-rick-

Alternatively the switch might just leak a bit of current even though its off. Measure the resistance of the switch in both on and off states with nothing else connected.

Have you got this switch connected via a relatively long wire? (Significantly more than the shelly was designed for - which I think is very short wires) Wire is probably picking up small current from somewhere thats not enough to change the shellys state but enough to hold the switch high once triggered (at least for a time - if you wait long enough it might reset). If a resistor works then you can play with the wiring and see if you can fix it.

If it's an active-high circuit. ie, when voltage is present home assistant reads 'on' then wouldn't a pull-down resistor be needed? ie, there is some stray signal pulling the signal up which you want to override. Would have thought a 10k resistor would be a better starting point than 1M

A dry shake floor is something I'm very curious about for if I ever get the chance to build. During your research did you look at https://concria.com/ ? They seem to be selling their solution as quicker/easier to lay and a more reliable outcome. Recently Sika bought a big share so there must be something there. Curious on any thoughts/detail you can share. In any case please come back with the outcome when you get that far.

Oh now I'm confused. Am I thinking of someone else? I thought you had a heat gain problem in the bedrooms even during heating season so wanted the ability to cool the bedroom while the downstairs wanted heat. After I read that I looked back at some old threads and thought I read about how to do that you had to install a second zone with a big buffer tank to give the zone enough volume to avoid cycling. Have I misunderstood something?

Have you completed the details fully to come up with the number or just the basics? I don't know the app but I note that the heatpump efficiency is marked at 100% in your screenshot. In reality a good install should be 400-500%. You need the detail to be correct to get good output. I've seen many on hear saying they initally got bad numbers but once all the little details were added it came out better. SAP is still a flawed system however.

What dimensions are you working to? Is this an integrated unit or just a bespoke slot for a standalone unit? If the latter, maybe a slightly smaller unit would work with some extra trim?

The different warranty providers do sometimes have additional requirements that go beyond pure building regs. NHBC definitely does (but doesn't really deal with self-builders). LABC have a large guidance doc that should be consulted before using them for warranty. Don't know about others. They don't want you doing things that have a high history of claims, even if it is building regs compliant.

It's probably more complex than this but I thought it was mainly: 1. Solar Gain 2. The temp difference between outside and inside (same calculation as with heating) 3. The amount of air infiltration/exchange (same as with heating though might be additional focus on humidity) The solar gain is the difficult one which is why if you are mainly north facing with some east facing windows (that already have shading) you might not need to worry too much about this. If you are south facing with no shading its a huge deal.

Interesting point. I assume banking on the 30 min billing windows as a benefit to single phase (because if you aren't generating enough solar you are using grid energy anyway?).

I thought that was sorted now. Roll out started about when you were getting one and is now in full swing?

This isn't exactly correct. The grid acts as a buffer and your electricity meter counts net generation. So you can generate on 1 phase and consume on another without being charged. Assuming you have a modern smart meter. Obviously you aren't strictly directly using the energy that you generated but I doubt that matters to anyone unless you aim to be off-grid, or expect long grid outages. A reason for three phase is that it's easier to export from larger arrays as you get 3x16A automatic export allowance, and it will generally be easier to get permission to go bigger if equally split among the phases. Agree that inside a house the need for 3 phase is minimal. There are some uses (big cooking appliances) but other than that and it's not much needed. Having the flexibility to install EV chargers or power a workshop are nice though.

Modern heat pumps are inverter driven. This doesn't present an inductive load (or at least nothing like a traditional motor). They will soft start,

Ok. that should help a fair bit. Also, I noticed your main room is on a north-east alignment. Assuming thats where the windows are you should be limited in solar gain coming from the east (morning) so peak solar gain will be much more limited in time than a south facing direction. Shading will make a big difference and limiting the duration of max gain also makes a big difference. Look at the average over the worst 4-5 hours, not the peak. The floor slab should provide some buffer for peak load also.

Well since no-one else has replied. Any luck with this? I can't see it working too well as shown. BTW: that cable looks like it needs attention.