Boxt Heat Pump Installation Experience

Adrian · 2024-12-15T14:00:24Z

I’ve just had a heat pump installed by Boxt and thought I’d report my experience here, so it might be useful to others. For context, mine is a 1930s semi detached house, heavily insulated with 300mm loft insulation, 50mm internal wall insulation, Swedish double glazing and a 2010 build extension with more insulation. I got a lot of other at least initial quotes and all of them where too big resulting in mostly 8kwh machines which would have been grossly oversized. Like octopus Boxt provides an online fixed price including replacement radiators, from what I see just based on the heatpump size, £3199 for the Valliant 3.5 unit and going slightly up from there (£3599 for the 5kw unit). After getting the initial quote online I adjusted the age of the property to get the correct model (in my case 1995-2006 to get a 5kw unit and called them to check that that was ok, which it was. They did require immediate payment by credit card, so that is a little suboptimal, but my thought was that in the worse case I get the material for that price and redo the plumbing myself and the credit card payment gives some sort of protection against bankruptcy etc. The other problem I had was that the space for the hot water cylinder under the stairs was limited and with only two of us in the house, 99% of the time taking shower and me taking a very dim view on two people having a bath within twenty minutes of each other (which is what the MSC guidelines recommend), I needed a smaller 150l cylinder. Boxt was happy to accommodate me with respect to that, which was a first. They installed the Vaillant 150l slimline unit. The install started five weeks after the order and went smoothly, all performed by one plumber and the electrician spending Thursday connecting it all. Hot water was restored on Tuesday and heating on Friday. The installed equipment is: Vaillant arotherm 3.5 Vaillant 150l slimline pre-plumbed dhw cylinder anti freeze valves all the usual expansion vessels, valves etc two K2 replacement radiators, they would have done 4 if I hadn’t shuffled a couple of them around the house beforehand. 18l volumiser Here are couple of pictures for your enjoyment:

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Toodles

(@toodles)

Illustrious Member Contributor

Joined: 3 years ago

Posts: 2151

20/09/2025 11:28 am

@editor Mars! Wash your mouth out! (I think we should regard the words “Buffer Tank” as ones that require a hefty contribution to the swear box.)😉 Toodles.

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

👍

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Ashfp

(@ashfp)

New Member Member

Joined: 6 months ago

Posts: 3

20/09/2025 12:04 pm

Glad to hear another mostly positive review of BOXT, as mine is being installed by them in 3 weeks. Experience so far has been really good, they clearly have some experienced people on the boxt side doing the heat losses and general designs.

I'll do a full write up of my experience when it's completed, as I got 4 quotes/heat losses, but the summary from boxt is:

6.5kW heat loss (this is higher than it actually is)

They're fitting a 7kW arotherm+, 200L Unistor, 20L lagged volumiser, 1 additional rad + 1 replacement (I've already replaced most rads in my house)

They wanted everything open loop but I've asked for 3 bedrooms upstairs to remain on TRVs (downstairs is quite a bit larger and will remain open loop).

£4.25k

50 degree design temp at -2 (but in reality, according to my own heat loss and backed up by the heatgeek survey too, I'll be able to run it at 42 degrees at -2)

The plumber who's installing it came and did the heat loss survey (but boxt do the actual heat loss using spruce - the report was surprisingly detailed and impressive). The plumber was most definitely a traditional gas boiler installer, but he's got very good reviews on Google and seemed nice enough. His knowledge of heat pumps and low temperature systems wasn't great (and nothing compared to the heatgeek we had round), but he has fitted a few for boxt already and another company apparently. I've done that much research that I could happily fit one myself, so I've no concerns about snagging the job. He didn't really ask or look at pipe run sizing (probably just fed back that all rads are in 15mm copper), but I'd already been under the floors and checked where we have 22mm copper and done the calcs (thanks to heatgeek website/videos) on whether we have enough capacity.

I've had about 10 emails back and forth with boxt to iron out technical questions and get specifics on the installation (pipework sizes, runs, insulation (primary Pro) etc) and they've been able to answer alebe) everything.

Like I said, I'll do a full write up in a couple of months on the full process and how the install goes.

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Andrew J H

(@andrew-j-h)

Active Member Member

Joined: 3 weeks ago

Posts: 6

21/09/2025 1:00 am

@ashfp Mine does have a buffer tank. That was my experience that they have a contractor who does not do the detailed design of the system but liaises with a contact at Boxt who does the detailed heat loss calculations etc. My report I also found was quite detailed with calculations of individual radiator output relative to heat loss of each room.

I understand that the larger 7kw Vaillant might be slightly more efficient for the hot water heating (as a larger heat pump is generally better for water heating)

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