ASHP + two cylinders - possible?

Dr. H · 2025-02-13T15:36:24Z

Hi All, I will be having an ASHP fitted this year. We are a family of four who occasionally host one or two guests. There's not a lot of space available for a cylinder (we can squeeze in a 200 litre one), and I was wondering if it might be possible to combine a conventional cylinder that supplies all the bathrooms, with a Heat Geek Mini-Store in the kitchen to supply kitchen sink, hot-feed dishwasher and washing machine, and downstairs w.c.. The mini-store and hot water cylinder would be installed on the same ground-floor level as the heat-pump, which would hopefully make pipework straightforward and I'm hoping it would just be a matter of a suitably-configured controller and valves to make this setup work. At the moment I'm thinking of going with a Mitsubishi Ecodan heat pump but if going with another brand would help to make this work then I'd be willing to consider that. Thanks for reading and any thoughts gratefully received!

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Air Source Heat Pumps (ASHPs)

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Toodles

(@toodles)

Illustrious Member Contributor

Joined: 3 years ago

Posts: 2475

14/02/2025 3:21 pm

@dr-h My dealer may have believed what he had been told, but………. 😉Toodles

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

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BobTSkutter

(@bobtskutter)

Estimable Member Member

Joined: 1 year ago

Posts: 94

14/02/2025 5:36 pm

@dr-h

I'm not a heatgeek professional (although I am a geek 😉 )

The heatgeek "pink cylinder" is a thermal store with a coil inside. The water from the heating circuit is on the tank side, the potable water from your water supply is inside the coil. The coil is very long and has a large surface area so it will heat the water as it flows through the pipe. If your central heating system has a suitably sized accumulator you won't need an extra one for the "pink cylinder".

The design is similar to what I've seen installed on solid fuel systems, although it's colour is a little brighter!

The hot water inside the cylinder would need to be a relatively high temperature, probably the same as your actual hot water tank. So you'd need a control scheme that could divert the central heating flow into the cylinder and increase the heat pump flow temperature.

I might suggest if you're concerned about hot water flow then you might want to make sure you have back up immersion heaters in your main water tank. I have a doubts that a heat pump is really to way to provide lots of hot water and heat a building at the same time. You could install two heat pumps, one for space heating and one for water heating. That would make the controls much easier since the two cylinders would be zones off one heat pump.

This might be an interesting read for you:

https://renewableheatinghub.co.uk/forums/domestic-hot-water-cylinders/double-heat-pump-for-dhw/paged/3#post-41158

Regards

Bob

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