JohnMo

Maybe it's more simple 12hrs at 1500W and 34p per kWh is around £6 12hrs at 800W and 34p per kWh is around £4

Not sure that's the answer. So a thermostat is connected to the internet, and you have so many zone your boiler short cycles and you use more gas. Or is it the answer, that's what they all did?

You missed the trick, connect the thermostat electrically, but don't connect to an actuator. They think they are in control, but they aren't really. Read or heard somewhere that in the 70's house temperatures, with central heating used to be controlled in the region of 16-17 on average, last year they were in the low 20's. Been in houses where the temps are in the mid 20's they are just uncomfortable to move about in

Sorry it is for Tado as I stated. It is also true if others. As I believe you are aware

Not sure apples would be that good. But they don't say the fill material, but mentions solid. Looked at the datasheet stores 100kWh, it states the temp drop of 500 to 200 degs takes 19 days. The average heat loss being 5kWh day! Pretty huge losses. Vacuum insulated.

Here's one prepared earlier https://www.caldera.co.uk/

Would need to be careful you did make a bomb, not sure of the expansion rate, but a temp rise of 450 degs, could give a big pressure rise in a contained volume of gas.

With any WC controller you should be able to set up setbacks, where flow temp is reduced, i.e. reducing house temp. You need to careful with a lot of opentherm controllers in the UK as all they are is on/off relays. For instance to get proper operntherm control from a Tado, you need to get the European version from their website, all the rest connect to opentherm but are degraded for the UK market to on/off control. A decent boiler controller should give, weather comp, load compensation and self learning stop and start optimisation. I mine does (Atag), but you have to be careful with UFH due to the slow reaction times, but with rads you can turn it all on, almost self sets the WC curve, you set the setback times and it learns when to start flowing at at higher temp and when to flow the lowest temp.

For extracting heat, you could use an air to water heat exchanger, such as a car intercooler to allow hot air to exchange to hot water and then feed into house.

When they reopen ask them where the figure came from, possibly a cut and paste from their last quote, that wasn't deleted.

I assume you are referring to to dMEV, not MEV? As MEV is a multi room ducted unit If you are installing reversing heat recovery it is normal to install in pairs, one will suck while the other blows then they reverse direction together. Or you can get single room MVHR, which sucks and blows at the same time. Another alternative is PIV, this takes air normally from the loft and has a single supply point and basically blows air through the house. The air is also filtered. You don't need bathroom fans. Worth looking into also.

They do them also I believe

You could use Tectite push fit fittings, quick easy and look way better.

Neither contribute directly to airtightness. Both will help heat losses but not airtightness.

3 or better needs MVHR, certain Scotland it's mandatory. Better airtightness means less heat loss. Coupled with MVHR even less heat loss.

There's an app "my electric meter" that does just that

First obvious question is why do you need a nearly 40kW system boiler, unless you are heating a leaky old mansion. Size boiler to suit, not what's the biggest you can get. What is your heat loss calculation telling you kW heat loss is a your lowest temp? If you want an efficient gas boiler treat sizing it and running it the same as a heat pump. Install a heat pump cylinder with a 3m2 coil, for fast recovery and a big delta T to ensure return temps are low, for condensing. Install as DHW priority, X plan for example, so you run different temps for cylinder and UFH. A few factors you need to consider Although UFH can contain lots of water, it is only useful if it's not in lots of zones. The smallest zone is your system capacity, not the sum of all loops. Ideally run weather compensation with all loops open all the time. What is your min and max heating requirement in kW compared to min output of the boiler in kW? How much insulation under the screed, 25mm or 300mm or somewhere in between? All cylinders loose heat, the bigger the difference between internal cylinder temp and the surrounding air the higher the heat loss. Getting the correct sized boiler no buffer required. Get A rated cylinders with 3m2 coil, add more insulation if in an unheated space. Or find room in the house.

It's amazing the difference in outside temperature, between south and north of the UK. But we'll done you on the saving. I really need to get some monitoring done on our house, that could be my new year resolution.

Think it must be opposite up here, the rare occasions it's above 10oC up here

I looked at this when I did and automatic to manual conversation and needed a new Speedo. Think the way it works is, if you install a brand new or used Speedo, you can reset the odo to current milage, but only if you are increasing the mileage not reducing it. So if car has 50k on it and you replace speedo and the replacement Speedo read 100k, your stuck with a reading of 100k. You cannot go backward, with any Speedo, current or any replacement.

Every time the wife sees a house even close the border, she remarks how daft it is to buy a site to small and cram it full, with a house just too big for the site. I must admit I do agree. Think I would look at a narrower, but deeper house or taller. Make it look like you have built in a spacious plot. Give it kerb appeal, for selling later.

Without 120 to 150mm (or more if you can) of PIR under the floor, the heat loss could be pretty large. The boards are 18mm, pipes they are using 12mm, so 6mm of insulation.

If your floor U value is 0.15 or better UFH is an option, otherwise your downwards heat losses are such that the running cost could be huge. Then radiators is the best solution. Also radiators are better for on off heating, ufh really needs long run times to be viable.

Also note what @Seren161 say about timings. We were similar also, but house had no water, heating, kitchen bathrooms etc. So was not habitable. We managed to finish it within the year so started paying full tax at end of year 1. You should only be due the extra tax from June 22. So 6 month worth. I Would 'move in' so to speak, either, you wife or kids, so as not to pay the surcharge.

I have an Atag, super quite, especially when doing central heating. I think Viesmann boilers lets you you do two zones at different temps with different compensation curves as well a different temp for the cylinder. I think the way to have a fall back is to have tcvs on the rads, but set them a couple of degrees over your normal room temp. Then balance the system to get the room temps correct. Worst case, you stop weather comp, set up as normal and away you go. An X plan still gives you the ability to run the cylinder at a different or the same temp as CH.