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 unsure if this would work as had read about pumps in series but I reckoned that with the 10mm microbore pipe and the UFH being 60square metres in total a single pump wouldn't manage. All these pumps are linked to the main Salus pump which is controlled via the ASHP so all come on and off together. And it all seems to be working OK.

The DHW is now seperate as I decided that it would be more efficient for the ASHP to purely do the heating, also I couldn't figure out how to set up the controls for DHW. So DHW is now heated by an immersion heater but I have had an Iboost fitted this year as I have 10 solar panels as well and so for the whole of summer that heated all the hot water we needed and now as I am on Octopus EV tariff I pay 7p a KW to heat the water at night. I have it on for 1 hour so a maximum of 21p for loads of hot water at 60 degrees so far hotter than the ASHP would heat to.

And  that is essentially it, the instructions for the unit are useless and all I can do is switch it on via a timer or have it on all the time. But that is not a problem as I now plan to run it just for 12 hours at night in this shoulder season when it is quite mild through the day and when it starts getting much colder will have it on all the time. It is set to 30 degrees return temperature so that the flow temperature is about 34 and it seems to quite happily modulate up and down as necessary. It does not seem to cycle much, if at all. I will have to keep an eye on things when it gets much colder  and see if I need to increase the return and therefore flow temperature at all. It uses about 1

KWH of electric but for a big 5 bedded house I think that is reasonable and the house is 20 degrees at present so the wife is happy.

I will try to post a couple of pictures but may have to get the wife to help me do that.

Total cost has been about £1,000.