JohnMo

Are people over thinking things or an I missing something. You should be controlling the internal RH to 60% max, regardless of the ventilation system installed. It really doesn't matter too much what temperature you have the house at, you still control at a max of 60% RH. I just have auto boost set to 55% to keep me away from 60%. So you just plug in 60%? You keep you house at a min 16, but more likely 19 to 21 Deg.

I went ICF. It's more like a Larson strut, a structural frame (95x45) filled with insulation, then 50mm PIR glued to the structural frame, then a non structural frame 75x45,filled with insulation and a further layer of PIR. Replace outer layer of osb with cement board.

That wasn't what we did in the end, but it gives a 0.1 U value

Bonkers the difference in price, that's why I went DIY. A friend helped out, I insisted he got paid for all hours worked, so it was a job and we worked an 8 hour day Mon-Fri. He worked as a pair of hands and we bounced ideas of each other. Took about 4 weeks to build all external walls (70m x 3m).

Buying a kit of parts with manpower to erect isn't a cheap option, I fell over at the prices. Then did something different. Or better if you want. Good insulation and airtightness does have to cost, it's all about the details. I have sold 10 houses over the years and every buyer has asked, what we pay for gas and electricity, they may not know or care about the details, but running costs is a factor. You are building for yourself - no one else, don't fool yourself (unless your a full time builder) otherwise you would just buy a bog standard house. I have lived in new, old and very old houses, and nothing comes close to what we built. Looks better, feels better (MVHR and UFH) no drafts, great views etc. Do it well, otherwise you won't see the benefits, and you will sell and move on. As way of an example just looked back at our old house, its August gas bill had more kWh of gas consumption (heating was never switched off), than this house would use in Dec. This August will be standing charge only. So in today's terms and prices August alone is £75 cheaper.

I started combi, every room Thad a thermostat and my first quarter bill was a 100% more than expected. Over a couple of years got it down to one thermostat in the house and heated on a batch basis. So heated floor once a day for 4 to 7 hours, to compensate for the boiler being too big. Got the system really efficient. But doing it again X plan every time Another read IG_The-Knowledge_PDF_Final.pdf

So your doing a biggish house, a combi to supply a couple bathrooms will be quite high kW. The problem then is the boiler really ends up too big for the heating. I have had both a big combi and a hot water cylinder. If doing gas this is what I would do a system gas boiler sized as close as you can for the heating load. To do this you need to heat loss calculation. Then plumb for hot water priority, or X plan. Under no circumstances do S or Y plan, which the plumber will want to push on you. Priority hot water allows you run hot water heating and UFH at different flow temperatures and get the best efficiency from the boiler. Add to this a heat pump unvented cylinder, this has a huge 3m2 coil and give quick recovery times. A good video to watch Don't flood the house with thermostats, instead run the boiler on weather compensation. New houses have quite low heating demands and when we split the stop much the boilers just can't cope and are likely to short cycle - use loads of gas for heat given out. Good boilers are Intergas, Atag, Vaillant and Viessmann. There are others but no experience. Tell us more about your house, insulation levels air tightness ventilation etc Solar PV yes, solar thermal will disappoint. But all the above said you should really a do heat pump. Heat pump £2500, cylinder £1000, not much other costs, run the UFH direct from heat pump, 3 port valve to either cylinder or UFH.

We have a big wall fully glazed its triple glazed, it blocks out most noise, but strangely you can hear birds.

Is this 3 phase? https://www.tradesparky.com/solarsparky/accessories/miscellaneous/growatt-groboost-hot-water-diverter?affiliate=product_feed&utm_source=product_feed&utm_medium=product_feed&utm_campaign=product_feed&gad_source=1&gclid=CjwKCAjwjqWzBhAqEiwAQmtgT4NybsNmb99vZxGAhTc2mgxifbz38oME_ZzdKHxk_z65l8binR9gvhoCGFYQAvD_BwE

It's been discussed before, Would be worth doing a sanity check on the maths

I don't let mine do that, it's available to heat from midday to midnight. Found that work fine. I also have a diverter to immersion. If it's sunny ASHP doesn't come on. But keep it simple, you won't be popular if you mess up. I would keep ASHP set as is, possibly change the times. You have a battery use a cheap immersion timer to switch on immersion at asset time. Or set up some logic - if PV generation is x_kWh and battery is above x% switch on immersion for 30mins, repeat (no idea how you do that but it's been mentioned before).

This video at about 12 minutes in says 5% uplift as TBOE, just the same as @SimonD - just beat me. https://youtu.be/OzSEQ77t20I?si=RX9qyHswllF3Q9cx

This post has the details on enthalpy and not enthalpy MVHR In your case perhaps enthalpy may be the way to go

But does it mean you have to? No

Or a simple mixer on the cylinder outlet, mix in return flow to out flow to produce a fixed flow temp and use a simple thermostat to start or stop circulation pump. Same as you would do for UFH.

If short on space, a small cylinder with a couple of immersion heaters a 90L is only 650mm high and £350.

But it's still a rebadged sunamp. Possibly higher price also.

Because the material in the sunamp requires a minimum in flow temperature. Basically you have a change phase from solid to liquid and the keep heating. So if the melt temp is 55, all the energy has to be added at 55 or above. Anything below that does not add energy. A water cylinder adds useful heat in a different way as they do not rely on a phase change in the storage material.

Last week there was a thread and @ProDave and I listed our current and past humidity levels. Dave is North or West of Inverness in the Highlands and I am East of Inverness possibly 70 miles between us but different climates (we are not so extreme cold and if it is cold it's a shorter period). Enthalpy is good for long cold spells and keeps the humidity to sensible levels. We had a week at or around -9 and the humidity stayed sensibly, but we didn't bother with a MVHR pre heater, so the MVHR is possibly in self protection mode (although no lights came to say that). I would say if your not in a cold spot in the Highlands of Scotland, or need a higher humidity level for health reasons, the benefits of enthalpy heat exchanger are low, and also you possibly don't need a pre heater at all in the UK at all.

Not sure what you are trying to get towards with all the data. But currently outside it's 8 degs and 74% humidity. House inside (MVHR) it's 19 degs and 48.5%. No heating on. The summer house also has the heating off its 11.6 degs and 54% humidity (dMEV).

Didn't notice, so must be. Also looked at our summer house with dMEV and that dropped to 32.5% humidity on the same day, the weather at that time had been a steady 3 days of sub zero temperature. From the sleep foundation According to the Environmental Protection Agency, the best indoor relative humidity falls between 30% and 50%, and it should never exceed 60%. Other studies suggest 40% to 60% is a better range. So at all times stayed within the recommended levels, most the time it's at 40 to 45 range, mid May we got up to about 55 to 58% but was hot and had cooling on and most likely the windows and door open after. So no concerns, always in the recommended range.

You do need a ventilation strategy however. It's great getting rid of drafts, but you do need to allow in and out in a controlled manner, for a healthy environment.

Our last house was in a conservation area, the previous owner had double glazing installed under a grant by the council and they were uPVC. Would not be my choice. The ground floor still had the original (200 year old) wooden windows which we had refurbished. Had never heard of this until I came on here, have only bought and sold 10 houses, and the subject has never come up. The rest as @ETC says

@RobLe stated one reason for h environmental plus a safety issue, flammability. Reasonable write here. Note we are a moderate climate not a cold one https://sprsunheatpump.com/Differences-between-R290-and-R32-Heat-Pumps-id46798837.html

Was looking through some old drawings for our house and one iterations was timber frame 1.1 U value, build was Change the osb for cement board. And build fire resistance outwards.