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Someone has just raised something I haven’t come across so far - do we need antifreeze in our ufh?

That's odd. It's visible to me in both my post and where you quoted it in your reply.

I would like an effective zero disruption install. I think I could use a 9kw Grant Heat Pump costing 3.3k inc VAT run the cabling and pipework myself and even position the unit (total cost about 5k?) so it would just need someone to connect the electricals at the meter end, sign off on everything, inform the DNO, confirm it meets the BUS requirements and whatever else in order to get the BUS grant. Even without this would seem cheaper than the 6k after BUS that I have been quoted. Thoughts?

Really useful thanks @jack. I took a quick look at the Panasonic unit and on the face of it the specs look good and folks seem to have been able to integrate fully to HA using ESP32. Annoyingly the image seems to have a problem and won't load 😞

Don't forget, if you have an EV charger fitted, you also need an SPD under current regulations. To be honest SPD are so cheap these days I don't know why they are fitted as standard with a new installation anyway.

They are mandated for all new builds because at some point everyone will be driving electric. They are rapidly becoming the norm. When you build a house you have to comply with the rules for those coming after you. For the same reason, if you update the house electrics (add a circuit or whatever) you have to comply with modern regulations and update other parts of the system as required by the latest rules at the time of installation. Other wise we'd all be still on rewirable fuses. "They work well enough, and are cheap, why should I have to change..." Etc, etc, etc 🙂 If it is still possible to specify a 'dumb' charger I'd do it while you still can. From long experience with electronics, the more basic it is, the longer it will last. Avoid anything that needs a WiFi signal to operate because it will become obsolescent before you blink

This may be helpful, but I think that the bottom line is that anything other than the current marginal pricing scheme is lilkely to be gamed and hides true costs. https://www.carbonbrief.org/qa-how-the-uk-government-aims-to-break-link-between-gas-and-electricity-prices/

Thank you both markc and Mr Punter. Was thinking of getting ready made dry screed delivered to the property. From estimated I got over a year ago if memory serves me right I think cost of was in the region of £400 - £450 for the dry screed. Would imagine wet screed is going to be more expensive but I will be saviung on labour costs. Regarding the dry screed , delivery will most likely be dumped at the front of the prooperty. How do I make sure it consistently stays moist of enough for installation? Keeping adding every so often and mixing it

Fitted already.

it would be nice to see a comprehensive reasoned breakdown of alternatives to the status quo. Any suggestions for sources? Or we could all make our own armchair suggestions on here and start another shouting match... 🙂

It's a valid point Nick, I suppose there could be some short term variation room by room and, perhaps more so floor by floor with insulation between floors having an effect, but I guess overall the temps will balance fairly quickly with flow round the house via the mvhr anyway.

Eh How does one size the thermal emitters without knowing what they need to cope with. May as well go back to an open fire on an outside wall if RbR is of no relevance.

Thanks Simon. I've not had any contact with Panasonic, I've left that up to the person who doing the install - he seems to be struggling with a fan coil system design, initially it was a spec for the ducting but now seems the more complex issue of whole design for pressure drops etc if we went for a multi room fancoil. I think we've almost ditched that option now as seems far too complex to sort out so, looking to do individual fcu in each room instead, obv more pipework needed but I guess it's swings and roundabouts compared to the multiroom option.

Room by room is a bit pointless, imo, as the house will just do all it can to equalise the temps throughout. Add MVHR in to the mix and it becomes even less important.

This sounds sensible, thanks JohnMo. The ashp will be set up for wc and we're going with a single zone for ufh in the gf. Not sure about the ff/sf though, the Aquarea allows 2 zones so we could keep the bedrooms a little cooler I guess, not sure it's needed though 🤷‍♀️

I've only done the whole house calcs via Jeremy's spreadsheet. I will set to work with a room by room calc and see how the rooms compare. Our part O was fine so no issues with overheating but, we'd like the option to cool anyway.

The advice from @Russell griffiths was good. A labourer would be useful, but not if they don't know what they are doing. You may as well get them to mix (with a mixer) rather than have it delivered. Make sure is it just moist enough that it holds into a ball if you squeeze it, but not wet. You are best with a polythene layer on top of the Celotex. A laser level may be helpful. A long aluminium straight edge to screed with. Use kneepads. I wouldn't fancy doing this myself as I would be too knackered after the 2nd hour.

Dry screeding is DIY able if you get yourself organised first … or it can go horribly wrong. At 50mm thick, 21sq will be around 2100kgs so you are looking at 3200kgs (ish) - a lot to move for 1 or even 2 people. levels / flatness are your next concern. Set out your finished level around the perimeter.. small blocks screwed to wall work well. You can then use a long spirit level as a screed bar and work from your level blocks. get the screed mix into place and compact it well by walking around and/or an electric compactor. When it’s upto (slightly high) level, scrape it back to level and flat from the level blocks. ….. or just use wet screed and save a lot of effort.

Insane

The depth of 250mm is because i have to make up around 325mm-350mm ground to get to sub floor level. Using 250mm seems like a good way to this and bump up the ground insulation. I think we're now pretty set on going the foam glass route because it also seems simpler build wise.

I need to dry screed the an area of 21 square metres of what is to become kitchen in a newly built extension, depth about 70 or 75mm. About to lay Cellotex insulation followed by UFH and then screed to finish of. Have never done it before but watched plenty of you tube videos. Was thinking of hiring a labourer to help with install. Can hire 2 labourers if required. Any tips/advice, is it a DIY job. Off course most crucial thing is to get a perfectly level floor.

Was pretty much ruled out. All mandatory options have now been ruled out, not just pay-as-bid. Decisive Government in action / Decisive Government inaction. What you think the market will bear (for each half hour slot), knowing that if you bid too high, you'll get nothing.

Option 1 is the way to go for old building with solid walls. RFG acts as a capillary break and also acts as hardcore and yes will need to be compacted. You have to wrap the RFG in a geotextile membrane. Have a look at Mike Wye and Unity Lime for drawings and detail. Out of interest you have mentioned 250mm RFG depth- is this to achieve a certain U-Value or something else. Of quoted figures for RGP depth is about 175-200mm.

Hi, there's a lot of different sands available, as with the lime, but I'm trying to avoid a couple of scarcely used big bags of material sitting and going off!

Hi Roger, thanks for the reply - but I'm not sure what the 'it' refers to!! Geoff