles can only help.

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Is that correct? I was under the impression that some A2A systems just pause the internal unit whilst a defrost happens but that the outside unit does still have to go through a defrost cycle. I'm happy to be corrected, though.

 

I dont think it is correct, given that @ashp-bobba described how the defrost cycle of an A2A het pump works just a few weeks ago.