Large heat pump options for church building

Air Source Heat Pumps (ASHPs)

Last Post by Toodles 2 hours ago

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Josephiah

(@josephiah)

Trusted Member Member

Joined: 2 years ago

Posts: 35

Topic starter 27/09/2025 7:09 pm

Hi everyone,

We're coming up for 2 years with our home heat pump (Vaillant Arotherm+ 12kW) / solar / battery and have been very happy with it all. I am now looking at the energy use of our local church building and wondering about doing the same on a larger scale there.

Very early stage, and yet to do a proper audit of energy use / heat loss, so really just scoping out options.

A few initial characteristics, to be surveyed properly in due course:

Building is fairly modern, opening in 2006, so should be fairly well insulated; however, it does have a very large outer surface area.
Large auditorium (3-400 capacity) plus various other smaller rooms.
In use all week, with cafe running every day.
Currently has a 100kW Vaillant gas boiler running off Calor gas canisters(!), as was deemed too expensive at the time to connect to gas network. This replaced the original oil heating, but not sure how long ago.
Under floor heating in auditorium and whole of ground floor; radiators in upper floor rooms.
Lots of roof space for solar 🙂
A bit of land surrounding, so ground source potentially also an option.

So the first questions for now are:

What makes/models of ASHP would come recommended in the 50-100kW range? (No idea yet how oversized the current boiler is - to be determined.)
Is the decision between ASHP and GSHP mainly based on up front cost vs efficiency? Or is there also a crossover with size, where getting source becomes more sensible?

More questions to come in due course, no doubt!

Thanks,

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Toodles

(@toodles)

Illustrious Member Contributor

Joined: 3 years ago

Posts: 2125

27/09/2025 7:23 pm

I should think that a heat loss calculation might be a wise first move; with good insulation in a modern building, you may well find you are looking at heat generation less than 50 kWh as at present, you are presumably kept warm enough with the 100 kWh system that’s probably no more than ~90 % efficient. As to GS versus AS, I would not like to comment as I have no experience for comparison; bear in mind that GS will involve extensive digging up of the ground to install the ‘slinkies’ or other pipework system. Good news about the real estate to cover with solar panels - go for it! The most expensive component for the solar may be energy storage of course. Regards, Toodles.

Toodles, he heats his home with cold draughts and cooks his food with magnets.

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