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Nice. Those sofas are a definite improvement and nice idea with the recliner/window combo. That large fixed window with side door is an arrangement I'm thinking about. How do you find it? Seems like it could have been mirrored at the kitchen end but see you went for a slider + french doors. What were your reasons behind that?

And that is the sort of layout I was thinking about. I've seen designers recommend this approach and it does look nice. In this case maybe a couple of chairs replacing the sofa backing the dining table. But some sort of room divider appeals more to me. Do you have any before/after photos? If you don't mind sharing.

Nice design. Has many elements that I've been thinking about for my future project (if it happens) so taken some ideas from it. One hopefully very minor thing. I think there might be a mistake in the drawing that you might want to look into. I see on the drawing that space for downpipes has been allowed from the upper bathrooms except for the guest bedroom. There is also a downpipe leading to nowhere on the floor above in the corner of the kitchen. I'm guessing the layout was flipped at some point and this wasn't moved? Depending on your construction this might be a very minor detail or a real pain to fix if not addressed before foundations are done. The space between kitchen island and dining table seems very large. Are you planning on some form of room divider there?

Ah sorry, and now I look I see you did in fact mention them!

Excellent progress as usual. Hope you mend quickly! You don't really show it (maybe the start) or mention it but I presume those external MHVR ducts were heavily and carefully insulated before being boxed in?

Indeed. Depends a lot on what you have. Just to note, I'm not particularly knowledgeable about this so just repeating things I've seen written here by others. Common improvements over last 30 years: 1. Low E glass coatings etc 2. Argon filling vs plain air 3. Larger gap between panes 4. Better insulated spacer bars 5. Better frames (especially if you you look at the older metal frames but UPVC too) and probably more Suspect so, especially if they are small windows and seem well sealed.

Can you do something like this (red line):

75oC is wrong for a new system. A lot of existing systems run like that which I guess is why they use it (though when I just tried it it defaulted to 70). Either way if you are designing for efficiency, the lower the better. IIRC @marshian's system runs at something like 35. This does mean you need to specify bigger radiators. I think this sounds a little high, checking out their tool it doesn't ask how much insulation you have or how good the double glazing is for example. So they are going to assume for an average property, which as you are in the process of upgrading yours probably won't be. New double glazing is a lot better than 20 year old. A single skin wall with 50mm PIR on top better than an uninstulated cavity wall and likely better than a lot of older insulated cavity walls. I think it's worth trying out some other calculators to see how things line up. Jeremy's one mentioned above is here but it's less user friendly than others: Others here are better to ask as I've been more focussed on new build than renovation but you didn't mention anything about the floor. If you have a wooden ground floor which is ventilated then insulating that and especially putting in an air barrier to stop the air from the ventilated space exchanging with your warm air from the room is something to look at. To be clear, you don't want to block the air bricks, you want to stop the air moving from below the floorboards to above. You mention adding insulation to single skin walls, but not to other external walls, there might be scope to beef up insulation in other areas (though sounds like you might be a bit past that point now). Edit to add: if you have fireplaces/chimneys thats an area to think about. If you are maintaining the use of a fire then unless you are using a completely sealed unit you will need to maintain airflow into the room to provide air for the fire (which is a problem if you want to air seal), and if you are air sealing you also need to think about maintaining enough ventilation to stop problems with humidity/stale air.

Something to bear in mind. A lot of discussion on this forum related to heating is based around trying to build the most efficient systems an for most situations that is to run heating systems "low and slow", ie, at a low water temperature continuously, rather than the traditional UK approach of only putting the heating on for relatively short periods (morning and evening) and letting the house cool down at other times. If you have a very uninsulated house then the low and slow approach will possibly consume more energy but for any house with reasonable insulation/airtightness (nothing cutting edge) then the low and slow approach will be much more efficient and comfortable* but it feels 'wrong' to many people who think it will cost a lot more to have the heating on continuously. A benefit of designing any system for the low and slow approach is that this is the best approach for heatpumps and a swap to a heatpump at a future point should be fairly simple. For a low and slow approach, even a big house will likely be fine with a small boiler, but if you are really attached to the traditional burst heating approach where you put out a lot of heat in a short period of time more might be needed. As you are doing a refurb, if you haven't put much effort into the insulation/air-tightness yet, now is the time to do it. * It results in the structure of the building warming up which can reduce dampness/humidity issues (though ventilation required as always), avoids big temperature gradients (feet colder than head), etc.

That looks like quite a large area. Might be worth paying someone who has the right equipment to come and do it. Be done in an hour or two if they have a small tractor/skidsteer with the right attachment.

Nick's suggestion should work. It's a very cheap thing to do (<£10) so why not try it and come back if it doesn't work? You just need to stop warm air touching cold surfaces.

My comment was based on your moving from an insulated raft to either an uninsulated one or traditional foundations. If you always were on traditional foundations with the slabs just as a floor surface then sure. Is that the case? If that is the case, then am I right in thinking that you wouldn't have had a completely flat and open space for the concrete guys to do the slab? ie, they'd have to work in room shaped areas with lots of corners? That's bound to have put them off if so.

I haven't watched it all myself but the early bit covers most of it. Maybe ~8min - 18mins in. Watch at 2x speed to save time (though that takes a bit of getting used to

Below is a video with a discussion on this with Hager talking about how they worked with Valliant (at their request) to build something specifically for their heatpumps.

That is my understanding. If the cable is otherwise protected its fine, but at least on retrofit installs doing so may be tricky. Only if to the right spec, hence need to follow the manufacturer. As an aside, either I'm missing something or it feels like the regs are calling out heatpumps, etc, but ignoring a whole load of other devices that could be as problematic or more. I suppose BIG heatpumps could be more of a risk but smaller heatpumps aren't drawing much different power from many other home devices these days that will also have issues with high frequency leakage. Induction hobs, computer power supplies (which can be 1kw+ on gaming PCs) and high power battery chargers. All of which will work at freqencies far higher than the 20khz spec that Valliant is talking about. The trend is faster and faster switching speeds, cutting edge stuff will be working at 1Mhz+.