SimonD

Blimey, you have been busy! I've been kicking back in the Alps on a full AI detox until about 5am this morning. Just got back to reality combined with cyberspace already - Claude and Deepseek providing their suggestions in parallel.

Yep. https://openheatloss.com. It will do all the UFH output calcs room by room based on flow/return temps, room heat loss, pipe spacing and floor covering etc. and provide floor surface temps and over temp warnings.

If you want the BUS Grant, then you have to have MCS sign off. The important thing to understand is if the 'designers' have actually calculated in the MVHR into the heat loss. Most don't as they either don't have the understanding or the tool they use doesn't use a method that deals with whole house MVHR. For example, the new 2026 CIBSE Domestic Heating Design Guide method specifically excludes whole house MVHR. So check this before making a decision on the heat pump. You can use my tool at https://openheatloss.com as this does cover the BS EN 1281 standard for whole house mvhr. 105l may be okay, but it's important to know the minimum modulation of the heat pump first. Low temp running loves lots of volume. The Panasonic wifi connection is required for the 7 year warranty on these pumps. But commissioning cannot be completed merely using remote access as proper commissioning involves a lot more than this and has to involve an onsite visit. Unfortunately proper system commissioning is often misunderstood and undervalued. To get it done right it takes time. This design has other advantages often overlooked. It has built in expansion vessel good for a system of 200l volume. It also has a backup heater available in 3 or 6kW size so if there's ever a breakdown you have backup heating for your house. Overall, using the bi-bloc unit can be neater and more space efficient than installing another monobloc with all the additional expansion vessels and controller wiring as this is also all contained within the bi-bloc unit, especially if the alternative heat pump also requires an external circulator. E.g. installing a Grant heat pump is a pia in comparison and that's an easy heat pump to install.

I just received an email linking to this blog post from Buckland timber. Relevant to this thread. https://www.bucklandtimber.co.uk/blog/how-do-different-glulam-species-adhesives-and-surface-treatments-behave-when-theyre-exposed-to-real-conditions/

There are circumstances where tapered thread fittings are not appropriate. Clearly this is one of them so follow the manufacturers instructions. I generally find Loctite 55 to be 100% reliable although surprisingly I've just done an installation where 2 of my radiator tails are seeping on pressure testing, but that's more down to unbranded rad tails with built in drain off that I needed in a hurry so took what was available off the shelf and manufacturing tolerances aren't great!

Yes it does. Here's a couple of pics from an installation I'm finishing off at the mo.

Job done: https://uk.milwaukeetool.eu/en-gb/m12-raptor-pipe-cutter-stainless-steel/m12-pcss/

Yes, and they're great. All ours came from https://www.bucklandtimber.co.uk/ They'll design and supply all junctions and fixing for you too.

Maybe, but a good MCS installer isn't just an installer, they're a system designer too. Good design takes both time and experience, especially since the OP has already mentioned hydraulic separation. That's entering a mine field. If you find a good one, that will pay dividends down the line.

How have you determined that you actually need hydraulic separation and additional pump? This is really not always needed and I'd recommend you calculate the pressure losses fully before specifying this in a design. Even if you used CCTs, you're going to suffer from distortion on the secondary circuit, even if it is variable speed pumped. E.g. right now I'm completing an installation for a customer that has a mixture of 8mm, 10mm copper and 10mm plastic throughout. Pressure loss is no problem.

I use these nowadays, far more reliable with cone fittings: https://directplumbingsupplies.com/product/bonfix-insert-brass-with-o-ring-15-mm

True on most normal 2 x 2 unless you're picky and double up 25 x 50 roof battens. But that's really why I asked the question of the OP and what's forcing the 50mm.

If you haven't battened, what is it that is forcing you to stick with a 50mm service void and not adapt it?

Try something like this: https://soundstop.co.uk/products/soundproofing-underlay-solution If you're installing a floating wood floor are similar there are also sandwiched products you can get at 12mm thickness.

I wonder where this journey's going to end up! Excellent stuff, and very entertaining & interesting. I'm currently in a quiet period with no dev going on at all, but have too much on my plate to spend any time playing, sadly.