JohnMo

But do you really get that many days at -3, compared to days at 7 to 10 degs.

Maybe, but most houses on here are outside their comfort zone, ventilation heat loss just too small, to allow s tick the normal tick box. Hence plenty are specified way over sized.

Use a normal domestic one, your just heating a buffer as far as it's concerned. Depending on hot tub size a big one. To keep the ASHP inhibited and pressurised you may need to plate load the hot tub, but size the phe correctly, you have a 2 Deg approach temp. Then you have no issues with DHW heating, it just switches the diverter valve as normal. Add a second zone for cooling, so it bypasses the hot tub or have the hot tub cooler in summer and as cooling buffer. Heat pump doesn't care if it doing heating or cooling it just moving the refrigerant 4 port valve to a different position (as long manufacturer hasn't disabled the cooling function). Most heat pumps have the functionality to have different zones as cooling only, heat only or both. And the functions can be independently set for each zone.

I just looked and came to same conclusion you did, even NE Scotland I can have in two days.

Have you considered using a single heat pump? Size the spa heat pump big enough for the house, use the volume of the hot tub as a heat source for the house via a plate heat exchanger and mixer valve. Heat pump does two jobs, keeps hot tub temp stable, and or DHW via a diverter valve.

Read the data sheet for the heat pump in the offer to make sure it is doing the correct output for your heat loss. The nameplate sizing as with most manufacturers is not very well representative. And make sure you are being pushed into a buffer when you most likely do not need one. Also don't go pre-plumbed cylinder. Lots of stuff on apre plumbed you pay for but may never use.

Norway isn't in it - fully And we aren't so could do it tomorrow if we wanted

They have rules about country made content, something like 70 to 80% of material content of engineered products have to include, materials and manufactured content made in country, otherwise they get with huge import tariffs or no permission to go ahead with the project. Then cost of manpower doesn't matter then, people are employed government gets income tax etc. Why the heck we don't have such rules is bonkers.

Well done

To put that into reality that is double a passivhaus. Really look at how they have accounted for ventilation heat losses. With MVHR ventilation heat loss drops from big to negligible. Another thing we are 192m² living space plus another 26m² in the insulated space. Our roof area is around 50% more than yours as is our floor area, as we are single storey and every room has vaulted ceilings. All of which (part of form factor) really add to our heat loss per m². We are nearer 13W per m². With a 12kW you may need a volumiser, depending on water volume. You can always get a volumiser with immersion that gives you another 3kW if you really need it. We have an oversized heat pump that doesn't modulate well. I can get acceptable SCoP from it, around 4, if it modulated better I would be getting closed to 5. So a 25% reduction in running costs. So sizing is important. Looking at heat pump monitor a 12kW appears to modulate down to about 4.5kW, cannot see any 16kW on there.

And should be scrapped as well as the wearers of the crown and all the hangers on. But that's a different conversation.

So if that's heated - have you accounted for the net input this provides to the building. If the space has insulated external walls, the heat in this area is added to the building internals.

So how are you heating all of that,is that included as well in heat pump sizing? Depending on how you have calculated ventilation losses there can be plenty of room for error both ways. Is your thermal bridging any worse than the glazing U value? If not impacts aren't much worse than the glazing? If the steel is insulated on the inside most likely not a huge issue.

Even at 490m² at -3 your figures sound high. You possibly have better U values to me, your form factor will definable better than ours. So unless one side of the house is all glass, 9kW maybe a little high. At around 200m² we are 3kW. So 2.5 x 3 is 7.5kW, nudging 8kW (including DHW) at -3. So if Panasonic do a 9kW, I would be looking at that with some wiggle room. The bigger you go the bigger the pipes, flow rates to accommodate etc. So definitely wouldn't be looking at 16kW. But you will build houses big - are you actually going to use all of it? If not why not 2x smaller heat pumps in cascade. Then you can modulate down to 2kW and all the way up to 12kW+ should you need it.

One good thing about plenty of wind power is it's CO2 free. Our current CO2 intensity