Commencing on an ASHP Installation Process

Sheriff Fatman · 2025-04-20T22:02:59Z

Hi AllI've posted a general intro post in the introduction section, but the main reason for joining the forum was due to our commencing an ASHP quotation process, for which I can hopefully gain some insight from other forum members.Our combi gas boiler is still working, but on its way out, so a ASHP seems a logical decision alongside our existing solar PV and battery system. To date, I've done several standard online quotes, all of which are landing in pretty much the same place (£6.5k-$7.5k, after the BUS grant). There's been one exception to this, which was Boxt quoting a fixed price of £4,599 after the grant, but with a downside that you have to pay the full amount upfront prior to any sort of survey taking place, which I'm very wary of.Our property didn't have a current EPC, so we've paid Octopus (our existing energy supplier) the refundable £200 deposit for a combined EPC and heat pump survey, which was carried out last week. It was very detailed, taking 4 hours to complete, and we now have an updated quote from them for an 11kW Daikin heat pump with 9 radiator changes out of 13 in the house. The main complication from the survey was the conservatory at the back of the house which accounts for 1/3 of the total heat loss in the property. However, there are two large radiators in there which the calculations showed recovered 97% of this, meaning that the installation fell within scope for Octopus.From an installation perspective, the surveyor seemed to think it was a fairly straightforward installation to carry out, as there are no planning permission or structural survey issues, and the heat pump can be situated on a gable wall, with pipework going straight up into the loft and across to an existing airing cupboard where the old water tank used to be situation prior to the combi boiler being installed in 2014. Consequently, I now have a much better base level of information to work from to be able to compare alternatives.So far, I have arranged for an on-site visit from Aira this Friday (90 minutes, so less detailed than the Octopus survey). I've watched a few videos regarding them but, having read the thread on them on this site today I'm not sure I want the 'install and forget' kind of system that they provide, as I'd like to be able to tinker around with settings to optimise how the system works, but I'll see what they come up with.I've read a couple of posts on here from people who've used Boxt, and will read up further on them. There's very little available on YouTube in the way of customer testimonies. If I can get myself comfortable that they're going to spec a reliable system and do a professional installation then their pricing is difficult to ignore, particularly as it's based on a Vaillant heat pump which seems to be well regarded generally, and is probably one I'd prefer to have than a Daikin unit. Their quote covers up to 6 radiator changes, so if 9 were required this would add £360 to the cost, based on email correspondence I've had with them. The big question mark currently is that the standard online quote has specced a 7kW heat pump, which I'm now concerned will be undersized based on the findings of the Octopus survey (which ruled out their own Cosy units as an option as there isn't one big enough currently). I'd love to get them to complete a survey to confirm their findings and pricing, but am holding off on this currently due to the capital outlay required (which I've been assured is refundable, less a £150 survey deduction, if I didn't go ahead).I've had other standard quotes from E.ON and EDF, both of which I think are also speccing Vaillant systems, but at a higher cost than BOXT. I've not done anything to progress these further at this stage, but the pricing of both is very similar to Octopus.We have a bit of time available before having to make a decision, as our eldest daughter is about to start her GCSE's, so I wouldn't want to commence a disruptive installation process while she's doing these, which means that the end of June is the earliest installation we'd be looking at.If anyone has any particular insight they'd like to share, then I'd be grateful, particularly with regard to their experiences using BOXT, and also if anyone has any recommendations for other potential installers around the Leeds area that might also be worth considering within the process. We used a smaller, local installer for our PV and Battery installation and they've been fantastic both at setup, and in their aftersales service, where a couple of optimisers have had to be replaced under warranty. Consequently, even though the quotations to date have all been from 'big names' with the exception of Aira, I'm not averse to using an independent company based on word of mouth recommendation, provided that they are suitably certified. To date, it's been harder to identify any via the usual search processes, other than via using one of the advertised 'search sites' such as Greenmatch, who's T...

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Air Source Heat Pumps (ASHPs)

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JamesPa

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23/05/2025 2:46 pm

Posted by: @sheriff-fatman

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Posted by: @jamespa

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What value of air changes per hour is assumed?

It varies by room, but the conservatory is assumed at 2 per hour, as is the kitchen, hallway and landing.

Living room and upstairs office are assumed at 1.5, bedrooms at 1, and bathroom/toilets at 3.

Two calculations both use similar figures, with the exception that one of them assumes 2 for the ensuite and downstairs toilet, rather than 3, so I assume they have some sort of common reference point to estimate this.

One of the calculations excludes the conservatory, so I only have one calculation showing a figure for this. Within my replicated spreadsheet I can manipulate the figure and each additional digit adds about 400W to the conservatory ventilation heat loss.

I think those are pretty much the standard figures that used to be quoted in mis3005-d (which now instead references a BS EN standard that I have yet to read)

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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