sharpener

No panic. You will want to take the shower cold feed from the balanced cold outlet on the unvented cylinder, the basin and WC can be either bal or unbal so usually easier to make them all balanced. Probably there will be a stop cock or lever valves before the UVC, turn them off then open existing hot and cold taps to relieve the pressure, they should quickly give way to a dribble then you have succeeded. If you can open taps on first and ground floors then the 1st floor pipes will drain down into the g/f pipework and comparatively little will come out when you cut into them. Make sure you have correctly identified the rising main going to the UVC though, it will still be under pressure.

Yes, +1. A single drop of 3-in-1 on the thread before you fit/tighten the cap nut means much more of the torque you apply is turned into axial force that in turn compresses the olive. I also find the thinnest of smears of old-fashioned jointing compound on the olive is all that is required for a perfect seal yet easy to dismantle. The rightful place for PTFE is mostly in the tool box, occasionally for male-female threaded joints.

Marginal cost of a bigger boiler is small. Often dictated (or so ppl thought) by HW requirement. Neither true for HPs. Well Michael Podesta's method of dividing annual gas consumption in kWh by 2900 couldn't be very much simpler. Heat Geek cheat sheet method of estimating from sq m and type of building construction is a good way of sanity checking. Problem with retrofit is determining what the actual construction details are e.g. how much insulation is under the slab, and actual air changes/hour. Test methods exist but cost £many 100s, and some can't be done at some times of year so ppl aren't in the habit of using them.

For those who don't like the idea of a plastic bodied pump this is the best value bronze one I have found. Can also be turned down to much lower power consumption than the Wilo, see the graphs in the link.

Not really. It will have a filter screen in it which needs to be looked at occasionally but mine gets very little debris so once a year is enough. You need a balanced cold feed to all things like shower mixers. It is useful to have mains pressure at the kitchen sink and any outside taps so in practice it may be sufficient to pipe it to the upper floors. Unlike bath/basin fittings kitchen mixers do not actually mix within the tap body (Water Regs) so this is not a problem.

I think it became clear from that thread that ppl on here are much more clued up about the benefits of PEX pipework than the average plumber. Good luck with your project!

There's a lot of relevant discussion on this thread.

I guess marking the pipe with the intended depth works just as well as it does for Yorkshire and compression fittings. But ugly in comparison. Have only used once but the Sprint looks almost as neat as Yorkshire. From choice would always use Polypipe or compression if I knew I would need to take it apart. Unlike some others the grab ring in the Polypipe fittings is beyond the O-ring so the pipe is not scratched where it seals.

What do you think of Tectite Sprint vs press fit? I know the latter are very popular now for professionals, but for DIY the tools are prohibitively expensive. And for a small job Tectite are very convenient.

Well he may not like it but if he had the spec from an M and E consultant to quote against then no question that is what he should be fitting. OTOH I sense this may not go well.

Doesn't have to be like this, works OK with conventional tree/branch config also. But it sounds like yr plumber is new to plastic, mine treated it like copper and used pressfit elbows everywhere rather than using bend formers, must have cost them (?me) a fortune in extra fittings. Yes where they are on show I have used copper drops for perfect straightness and fewer clips, but plastic everywhere else under floor and in garage. Personally I don't like JG Speedfit, my rainwater system had a lot of them in it, early ones were not v secure unless pulled hard tight, now they have locking clips I think. Polypipe fittings much better, I thought Screwfix no longer stocked them but I see they are back again although much more expensive. Haven't used Hep2O but they do look neat and less agricultural.

Ideally run a 10mm pilot drill through from the outside, then finish from both ends with the 22mm, avoids bursting the corners off the bricks and so causes less damage on the inside.

In a word yes to all you propose. I used what appears to be an identical fitting from Screwfix, works fine. To avoid cracking the bricks I put the hole through a T-joint in the mortar and got 3 good fixings in the 3 (almost undamaged) bricks. Most worrying step was cutting to length and fitting the elbow on the inside, bc to get the pipe to run close to the wall I used a Tectite fitting partly buried in the plaster and they are not re-usable. I see no point in insulation through the brickwork, will serve little purpose, in coldest weather you will have it drained down anyway.

Thanks, convincing and well presented. V interesting that the USA is in more or less in the same (poor) position as the UK even though their existing technology is quite different. I am supposing this is a warm/cold air ducted system as there is no mention of emitter type, condensing operation or WC. With a hydronic system measuring the "call for heat time" would be an over-estimate bc call for heat does not equate to firing, a boiler would shut off on its own thermostat and cycle/modulate to keep its setpoint. However measuring gas consumption as per Michael Podesta's method equally valid. -24C OAT! We hardly know we are born in the Gulf-Stream-washed UK do we? My design temp is -0.2, admittedly that uses stats for Plymouth. Have seen - 4.9C one single day in the last ten years. Plenty of secondary heat sources, although not permitted in MCS calcs. Tools called "measuring tapes"!!! Wonderful how they still intermix metric and imperial units, 2 tons HP equals 7kW, who knew?

