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I agree with your point @Gus Potter I'm writing work packages at the moment and trying to paint as clear a picture as I'm able. I'm hoping this reduces the unknown details that cause the vendor to layer on contingency costs.

Mine is a new build. Just getting out of the ground so no plumber or sparky on site yet

@JohnMo That is so tempting, really.

I went for 21 Degrees. Other than Internorm they are the only vendor offering double weather seals on windows and doors. Unlike Internorm they also offer inward and outward opening doors. Norrsken were a close third but their doors only have single weather seals. NorDan likewise. Rational were good value but a step down in quality.

I posted my question to the FB Heat Geek group and two installers said they’d expect to charge £10-12k for the job before the BUS grant. Seems to be the going rate so at least I have some grounds to push back on my installer. He does seem to know his stuff though. I could go down the umbrella scheme route too. Where would I find such a scheme?

I admit I know nothing about the effort and additional costs involved with installing and commissioning an ASHP so bear with me if this question is stupid. For £5k (excl VAT) I can buy a Vaillant aroTherm plus 5kW and a pre-plumbed 250L cylinder. A local heating company wants £9400 to install and commission it (£6.9k after the BUS). Does that seem reasonable, allowing for a bit of profit? The ASHP will be installed outside my plant room and plumbed directly to the cylinder within the plant room and previously installed UFH, so a really simple install.

This is what UK Power Networks specified for the connection kiosk:

Thanks Nick! I was about to pay £300 more for the kiosk using a supplier proposed by UKPN. This one meets UKPN spec for my three phase 100A supply. https://www.ebay.co.uk/itm/193638966542

I'm probably doing the same. GRP kiosk with the DNO cutoff and a three phase meter. What size is your kiosk? Did you need ventilation?

I can’t afford to eat real food so I’ll have my gruel before we meet.

I apologise for hijacking this thread but couldn't find a good forum to ask. Does anyone have recommendations for a scaffolding company in our area? I've been quoted over £9k for 10 weeks of scaffolding around my build which seems steep!

That works for me. I’ll be the one obsessively clutching a roll of plans like a drowning man.

Sorry, I'm away on business that week.

I'm with you @G and J - I think I've driven my architect mad with all my revisions. I'm sure they'll have PTSD by the end of this process. Will share what he comes up with, though I hope he meant 'counterflow spiral'.

I finally found a local Heat Geek to take a look at my requirements. His feedback was: maybe use a 5kW ASHP to avoid being capped for DHW on colder days; use a design temp of -3º external and 21º internal; use a spiral pattern to avoid pressure losses caused by excessive bends. Apart from the last one, you guys called it first I'm now waiting for him to quote for me for the design and install. Feeling much more confident. Thanks!

It was all great feedback, I really appreciated it.

Regarding the slab design, this was really stressing me but I've decided to go with my SE's design. I don't want to reopen that debate, sorry.

Clay and lots of trees. 450mm ring all the way around and through the middle too.. Some might say the SE was hedging their bets.

That's a nice strategy. Will mull that over.

Sorry Nick, what is a 'UVC'?

Another great question that I just put to ChatGPT. Roughly 3.15 hours in winter. Need 10.5kWh to raise cold fill water at 5º to 50º DHW. Estimate output of Vaillant Aerotherm 3.5kW in winter is ~3.2kW with COP of 2.5-2.8. For summer this time drops to 2h40m. I think that's ok in both cases given the thermal capacity of my slab.

I'm probably mistaken but I am assuming that with 125mm of concrete above the pipe the heat will dissipate so much by the time it reaches the surface that there's no point worrying about what's above it. Great question about the upstairs heating! I've seen a lot of people say they never use their upstairs heating, and that the MVHR will help balance heat around the house. I should be pumping enough heat in as the heat load calcs from the PHPP indicate I need 11W per m2 of treated floor area, so I've just take that for the whole house and divided by the ground floor area to get ~18W per m2, or ~2kW.

Thanks @JohnMo I missed off the minus sign so my design temp should be -0.5º. This is what the PHPP uses based on my location so I didn't change it. I'm in Suffolk BTW.

Thanks Conor, that's a option for sure. I'll have battery storage too so can load shift to avoid peak rate when running the ASHP all day.

Hi all. Please critique my UFH design. Background - my house is borderline passive so has a very low calculated heating load of 2kW for 0.5º external + 20º internal. Ground floor area is 110m2, total treated floor area is 171m2. The house superstructure is the MBC Passive frame with wall U at 0.12 and roof at 0.1. It will sit on a 175mm reinforced concrete raft set into a tray of 350mm XPS for a U value of 0.09. Air tightness of 0.6 ACH. MVHR for ventilation. Windows and doors average U of 0.85. Based on advice here and elsewhere (Heat Geek mainly) I've gone with a zone-less UFH design that treats the slab as a massive storage heater. This layout has 6 roughly equal 83m loops of 16mm Pert-Al-Pert. The loops will be placed on the lower reinforcement mesh 50mm above the insulation and 125mm from the top of the slab. There is an another mesh set 50mm from the top surface but I don't want to use that for the UFH to avoid any the puncture risk from the internal stud work nails. Once the slab is up to temperature I will feed heat in low and slow using weather compensation. My current thinking is to use a Vaillant Aerotherm Plus 3.5kW ASHP with open flow UFH and no additional pumping/buffer etc. Apart from two electric towel rails upstairs I will have no other heating. Sensible? FYI, I'm still looking for someone to design this for me who knows what they are doing ... Also would welcome thoughts on a good brand/source for pipes and manifold please? There seems so many out there that it's hard to choose!