With gas boilers potentially being banned in new homes from 2025, should we look at alternatives now

This is the thread you want to read, over in LPG, Heating Oil, Solid & Other Fuels


Air Source Heat Pumps/Air Con - Full Info & Guide
https://forums.moneysavingexpert.com/showthread.php?t=1464827

Personally, I would get a gas boiler while they are still readily available. I don't think they are going to ban existing gas boilers for a very long time.

I have been thinking about this although our boiler hopefully has a few years left. The issue with heat pumps seems to be the requirement for lower temps to acheive sensible efficiency resulting in a requirement to replace all rads and pipework and even then it is unclear whether an average cop of 4 needed to make the cost competitive with gas can actually be achieved.

Gshp has a higher fit and more stable cop but the numbers only seem to work for trench install which we don't have space for even before the cost of a replumb.

Battery/large hot water tank storage of cheap overnight leccy plus individual room ashp might give different numbers again....

It depends, the price of GSHP and to a lesser degree ASHP will fall given time (R&D) and as a result of increased market penetration. There was talk about purpose built drilling systems that hit a better value for money point on bored systems.

On the other hand the RHI won't last forever and if you can qualify for it then it makes a huge difference to payback times.

If you've got cash laying about then I'd say yes do it now. But if you're trying to retrofit into an older property it's an epic job. I've got it pencilled in for 2021 or 2022.

So I am trying to do the maths.

Let us exclude purchase and install cost for now (assume it will be covered by RHI) for the sake of simplicity.

WE currently use 32000 kwh of gas a year.
Looking at monthly usage I am guessing about 1000kwh per month for hot water and up to 4000kwh for heating in the coldest months. I straight divide gives daily usage of 133kwh or 5.5kwh per hour but of course individual days might be even colder so we might need constant heat output of 8kwh per hour on the coldest days.

I don't know how efficient our boiler is - in theory it is condensing and modulating so will mostly run at its most efficient. It can output between 5kw and 19kw, the heating curve has a return water temp for heating of 30C when the outside temp is 10 degrees up to 70C when it is minus 10.

First issue is therefore obvious - heat pumps are not efficient with water temps of 45 degrees (?) suggesting that our heat emitters (radiators) are not sufficient for the water temp. We could obviously upsize to improve heat output at lower water temps (change doubles to triples etc) but it is still unclear if this would be sufficient and then there is still the question of circulation - I know a fair bit of the upstairs is only 15mm pipe not 22mm.

Our hot water tank is 190l which we heat to 60 degrees. In an hour in the morning we typically run off one bath and 5 showers - say 4-500l? If the incoming water temperature is 15 degrees that means we drain the whole tank and also use a fair bit of the boiler output to achieve this. (approx 12kwh stored in the tank plus 5kwh from the boiler to provide 17kwh worth of hot water from 15 degrees to 40 degrees).

If the boiler is cooler (to max heat pump efficiency) then obviously we would need to provide more of the heat 'on the go'. There is also the question of legionella if the water tank is not at least 60C once a day.

So it looks like we might need either a bigger hot water cylinder or heat pump output of at least 19kw as we have now with the gas. At a COP of 1 (coldest days or direct electric back up) this is 80A which might be a problem with a 100A supply and other use.

Putting all this heat demand together means we might need a heat pump system able to output at least 12-15 kwh per hour however cold it is outside.

WE pay about 3p per kwh for electricity and 12p per kwh for gas. The big question is then what are the relative efficiencies. For heat pumps this info seems pretty thin on the ground for either ashp or both types of gshp. it is also unclear what the losses are for gas hot water and heating.

Is COP 3 for ashp, 3.5 for ground trench and 4 for ground vertical loop reasonable? How about for the efficient gas boiler - 90%?
32000 x 90% = 28,800 output demand
32,000 x 3p = £960
28,800/3 (COP) = 9,600 x 12p = £1152
28,800/3.5 (COP) = 8,230 x 12p = £990
28,800/4 (COP) = 7,200 x 12p = £864

Given the amount of energy involved there seems to be very little scope for time shifting demand to off peak electricity rates using battery storage. Even storing the hot water heat in a large hot water cylinder seems to have limited scope due to the lower temperatures for high efficiency.

So the only thing that seems to make sense might be a vertical loop gshp, problem with this is the install cost, high 20k plus whatever is needed to make the radiators work and address the legionella issue with an RHI that seems to be at most 20k over 7 years.