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Advice on my Heat Pump Journey: Old Stone Built Detached Cottage

PaulC · 2026-07-20T07:49:04Z

Hi All I have just received the book "The Ultimate Guide to Heat Pumps" and I note that there is a forum that could provide some advice. Therefore, can any members please provide some advice on my air source heat pump installation journey, I live in an old stone built detached cottage (now a house) which was greatly extended and modernised in 1984. The existing heating system was an oil boiler which was replaced by an external Worster/Bosh Dainsmore 25 boiler with new Joule insulated 200ltr unvented hot water tank, In 2017. This is a 3 pipe pressurised system for the heating and hot water using 22mm pipework for the main feeds and 15mm pipework to the radiators. The radiator circuit is one circuit controlled by a single solenoid valve with a common variable speed pump for the heating and hot water circuit. The hot water has its own solenoid valve all is controlled by a Nest system. About 70% of the radiators have TRVs. The house has had new double glazing and doors and the heat loss is low as we have 200mm insulation in the roof. I have calculated the heat loss using individual wall U values (something I use to do some years ago as an electrical engineer in my consultancy days). Total heat loss is about 5.7Kw without taking into account the hot water cylinder consumption but I usually heat my water overnight on the cheap rate. I have had some proposals where its just an arbitrary quote, but I have had one quote where the house was surveyed, and I was quite impressed by the installer but not so the quote due to the lack of technical detail. The proposal I am considering and where I need some advice is as follows: The proposal is to install a 10 kw Heat Pump using the R32 Midea mono air-to-water unit. The outdoor unit incorporates the main control board, modulating pump, a 7-litre pressure vessel, and a 3-bar pressure relief valve. In addition, they have proposed to install a Heat Saviour unit that enables any manufactured heat pump to work with an existing heating circuit. The Heat Saviour unit consists of a 20-litre volumiser, a plate-to-plate heat exchanger, and a 3KW heating element, all designed to sit beneath an unvented cylinder within a standard 600 x 600 mm airing cupboard. To me this looks like it provides minimal disruption to the existing heating and hot water system but my question relates to the Heat saviour volumizer and plate heat exchanger as I am concerned that this has quite a low volume of Glycol and I presume runs at a high pressure. Does anyone have any experience with the Heat savour product or a plate heat exchanger and this type of proposed installation what are the pitfalls if any and will it achieve a SCOP above 4 ? do I need to ensure means of displaying the system delta T and should I be asking for some sort of guarantee. Any advice welcome Also does anyone know of any other good installers in the Bristol area? Please let me know if you have any questions or require further clarification.

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Air Source Heat Pumps (ASHPs)

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EtchedPixels

(@etchedpixels)

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22/07/2026 8:12 pm

I would also look at an air/air install if you've got to make radiator changes, you want cooling or you want to migrate over time (ie keep the gas too). A lot of that is taste though but even if you don't want air/air having an air/air quote to wave at the air/water people never hurts 😉

Whichever way you go the essence is simplicity. Every extra box, widget, magic contraption, valve and whatnot increases the cost and decreases the performance and the reliability.

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