Yes. Where and what type is your existing inverter? If in the shed and it is connected via AC cable to the house there is no particular problem. Even if there are other loads in the shed, a CT in the house will measure the net inflow. The GivEnergy Gateway is a quite flexilble solution for connecting it all up though not the cheapest. Alternatively you could lay DC cables back to the house and connect them to a hybrid inverter in the house. This forum also has a lot of good stuff on it and some members have very large and very complicated systems.

This.

Many HPs have a noise reduction mode which produces less output in a slightly more controllable way. Or buy the dhw tank you will eventually need (with a big coil to suit the HP). Pipe it up temporarily as a buffer/thermal store and draw the dhw off through the coil while you are living in the office/store.

https://www.screwfix.com/p/flomasta-compression-adapting-female-coupler-28mm-x-1-/96133

Sounds fairly suitable, see the Q&A here, they recommend some re-inforcement for >25mm dia and the joint has to be dry first and then left for 1 - 2 hrs. However this will/is intended to form a seal on the threads. Personally I would want to understand how the existing seal is supposed to work, probably axial compression of the washer, and then improve it. Check there is no damage/distortion to the mating faces or a tiny sprue left from the moulding process. Often the washers are too thin/too hard, a circle cut from an old inner tube might be better and less likely to get pushed out of place. Or apply a thick bead of silicone sealant inside the cap, screw on lightly and then tighten 2 hrs later once it has set.

So you will get better efficiency out of your existing setup if you heat the DHW at times you do not need the heating on e.g. the small hours. The diagram you drew does not show pumps on the DHW or rad circuits. The are probably not necessary anyway, and almost certainly not with a heat pump. Your setup is otherwise similar to standard HP schematics and therefore conversion to a HP should be quite simple, assuming the pipework will support the much higher flow rates (HP will have only 5C delta T so require 5x the flow to transfer the same amount of heat). I have a similar basic setup on a 30kW oil boiler which I am planning to replace with a 12kW Vaillant Arotherm Plus but your heat losses are too big for that. Avoid hydraulic separation if you can (and especially CCTs), probably not required in any form and a cause of inefficiency for fundamental thermodynamic reasons. Existing mixing valve on UFH circuit is all you need to cope with the different flow temp requirements.

A full 200l tank of water takes about 9 kWh. For 9 people you should allow 9 x 45l so at least twice that. With a 12kW HP it would spend 1 1/2 hours in 24 heating the water which is a big dent in the heat avail for space heating. Gonna take a v long time.

Did that include any allowance for heating the DHW? It can have a material effect on the sizing depending on # of occupants and usage pattern. Also an MCS installer may insist on changing the tank, what have you currently got and importantly what is the coil surface area?

Lots of ways to do this. If the pipe runs are suitable a two port valve is simplest, could power from a Shelley or similar wireless gadget to save a long/difficult wiring run. Set up as a separate Circuit on the Vaillant controls, can then have its own time/temp schedule. Or wireless zone valves or TRVs on the rads, Tado are probably better than my Honeywells (could hardly be much worse!).

I have used DIY tests from Simplex Health, they despatch promptly and there is a wide range available which are relatively easy to use (helps if you have done some wet chemistry). The lead test is very sensitive. Have also used an independent consultant but he sent the tests off to somewhere else and didn't really give me the advice I was looking for (low pH in my rainwater system). If you have hard water I would not worry but as you are in Scotland you might have a problem, OTOH if so they probably treat it with polyphosphate - which is what causes the scum on your tea if you suffer from that(!).

You don't say what emitters you have got on your wood-fired boiler system which would be useful info. My initial thought is not to try and size an HP for the full duty for the reasons you state. As @JamesPa says, if Floor 3 is indeed above Floor 2 you may find depending on the construction of the floor that is is heated from below anyway. Maybe plan to heat the core from the HP and in extreme low OAT either run the fireplace, or if necessary add an A2A HP for Floor 3 later. The problem may be in convincing an MCS installer to size it like that, bc to get the BUS grant it must be designed to heat the whole house from the HP and installed by an MCS installer. I eventually got mine to adjust their assumptions a bit, their initial quote for my 200 sq m barn conversion was for a Stiebel Eltron 15kW unit. Here is some data for the Vaillant Arotherm Plus 12kW which is what I am now planning to fit. Water temp 40 - 45C. Other tables available here. You will see the modulation ratio varies with air temp from 25 to 50%, that is pretty typical. Mitsubishi publish similar tables, but they are hard to find for low end products. Avoid Samsung, they quote a wide turn-down ratio but use hot gas bypass to achieve it which wrecks the efficiency. The Vaillant spec is quite generous and it actually puts out 12.5 kW at your -7C. As you can see from the table below it will even do 14.7kW at OAT = -2 if your emitters are sized for W = 30 - 35C. There is also a 10kW version of this HP but it is the same mechanically with the output restricted by limiting the compressor speed to 85 rps so not much cheaper and the ratio is worse.