-rick-

https://barkeepersfriend.com/

DHW definitely the limiting factor, depends how you design your system whether it's an issue. If the tank is big enough to handle the morning (or evening) routine in one hit with room to spare then reheat even if long shouldn't matter too much, just comes down to scheduling. If heat loss is 2.8kw, a 4kw unit can spend several hours a day on hot water (not all at once) and still have capacity to heat the house. This depends a lot on the heatpump though doesn't it? @JohnMo was talking about how his new 4kw heatpump had a much bigger external heat exchanger/radiator which should lead to a lot less icing/defrosting than his previous 6kw (downrated 9kw?) unit.

If these use the same internals then it's likely the minimum modulation is the same on both. If that's true then there is no benefit for going with the smaller model. Which means with a max heat loss of 2.8kw and a 7kw heatpump you will likely see a lot of cycling which is not great for efficiency. I feel like I'm channelling @JohnMo, surprised he hasn't spoken up yet.

Neither? Even 5kw sounds a bit big. Smaller heatpumps are available, Important to get one that can moderate it's output down a lot. Most of the year you'll need a lot less than 2.8kw

Any thought given to putting in a continuous layer of the 150mm eps then putting the pipe with PIR insulation around/40mm? on top (foamed in)

and I'm not stopping... This is stuff you have actucally bought and checked is 13mm? I ask, because the photo shows a pipe with insulation that looks thinner than the inner diameter of the tube. 16mm tube, 12mm inner diameter. Edit: Basically the photo looks identical to the ones advertising pipes with 7mm

Agree, not how I look at it but I think most people think about touch points, so expensive fixtures and fittings that feel luxury (eg solid metal rather than plastic and name brand 'premium' appliances, etc.

My reading was lots of insulation on top of the duct, none below. I assume there would be free air in the duct also. Edit: and the MLCP stuff I was looking at was 7mm insulation. Not sure I saw any when I was looking with 13mm. Link please?

I think what they are getting at is that plastic pipes have some minimal insulative value compared to copper pipes. Nick was talking in another thread how condensation doesn't tend to form on uninsulated plastic pipes. But that by no means they are insulated. If you are putting these pipes on an uninsulated ground bearing slab then putting some decent insulation on them seems very sensible to me. Someone here warned me off the pre-insulated MLCP pipes as the insulation isn't very thick. So fine for some uses but not if you want a lot of insulation.

I read your post as suggesting a solution to @Dunc I can see that happening over a long period of time and I'd guess the glazing industry has data on this. But I very much doubt it's relevant on the timescales discussed in this thread.

That's not replacing the argon + seal. So even if it clears the view the window is still performing far worse than designed.

How many of you are living there now? Is this a case where they are designing to be plenty for a fully occupied house but most houses are occupied a fair bit below their theoretical maximum. I'd guess flats are often occupied much closer to their theorectical maximum given house sharing and property costs in cities. So maybe there have been some problems in those types of properties leading to a rethink.

As always depends on your situation. Short runs from the manifold? Especially if run with smaller diameter pipe (10mm copper, hep2o plastic, etc), don't need HRC. If you have long runs, especially of 15mm+ pipe then HRC may make sense. I can't find it right now but there was an online calculator/diagram that someone posted before that would neatly show how quickly a tap would take to warm up given length of pipe + pipe diameter. Maybe most of your sinks are close to the manifold so won't need HRC but one is a long way away and for that one you want a HRC (connected to PIR in the room so it only runs when someone is near the tap).

I don't know how your browse activity on here but if like me you use the activity view then switching it to the condensed version makes it a little better if you want to ignore things (or even just not see every update).

Congratulations. This has been a masterclass in successful self building by managing contractors! More important than that is the contractor selection, project management, etc, and I think it's you (with assist from Mrs P) that has done that so you can feel great satisfaction with how this project has gone. I'm guessing (maybe you said before) your background is in project management and if not it's an even greater achievement. When you have time and if you have the energy I and I'm sure many others on here would appreciate it if you could share as much as you can on your process for managing this project. What your average day looked like, tips and tricks, preparation, etc. I think this could be really useful for those of us with less project management experience!