JohnMo

You really need to keep the pipe runs pretty short or you will not get the hot water to the tap before you want to switch it off. Cold main in valve and tee to downstairs manifold and the to boiler. Hot Do you need the downstairs manifold, your runs would be much more simple from the upstairs manifold and

That isn't exactly true. A 100W/m2 UFH system, will require 100mm centres and a mean flow temp of around 45 (or higher) degrees, irrespective of system you use. If the system is particularly inefficient your mean flow temps will be higher. So the downward heat losses will pretty high, the higher the flow temp and the less well insulated the floor, the higher the downward heat loss will be. The downward heat loss is a product of U value, area and delta T (difference between floor temp and ground temp). In a radiator house, floor temp will be 19 to 20 degrees, ground temp around 6 (unless your floor is ventilated then it could be -2 or less), so the delta T is, let say 14 In a your UFH, system, with a flow temp 45 (mean flow temp) - 6 (ground temp) is 39 delta T . So downward heat loss for the same U value floor is nearly 3x as much. Depending on floor U value a bigger proportion of heat will be travelling downwards instead of upwards. Low energy input homes UFH is good, but still more costly to run than big oversized radiators, but high heating energy use home UFH, can be very costly to run, due the the losses downwards.

Do the maths, 100W X m2 of UFH X hours run X number of days.

All my suppliers of services came from direct recommendation of other people on site or I already had previous experience of them as a company, those companies are the ones I took recommendations from. There was two exceptions two exceptions to that, the company that did the roof structure and our standing seam roof covering. The roof structure company wanted a material deposit, this deposit was to be paid to the company building the roof posi rafters. I insisted the deposit would not be paid until I was copied on all correspondence with the third party company and had seen the PO issued. A final payment had to made for material prior to them starting at site. So agreed that as soon as the lorry was parked by our house I would release the funds. Which I did, they started work the next day. The other company and all other companies were paid for work and materials after the work was completed, or I purchased the materials myself and free issued on a labour only basis. How you mitigate for a company going bankrupt, is difficult. Durisol went that way after our build was completed. But having a more normal build you can at least spread your supplier base so all your eggs aren't in one basket.

If you have MEV, dMEV or MVHR extract in the kitchen then you are already covered. Hob extract isn't required. If you don't have a either of the above, then you will need the extract working.

The other thing "the customer always right". Recently obtaining his cert, maybe not enough confidence to push back. Or was he told to plumb the British way - not the correct as designed way?

I went to a guys house in the states (Ohio), we had been off working for two weeks, his house had not been locked the whole time - it never was. No one ever thought about entering, because they were as likely to be shot than anything else.

I would use 25mm insulation as that gives an airspace, which will increase performance and is more generally per installation instructions.

All those years inventing rockets, all they needed was an UVC. And a badly set immersion and a relief valve that didn't work.

This is done with balancing the water flow through the different areas. Not saying you need to do this, as you are happy with your setup; but for others reading this who maybe aren't sure.

I would be careful using you own name and posting photos of yourself. Public forum you have no idea who is reading and watching. Next you will let it slip you off on holiday and come home to an empty house.

Why not do UFH heating and UFH cooling? No drafts. All done from A2W. Run the cooling at a fixed temp say 18 deg, there should be a decent floor cooling effect, without and condensation issues

WC allows the lowest temp flow at all times. So the amount of condensing within the boiler flue increases. More flue condensing more efficient the boiler runs. Our efficiency went from high 80s% to around 107 to 114% efficiency measure by direct consumption and a heat meter.

I would be tempted to keep it super simple, I started complex, used a tonne of gas, went simple after that. I am now using a single COMPUTHERM Q7RF thermostat, a wired version is also available, 0.1 hysterisis, so it shuts of the heating when you want, starts the heating back up when you need it too. Most thermostats have a hysterisis of 0.5 or worse. You can run really low flow temps, with your floor, a downside is the response is slow, so thermostat hysterisis is super important. Smart phone control is just a gimmick you really don't need, in a well insulated home, in my opinion.

How thick is your screed and how well insulated? Reason I ask as it makes a big difference to how the thermostat operates your heating. UFH is very slow to change temperature by nature. Hysterisis is an important consideration often overlooked, and most if not all so called smart thermostats have a huge hysterisis, which may be ok for radiators but are rubbish with UFH.

Scottish larch, coated with Rye oils ceder oil, way cheaper than osmo, equally as good. Real stone cladding - blue stone.

As @Iceverge says let the house settle, would try it without a buffer for now, has he plumbed to allow your boiler to run weather compensation? if you add a buffer I would install as a two port configuration in the return line coming from the UFH. So in the pipe between the outlet of the UFH going back to the boiler. That would be easiest and most efficient. Would get him to do the pipe insulation properly it's a mess. Every gap is an energy loss. All the changes of angles should be mitred. Assume the photo is in the loft?

No sorry no build thread. Rear of house is done in stone slips. A couple of photos

Thanks for that, good to see. So for a like ACH there is circa 100W difference between MVHR and say a dMEV fan. So take it we have a heating season of around 6 months. .1 x 28 x 6 = 16.8kWh, assuming electric heating x £0.34 (electric price) that £5.70 per year difference. If heating by ASHP, it would be a third of that so £2 or less.

Mine is on a thermal store, not sure that really makes much difference, but our our outlet water goes out via a temperature controlled mixing valve. Safety not sure on that. If I had mine set at 60 for a so called legionnaires cycle, I would hit the low 50s so that's not good for that safety cycle. Poor design - Or is the PV diverter putting out a smaller kW than the design of 3kW, so the water flow around the immersion not per design intention?

And the decking. Frame is doubled up 7x2, other wood 4x2, at 300mm centres with composite decking boards on top. Steps - step made from an off cut of our main gate post, 10" square Scottish larch about 1200mm long, bottom landing area of steps will be a slab of 60mm Scottish larch, not the black mesh in the photo.

Plasterboard taping underway.

I paid £1000 for our gas boiler in a sale, and paid £1300 for the ASHP from eBay, the plumbing is basically the same. Two pipes connected to the heat source, supply split via a 3 way valve diverter, one to cylinder and one to UFH. And a return pipe. Thick slabs are slow to react at low flow temps, our is 100mm, but with 300mm pipe spacing, if you rely on a normal thermostat for each room, your house temps are all over the place. You need a 0.1 deg hysterisis thermostat. We are running just one thermostat, and for the past month or so we're batch charging the floor overnight with weather compensation and using the thermostat to stop the floor heating. Generally the heating cycle was 7 to 9 hours heating on, the rest of the day off, house temp pretty stable.

It could be the thermostats in the heating element, it could be seeing local temperatures at the set point, but the cylinder isn't at that temp. My view it's just a rubbish design that is just copied. No-one ever really looks at the temp, except some on here when they are trying to use excess PV and it doesn't go to plan.

I would look to dump the buffer, but would not install bypass valves, I would ensure a proportion of the rads stay open, so take any trv's off a couple of the bigger rads, so you have good size of system always open to the heat pump, if room get to hot fine tune the lock shield valves to balance. Or better still modify the WC curve downwards, so it reduces overall flow temp. Are you running weather compensation? This would help the overall SCoP, if you are not.