SteamyTea

Do you know how much you use at the moment? If not, find out, it will help no end and take most of the guess work away. There may be a condensation problem if the PIR restricts vapour transmission too much. Have you considered Air to Air Heat Pump/s. Depending on the house layout they may be the cheapest option for space heating, and as they do not get RHI, it takes the time pressure off you. They get a better CoP than a wet system. You say you use little DHW, but have you thought of using a PV diverter to the cylinder to optimise self generation usage?

Regarding the DNO refusing permission to connect a heat pump. They are not stupid, they know that nearly all ASHPs are inverter driven, and that customers will quote the maximum thermal energy output. Because of this confusion they can legitimately claim that a local upgrade is needed, an upgrade that probable needs doing anyway, but at the customers expense, rather than their own. Call them up and say you know what they are up to, give them the model spec and I am sure they will let you connect it. These, as Susie says, are just immersion heaters. They have the advantage of being cheap and easy to install. You may be able to use them in a similar manner, in conjunction with your concrete slab, as a storage heater on E7. Just a case of running the numbers and seeing what comes out. The thing is with a wet UFH system is that it really needs to be put in the slab, hard to do after the slab is poured. You do need a decent amount of properly installed, insulation under that slab, you don't want to heat the ground under your house. A very expensive way to store DHW, but they are relatively small for the energy they do store. There is also a question mark of their reliability and longevity. I like the technology behind them, but seems excessive to store a few kWh of thermal energy. And you will need a water softener if you are in a harder water area (not a problem in Cornwall, well not my granity end anyway).

If you can add it now, you should. You can calculate how bad the cold bridging will be. White Pine has an across the grain conductivity of 0.12 W.m-1.K-1. PIR is around 0.03 12 W.m-1.K-1. Convert to the thickness dependant R-Value, along with the rest of the wall construction ( thickness divided by conductivity), add the all up, then convert to the U-Value (1/R). Don't for get the roof. You may find that is easier to do as well. And you have 50m2 of that. Be nice if he could fit an energy meter at the same time. Then you can see how much you are using. https://www.manomano.co.uk/energy-monitors-2271

Thank you

Good, or not. If it had been, would just say demolition and rebuild. Have you considered re-roofing? May work out easier and cheaper, and you can add in PV if suitable.

No. But the Met Office will have some data from your nearest weather station. https://www.metoffice.gov.uk/research/climate/maps-and-data/historic-station-data It is really the distribution you are after, not the mean value.

Is your place a Cornish Unit?

Was at school with someone called Flint. Got expelled for cheating in his 'O' Levels.

@AliG There is lots of info on how i is calculated on the Ofgem site. https://www.ofgem.gov.uk/information-consumers/energy-advice-households/check-if-energy-price-cap-affects-you

Or buy some of these

You still got that spreadsheet and are you willing to share it?

That seems quite high to me. My daytime usage is sub 15 kWh a week. That would only go up slightly if there were more people in house.

If you never want to see Wendy again, @pocster will show them off in person.

Don't think I am. I am on a variable standard rate. May just check again. Every time I have looked into swapping, the most I have been able to save us £9/year. I am not going to bother for that. I am a low user on E7, 80% of my usage is at 14p.

I did.

Not sure what "all the numbers" are. Assuming power then multiply by the correction factor.

What I pay for EDFs day rate.

That will be the Lizard then. Can you change the roof to a warm roof?

Yes. Don't need much as it disperses quite a but when mixing. Pretty sure it is already used on thin floors. https://concretecountertopinstitute.com/free-training/introduction-to-gfrc-glass-fiber-reinforced-concrete/

Can you isolate it, loosen the joints, swivel down and remove?

Yes, no need to teach the craft people how to measure and add up. I had to teach IT on the plumbing course. Monday afternoon, in the room next to the sports field. Monday afternoon was when the girl's football team practiced.

I went to Jeremy's not long before he moved in. I was amazed how quiet and non echoy it was.

How much does your car take in a usual week?

Thought of that, but my day usage is less than 2 kWh, 50p a day.

Photographs may help.