JohnMo

Just to be pedantic - normally water, depending on vessel material and end user this water is treated to remove certain minerals etc. Large vessels are infrequently tested with air/nitrogen, because the stored energy within a compressed gas. Went to a heat exchanger manufacture once and the heat exchanger (printed circuit heat exchanger) was for a gas service and the company would only perform air tests. The test were completed ex WW2 bunker with 2m thick wall in case of mechanical failure. You had to witness the test via a camera in another building. The walls had big chunks out of then were a heat exchanger had failed in the past.

What are you trying to find out? Our last house was subject to building control inspection, internal doors had round knobs, no comment from them. This time we have lever handles, not expecting any comment on them either. If there is no defined regulation, you just fill your boots and do what suits the application.

Boiler runs on weather compensation, so can deliver anything from 25 to 35 degrees. Boiler just monitors the return temp and gives more heat to system as required. Buffer is just more system capacity, plumbed as a 2 port buffer, with an oversize tee at the buffer ports to act as a hydraulic separator. Buffer sits at about the same temp as the heating flow temp, hotter at the top than the bottom.

If you have room for a buffer and allow it to float on boiler output temp (no thermostat), min modulation isn't the end of the world. Currently with a min modulation of 6.7kW at 30 degree, against an under 3kW demand, my efficiency gas into boiler to heat at UFH manifold is around 110%. So go with the boiler you are comfortable with and is at the right price and can run X plan or priority hot water and a different CH flow temp.

Sorry a bit of a rant, not directed at anyone. You have a designed system, but not everyone does, you need the whole system to be designed correctly to work well. People are stuffing there houses with trvs, thermostats and zoning everything, thinking it's a magic bullet, while also having an oversized gas boiler - I have also been in the same position. Plumbers like to S and Y plans, but it's crap for boiler efficiency. We learn from it, other don't, I now know on a day to day basis exactly what the boiler is doing and how efficiently, went out if my way to install an energy meter at the UFH manifold. Lots don't read the gas meter from one season to the next. Funny thing in most cases when running multiple zones without an alternative flow path the boiler cannot cope and gas consumption goes up. Most boilers don't modulate as much as yours either, very few houses have a LLH, or buffer, most used to use an always open radiator in the hall, but people put Trvs there as well. Modulation, mine at 30 deg flow temps is about 6:1, many are much worse, I needed a buffer, now I can happily supply 0.5kWh average to the UFH when the weather is about 10-12 degs and the boiler efficiency stays high.

Things you need to do or be aware of from what I have seen and read in various manufacturers manuals The minimum open volume of water in the "always open" part of system has to exceed the heat pump manufacturers minimum volume requirements. For example Grant state 30L. So preferably one zone? Noticed in the video reference he installed a buffer as a volumiser. Flow rate through the system has to meet or exceed manufacturer min flow rate and not exceed any defined max flow rate. You may need an alternative to a mixer valve to ensure any supply flow temperature exertion doesn't expose the floor to excessive temperature, such as going from DHW cylinder heating to UFH heating duty. Short periods may be ok depending floor makeup etc. I do notice with my mixer the flow temp from the boiler is always a few degrees hotter than the manifold, due mixing. So this would affect CoP.

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