Iceverge

Any drawings of your roof and wall interface? If it's complex then I would recommend moving your airtight layer outboard of the rafters.

Seal any air paths too with acoustic caulk.

No calling me by my real name. This is supposed to be an anonymous forum.

I'm thinking idiot resistant ( not idiot proof, that's impossible). Simple pattern to lay. Single zone. Run at a low flow temp. Would it actually make any difference to the feel of the house avoiding walls beds, kitchen cabinets etc etc.

Ok..... Having a brainwave here .......it's hurting......there's blood coming out my ears.............. Take a well insulated house with an ASHP. Lay UFH at 200mm centres Don't bother with room by room patterns. Just slap it down in a big up and down pattern or whatever. Pour 150mm of concrete over the top and then ensure no one drills more than 75mm into the concrete. And after than go to town with room layout etc. "Trim" heat the bathrooms with direct electric to make warmer if needed. Any reason this wouldn't work?

Yup, I had 26mm mlcp coming from the UVC inexplicably via a manifold to the kitchen tap. It took about a minute and 9-10 litres of water to get warm at the tap. Solved (9-10secs) and about 1l of water to do the same thing with 10mm Hep2O. I should really have put the UVC closer to the kitchen.

According to the makers. MCLP is suitable for hot ring mains where Hep isn't. It has more in common with hydraulics fittings than plumbing. Its rated for 10Bar continuous at 70deg where Hep you'd have to drop to 50deg ish to get the same rating. It's pretty achedemic in a domestic install but for a commercial setting I can see the advantage. In Ireland and UK we can't seem to get the 12mm fittings. I really like the 10mm Hep. Its like installing 3 core cable rather than pipe and for a radial system delivers hot water extremely fast, coupled with the slim inserts I'm getting 6l/min over 16m at 3Bar. That's plenty for everything except a shower/bath or jetwash kitchen tap. Failure mode in my wellwater experience is metal corrosion (copper/brass) and I love that Hep can avoid this almost entirely. I expect the stuff I put in to do 75 years +.

It's been the standard go-to in Ireland with a while for new builds I've seen. You can buy screw fittings if you don't have the compression tool. It's a very robust system. HEP2O is an easier system to install in my experience and has less restrictive fittings for flow and plenty good enough for houses. I would be happy with a multilayer system if done well though. Much more so than copper or cheaper push fit.

Don't forget physics. Meaningful energy transfer will only occur when there's enough temperature difference. A slab at 24⁰ will impart very little heat into a room at 22⁰ but a lot into a room at 15⁰. Given identical pipe spacing, on a single zone, the room with big windows or a leaky external door will extract far more energy from the UFH all by itself than the small internal room. Its not the case that a pantry will end up at 30⁰ and the hallway at 15⁰. The pantry will probably get to 22⁰ and the hallway to 20.5⁰. In a passive class house it'll all end up at 21⁰. Regardless of pipe spacing or omitting rooms or forgetting UFH and ASHP and just plugging in a cheap oil filled rad.

If you are certainly pursuing IWI . Like John says above. Wrap everything in 25mm of PIR. foam the cracks and joints. Trim and tape. It'll be adequate for your needs.

Lol, that will amusingly make the heat route downwards through the steel so it may not help retain that much heat. To be effective you will need to wrap the entire steel and wall ( inc between the joists ) in Insulation. A small bit everywhere is more useful than a lot in one place.

I've "thermally modeled" the junction....... In short the solid wall above will do such a good conducting job from inside to outside that no further heat will pass through the steel ( it's not actually creating any cold bridge) and it'll remain at indoor temperature. Unless you plan EWI or IWI ing the solid brick wall I wouldn't give it any more thought. Similar story with the posts. A thermal bridge only becomes significant when it is disproportionately worse than the surrounding materials. The posts to the ground might be in an issue if piercing an insulated raft in a passivhaus. In your case it won't make any real difference as the existing walls are uninsulated anyway.

I suspect your humiliation is extra high in the bathroom. Is the extractor fan working?

Very strange indeed but it's not entirely impossible there's a bad batch of seals or heat exchanger a floating around. It would be easy enough to set up a rig to pressurise one side of the unit and see if it leaks out. I'm thinking a couple of bungs, a Schrader valve and a bicycle pump. Pressurise the exhaust(or inlet) side and see if it leaks out immediately. Perhaps something as simple as a dab of sealant would be enough to cure it.

Self building is a bit like golf in that rather futile pursuit of perfection I suppose. Mind you I don't play golf.