My DIY Heat Pump installation

Polar bear · 2025-11-03T16:35:32Z

Hi All New to the forum. I did post earlier in the year saying I was going to post the details of my DIY Heat pump installation but its been a busy year and not had time to do it. All finished now and so here goes. The background 5 bedded detached house, the oldest part built in the early 1800's with various extensions over the years, was initially 2 cottages converted in to one house in the 70's. The last extension was by us of a big kitchen diner in 2010. Locality is South Lancashire, walls are mainly solid in older part through to insulated cavity in the new extension. I have insulated as much as I can and double glazing fitted about 10 years ago. Complicated heating as mostly done in the 70's, essentially the left hand side of the house (LHS) (was one of the cottages) is radiators all fed from a manifold terminating in 10mm microbore to the rads, right hand side (RHS) is similar to rads. New extension is UFH downstairs and radiators off a manifold fed by 15mm pipe. I replaced all the old radiators with type 22 about 5 years ago. House was heated by oil when we moved in but at the time of the extension in 2010 I decided that oil was bad and going to get expensive so decided down the route of ASHP then. Very little info about then so decided along with my plumber/electrician to DIY then. Got 2 ASHP one 8.3KW and the other 11.3KW off the internet for about £ 1,500 each. The initial set up was the 8.3 unit was to do the hot water (DHW) and the 11.3 the heating. After a short while it was obvious that the 11.3 was struggling so on contacting the seller he suggested linking the two via a LLH and having zone valves controlled by thermostats and separate pumps to LHS, RHS, UFH and DHW. So this is what we did and it worked.....sort of. Over the years the house was kept warmish and the DHW was OK and topped up by immersion as necessary. It started getting expensive however and with the price of electric going up, very expensive. I also realised that the ASHP were nearly 15 years old now and not as efficient as they had been so all in all needed upgrading. Looking at various links I was loathe to start spending tens of thousands of pounds on a new system and didn't want to go down the route of MCS with all the hassle. It is an old house and I didn't want people who I realised may be didn't know what they were doing coming and giving me bad advice. So, I decided to do it myself, everything was there, it maybe just needed tweaking. I was lucky as I know an ASHP engineer who gave me some advice and my wife's cousin is a plumber who is now specialising in refits of botched ASHP installations, he also gave me advice. Jan 2025 I was researching ASHP on the internet and getting quite shocked as to how much they cost, my old system came to a total of 19.6KW and I did a rough heat loss calculation off the internet and reckoned a 16KW system would do me. Other friends who had similar size houses and had spent £15K on installs had similar size models so it looked OK. As you can see all of this is generally 'back of an envelope' type stuff. Then I found on ebay a brand new 16KW ASHP for £ 850! Far too good to be true and so the old adage of if it's too good to be true...... But I researched the company and got in contact, turned out they were a heating company in Wigan who's former CEO had bought 20x 16KW ASHP and 20x 9KW ASHP from China with a view to fitting them in to peoples homes. Trouble was he then realised he would have to send his engineers to China to get trained in how to fit them properly and this wouldn't be cost effective, so he was stuck with 40 ASHP. This is maybe when he became the former CEO. So I googled the ASHP, got in contact with my contacts and looked in to it. Downside was bought as seen, no warranty and no real advice as to how to fit them. But I thought for £ 850 I could take the gamble so I trundled over there with my trailer and a very nice lady driver in a fork lift truck plonked a brand new, unopened 16KW ASHP in and I bought it. Foshan AIROSD 16KW DC abd EVI inverter ASHP, Monobloc unit with R32 refrigerant. When the heating season was over I disconnected all the old plumbing and placed the unit in a new position outside, my electrician came and connected it but this was very straightforward as all the old wiring and controls were there from the previous ASHP. After reading lots of blogs and forums such as this one I decided on the following set up. No LLH, all run as an open loop system, the LLH is still there in the return pipe but plumbed as a 2 way LLH and is essentially a dirt and air seperator in the return pipe. All zone valves taken out for LHS, RHS and UFH. All room thermostats disconnected I still have the seperate pumps for LHS, RHS and UFH, so now a Salus pump set on highest constant pressure curve feeds 28mm pipe to three sperate zones, LHS with additional pump set at velocity 1, RHS with pump set at velocity 1 and UFH with pump set at velocity 1. I was...

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Air Source Heat Pumps (ASHPs)

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Polar bear

(@polar-bear)

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Joined: 10 months ago

Posts: 8

Topic starter 05/11/2025 4:33 pm

@bontwoody

My plan is to run the flow temp at about 35 degrees by varying the return temp according to the outside weather, I will have to see what inbuilt weather compensation the ASHP has for this when it gets really cold. That way I can run the UFH and rads at 35 degrees and will vary each room via the lock shield (all TRV are set at fully open) if they are getting too warm. To be honest it would be nice to have the problem of having to turn the heat down as this is not an issue I have had over the last few years. We will have to wait and see how this winter pans out.

Regarding the NC valves I quite like that idea and then a single anti freeze valve on the lowest part (which is the return pipe). Would ordinary motorized zone valves work for that? My pressure within the system is about 0.8 bar.

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bontwoody

(@bontwoody)

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Joined: 4 years ago

Posts: 934

05/11/2025 5:29 pm

Its what ive used. I know some people choose ones which dont constrict the pipework too much but mine are just honeywell.

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60

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