JohnMo

That really should read Uw not UG. 0.6 Ug, in a poor frame could be 2.0 Uw in a very poor frame.

Yep rockwool type material - not PIR, otherwise you will hear every noise from above. Plus as said noise is covered in building regs.

Worth a read, started as mlcp https://forum.buildhub.org.uk/topic/18834-unvented-cylinder-installation-spot-the-problem/

I have two MVHR units, one with the inlet/outlet facing the prevailing wind the other not. Both use a combined inlet outlet unit. We are also on a hill so get some big wind. Never noticed an issue

Obvious question is why would you even want noisy on demand extract, when you can have silent dMEV. Greenwood Airvac CV2GIP can be had for £40 to 60 from eBay. Bathrooms and utility only need them as long as you have an extract cooker hood. Need to ensure you have circa 8 to 10mm undercut on the doors, but that should be there anyway, other wise your on demand extract is rubbish. But must say world is going mad, when someone wants to make there house leak more.

A buffer and LLH can be the same thing depending on how they are plumbed. A LLH provides hydraulic separation between the heat source and the heating system. It needs to sized and the pump rates either side also need to sized correctly, otherwise huge efficiency hits are seen. You also have a secondary pump in the system, which runs when ever the heating is on. The solution I provided, does not need the secondary pump.

Good old Ebay purchase. Mine is a 6kW Maxa heat pump. Like @prodave says super easy to install two pipes, one to a 3 way diverter valve the other is the returns to ASHP. Height of winter no they will not achieve 400%, but overall they can and do. The advertised SCoP for my heat pump at 35 deg flow temp is 4.26. However CoP at 2 deg and 30 flow temp is 4.26. While at 7 deg a flow temp of around 26 will give a CoP of nearly 6. Add into the mix solar PV and that is offsetting running costs throughout summer and some summer months. I know solar thermal will make your DHW, but PV is making my hot water and providing cooling and offsetting my daily running costs for electric. In fact since the ASHP install, my electric bills during the summer are unchanged from last year (no ASHP last year - installed May 23). This year I am also running cooling (through UFH pipes) via the heat pump most sunny days for 6 to 8 hours, the equivalent of CoP for cooling, is around 6 while cooling, but PV is supplying the electric, so zero running cost. My immersion has taken my cylinder up to 80 the last couple of days, via the PV diverter, heat pump hasn't done any DHW heating. Even if you store water at 46 degs, they only recommend you heat to 60 weekly, this can easily be done by immersion, but its questionable if you really need to in the UK, unless you have immune system issues.

Not the best frame for getting close to corners

Those fittings are used for string. All you need 2 x 2 pin picture hooks and the string. B&Q or your local picture framer sell both.

Screwfix do a decent Harris kit. Rollers, frames and an extension etc. You will a decent sized roller bucket and brushes also.

Something like Hep2O and copper where required. If DIY use Tectite push fit for the copper and Hep2O push fit, within Hep2O and interface between the two materials.

2 off double pin picture hangers, if has string hanger at the back. If it's really heavy it will have hanging plates on it, then Rawlplug and screw.

Basically what's under the insulation is the ground at approx 6 deg or if block and beam outside air temp. The room above the ufh will be circa 20 deg. At the same time the UFH pipes will be circa 30 to 35 degs. Heat tries to move from hottest to coldest, so temperature flow is always trying to move towards the ground, reluctantly moving upwards. The more insulation you have the lower the flow temp you need. The lower the downward heat loss, which can be big with UFH compared to radiators. 150mm compared to 200mm is circa 50% additional downwards heat loss. The run off time to get hot water could be long. I am using 16mm and that wait can be long enough. My floor build is 150mm reinforced concrete, 200mm insulation, 100mm fibre reinforced concrete. I ran my pipes in flex conduit tied to rebar and cast in place. You need to run conduit so in theory they are removable. I took my DHW pipes up and ran above ceiling level

I paid £1300 delivered for the ASHP. 200% efficiency in a new build is rubbish, should be circa 400%, flow temps should be never exceed 35 deg (at -9) except when making hot water ASHP maintenance, give it clean, get rid of the leaves and debris, clean the filter the in the water lines. Done In a well insulated house loop centres make little or no difference to flow temps required - maybe 1 to 2 degrees. I am running 300mm centres, only require 35 degrees at -9 to keep house warm. All fully calculated in LoopCad. Oil boiler, thermal store, gives a long burn, no buffer needed, less messing about getting jetting right r making sure the sizing is exact, can just run flat out if you want.

Basically if you hook it up as per Kensa, only excess flow goes through the buffer. So when CH is on, the flow will more or less sail straight past the buffer, but will still heat the volume of water. When you only have UFH heating on, quite a lot of the flow will go through the buffer, but that is why its there. 20 to 25L should be an OK size as a minimum. The bigger the buffer the longer the run time of the boiler, the more efficency gained.

I made my own buried pipes after seeing the thermal rubbish on offer for stupid money. 28mm Hep2O pipe, 25mm thick black foam insulation, aluminium taped, inserted in 110mm flexible pipe. Sealed at found level with stainless steel mesh and spray foam.

Can you upgrade to 200mm insulation? Put cold water pipes below all insulation, pipes need to in conduit. Run pipes from a cold water manifold. 200m2 why would you need 3 manifolds. One should be fine, doesn't really matter the layout. Add electric towel rads to the design also. Why oil on a new build, I did gas and now have ASHP, it comes with the benefit of cooling also. Oil isn't the smart way to go, your heat loads are such that you will struggle to control the boiler without going thermal store. Ashp, operate as a single zone, no buffer, UVC and 3 way valve, job done.

Could you go through the garage? Makes insulation of pipes easy. Underground is doable but would steer away from that if possible.

I have some glazed doors in krypton double glazed the whole door U value (Uw) is 1.0.

Think the main issue is even the good steel frames they are pretty rubbish thermally. You need to get the Uw figures. Passivhaus windows are going to be around 0.6 for the whole window, I looked at steel framed triple glazed and was circa 1.2 to 1.8 if memory is correct.

Here is a link to kensa heat pump talking about buffers, have a read. Don't worry it's talking ground source heat pumps, it's also relevant here. If you install per the guidance on the web paged link below, it will act as a min flow device and volumiser, which is what you need. (Ignore my previous advice of installing in the return line only as it does get you away from the min flow required. You should aim to install between 15 and 25L sized buffer/volumiser. https://www.kensaheatpumps.com/installer/buff-up-your-knowledge-of-buffer-tanks/ Something like this could be ideal (below), tee from flow from boiler, into top connection, and a tee from return in the bottom connection.

Switch on heat pump, look at the flow meters on each loop - are you getting the expected flow rates. If yes they are ok, if not, they are not suitable.

I booked an appointment last week, they come on 26th September to install, so just under 4 weeks.

Aren't the error messages a thing that occured several years ago and are now fixed? Needless info in the first post? The point of the post is when only UFH is engaged the boiler only runs for a minute then switches off - repeat, when he engaged the radiator also the problem goes away. Two UFH loops alone (possibly 4 to 5 l/min) will not keep a boiler happy, hence the short cycling. My boiler was looking for around 18l/min. To support a boiler that can turn down to say 6 kW you need around 50L of water (the posters boiler looks to have a min out put of around 7kW), those two loops will be around 25L. So you have a low flow rate, would suspect the water is just short circuiting via min flow valve and no water volume.

Leave that in place, let your wife twiddle to heart's content, just don't connect to the heating system.