JohnMo

Do you have an electric backup heater? If you do I would be switching of the control of it in the controller.

Running cost of electric UFH will be pretty much 4x as much as the A2A. Do some work on the A2A replace if needed. All the hard work had been done it's all ducted etc. 3. Storage heater, you would normally have a storage heater in bedrooms?

House is as you describe about 3kW heat loss at -9. But we also have a garden room attached to the heating system with fan coil. We now run WC mode on an ASHP. I am flowing to the fan coil at the same temperature as UFH as it works pretty well. I have the circulation pump on 24/7 and the fan in the fan coil at min speed all the time also. The house floor is basically used as a buffer for the heat pump. Fan coil gets a flow temp of between 22 and 24 most the time and when the heat pump runs up to about 30. A lot on here haven't bothered with radiators in upstairs bedrooms. But I would treat the gas boiler the same as the a heat pump. As in - Design the radiators for low flow temp same as the floor. Treat as one big single circuit and run weather compensation. The bigger the system volume, the longer the run times. Then you need no fancy controls, no mixers run the whole lot from the boiler pump. Do a system boiler not a heat only boiler, then with a decent boiler you will get a modulating circulation pump, ideally a 4 pipe one or one with external diverter on PDHW, so the boiler runs two flow temperatures. Do not do S or Y plan. Run away from an installer that suggests it. Cycling and short cycling are different, a short cycle will use plenty of energy and little heat to the house, normally in the range of a couple of minutes or less. A cycle is the just the boiler doing capacity control, you have a run time generally a good 10 mins or more. Run time defined by system water capacity and min modulation kW. I would look at Atag boilers also. Out the box WC enabled, even come with the sensor. 3 port diverter valve ready. Just need a temp sensor for the cylinder and a single thermostat timer (ideally from Atag) They work differently from most other boilers, as they slowly ramp up to temp, and you can define the rate of rise in degs per minute. You can get full flow temp instantly if you want. And while your at it, do a heat pump cylinder, 3m² coil, so two options keep flow temp down for full condensation the whole heat period or super quick reheat times.

Prior to changing to heat pump, I would run the boiler and batch charge the floor instead of weather comp. So basically used a 0.1 hysterisis thermostat, set flow temp to 35, and let the boiler run, until the thermostat hit hit 20.6 (set to 20.5) boiler would shut off, would get about 0.5 Deg overshoot and house would settle to 21. From 9am set the thermostat to 20 until midnight then set to 20.5 to 9am. Boiler generally restarted at midnight, run for as long as need to get house back to 20.5. Generally 1 or 2 starts per day. This method definitely dropped gas usage quite a bit.

True

Way better quality, nice and thick compared to paper thin.

The things I find interesting The floor consists of UFH pipes in 56T of concrete. So a lot of stuff to heat up. Looking at this in a bit more detail Last time the heat pump ran it stopped at 0630. Sun came out at 1300. Flow and return temperature was slowly falling from the heat pump stopping (circulation pump stays on), and flow temp started to rise at 1400. The flow and return temperature started to rise 1 hour after the sun came out, all window blinds were closed as room temperature started to rise.

Fully inclusive billing amount including electricity standing charge and any Vat applicable.

I have a log of the temperature in the hall. Which is behind the rooms that get solar gain. Our lounge got to 24 peak, currently at 21.2 (5pm), dip in temperature is when I opened the door to outside (OAT peaked at 13 degs) and coincides with the hottest temp in lounge.

Just been looking at ASHP monitor system, it shows the flow and return temperature among other things. Sun has been out since lunch time. You can see the floor absorbing house heat. For context the UFH pipes are at the bottom of 100mm of concrete, the main rooms to get solar gain are covered in glued down oak floor or carpet. The ASHP is in full WC mode with no mixers etc and circulation pump runs 24/7. Rise in temp is 0.5 degs on flow and return (green/red line) over 2 hrs.

If you want a grant, otherwise buy a 4kW Panasonic - job done. Airtight done after second fix is complete.

I used this on my shed, not the best stuff. Have a look at proctor roof shield Yes, I just stapled No need to tape with decent membrane. Copper nail on top, if proper slates, if tiles batons are needed.

No - why not ask him?

But as he says, until air losses are tested MCS will only use spreadsheets values equal to a very leaky house. Needs his air test certificate in hand first.

Just recalculated it 14p per kWh, based cost paid to Octopus and total house electricity energy used from all sources. Just calculating based on the imported energy alone and total cost is 19.8p. The above includes my gas standing charge. Without gas standing charge It's 13p and 18.3p No smart meter, so E7 or standard tariff are available to me - don't get paid for export. Basing payback on a standard tariff of 25p and total house usage and what I would actually have pay, if no battery or solar, we are saving around £1200 per year. Total cost spent on PV and battery is pretty close to £10k, so close to 12 years payback, based on an awful PV production year due to rain most days.

Your 5% vat comes with a bunch of conditions, so check on HMRC website, some of the vat rules depend on if you intend to live in it etc. I may be wrong but worth 30 mins reading on HMRC website.

Well done, where there's a will....

I would be careful with the VAT implications to make sure you can claim it all back. Was there a good reason to do limited company and mandatory annual returns, accountant ect? And higher company borrowing interest rates?

Sorry where do you get that idea. You can live with and make an oversized heat pump work, but the ideal is a correctly sized one. Its very close to reality on our house and our summer house. Good to hear.

Just think your making a job very complex, just follow the manufacturer instructions. The supplement info for the outside sensor attached also. The simple wiring on the second section. With that I will get my coat. WB1B Compact Outdoor Sensor Instructions.pdf

I installed one, for the same reason. We use occasionally, have a mountain of wood to burn anyway. But house is on 24/7 WC, maybe may get loaded when we start to go sub zero.

Yes I realise your drawing is for the whole wiring centre, so is the Viessmann one, letter G representing the wiring centre, it has all the central heating system control, hot water control and interface with the boiler. Your S plan just says boiler stop start, nothing else. The Viessmann drawing shows a switched live through your room thermostat for switch box L terminal to terminal 1. Your drawing doesn't show any such connections. In fact your room thermostat is really doing anything? Dump the S plan and use the Viessmann drawing. Drive your 2x 2 port valves as suggested above via switch in one 2 port.

Your drawing looks way more complicated than the cdt box drawing

I paid £8k for 13.5kWh (usable) full MCS certified install a year ago and prices have reduced since then.

That's interesting, so slightly more than my simple E7 tariff. If I wasn't paying the standing charge for gas my figure comes down to 15p/kWh. But I assume yours is without battery? If that's the case having a smart meter (ours doesn't work) is a real money saver and would make a battery maths hard to justify.