Nickfromwales

Ok, then does the combi not fire DHW to all outlets via the buffer? Eg when any hot water tap is run, the combi diverts to DHW mode?

Too much off the ears.

Ah, so not a Combi boiler, just a combi-nation of components. Gotcha Now I recall your setup, sorry. Been a looooooong day.

I would, but I'm washing my hair....for a few hours. It's on my to-do list though, and I'll not forget!

Exactly what I came up with. You literally JUST beat me to posting that.

You've described @Dave Jones to a tee Which was one of the main reasons why I have mentioned gas tbh. 22.5 kW of microgeneration ruffles the feathers, then add EV charging, and THEN mention a whopper of an ASHP and they may well shit the bed. Prob be a good idea to choose a PV system where you can volunteer to accept zero export. Wipes out toying with Octopus etc though. Cracking idea, and perhaps could be further simplified by just doing that from a huge UVC stored at 40oC?

That will be sized, most probably, to the electrical requirements of the house, with most of the excess feeding DHW or topping up the battery. Can you fit more PV?

If you say @SteamyTea three times, he will appear.

Diminishing hot water? When the combi registers DHW flow the pre-heat circuit shuts down and the volume of heated water starts to diminish rapidly.

Sounds like a huge expenditure on equipment with limited service life. Probably a high-temp split ASHP would be better CoP-wise? How much PV / battery do you have? Or have you not bought and installed anything yet?

The ASHP won't have a CoP of 3 or 4 when driving DHW at 65oc, more like 2 if you're lucky, and that's if it's not winter and the air is freezing / damp and the HP freezes over from charging this HUGE volume of hot water. This needs a serious re-think in honesty! Winter PV will do next to zilch too, unless you're installing north of 12kWp on 3ph. Do you have gas available? I think you'd be much better off with gas for this scenario.

You wouldn't mix them, but it is very dependant on your consumption patterns / peak DHW demand at any one given time. Excess solar from 9kW will not leave much to go into hot water, as I am assuming this is a very big / multiple occupant dwelling (?) to need that much DHW? I'd look at a pair of 400L cylinders, with the second for DHW and the first for DHW pre-heat. Putting pre-heated water into the 400L DHW tank will probably double its useful capacity. Can we have some more information about house size / occupants / number of bathrooms etc?

Do you have a drawing of what you have detailed?

I use Vortex, and bulk buy when stocks are dwindling. I just look for the cheapest online supplier that will delivery FOC at a certain purchase point. https://www.bolts.co.uk/5mm-x-50mm-woodscrew-vortex-pozidrive-countersunk-ybzp-pack-of-200-p-WSPCPVZY05050/?keyword=&matchtype=&device=c&campaign=GS_|_Woodscrews_-_Vortex&gclid=CjwKCAiA3pugBhAwEiwAWFzwdaRPlnMfus-nZpbAc-HwOkn0V6C05tOOHnt8FGZACZNDSlFB3fVl0RoCGOoQAvD_BwE

which brings about the question of The less the need for heating, the higher the likelihood of needing cooling. Have you done a room by room PHPP analysis?

You could use an "in screed" heater wire, if you want utter simplicity. The caveat is that an ASHP could never be retro-fitted, which leaves you completely reliant on some off-peak tariff or other. I am not sure of what heat pads you mean, but you defo do not want to heat the immediate upper surface ( as that will take much longer to heat the entire mass of the slab ).

Yup, on the Brink stuff, but a pretty generic function. You were probably just giddy from the good news 👎

I wouldn't get too upset, as most trades know little or nothing about airtightness, in fairness. To solve this, all you need is a squirt of Illbruck 330 foam and it's job done 10 minute fix.

CT1 is still the bomb, and Sikaflex will be around long after me I expect For a tray on legs, you have to go to town on it. Bonding the legs down is the norm, but I also install a rip of plywood along the X & Y edges which I glue and screw in place. You dry fit the tray and level it, and then draw a line under the tray with a sharpie, and have the plywood ( 18mm ) sitting on the floor and just stopping shy of the line. Set the tray into wet CT1 ( detail as per the other threads ) with a generous amount on the upper edge of the ply, plus on the wall, and also run a bead along the X & Y edges of the tray ( on the rear not top ). Push and wiggle everything into its final place, and job done. The belt and braces approach is to follow the previous recommendations and make a base and lose the legs altogether. Just needs some good woodworking skills to create a space for the trap, support in the right places, and an escape route for the pipe run. Have baby wipes to hand to clean up, and use loads of them to keep the mess at bay.

I have, once or twice

Only that this is exactly what to see / expect The slab is porous, and will suck the diluted primer like Gillian Taylforth, so nothing to worry about there, just keep lathering it on until the floor gets as saturated as you can get it. I always get the SLC down over the floor whilst the diluted primer is still wet ( so not technically cured / left to dry ) which I find leaves the SLC to flow far more readily. Also, if it's a 2-part SLC with the 5L of addmix, I always throw a 1/4 pint of water in to the mix immediately before pouring. And whatever you do, don't run out of SLC 🤣

Get cracking then! 🙄 😁

Glass half full time There are many, many people worse off than you. Struggling a bit to build your own home is par for the course. Just sit back and enjoy the ride, as you can't get off until it's ended. Buy materials now, if you fear they may go up, but then repent at leisure if you find they then came down instead, or something better came out. Timber and inert stuff won't really matter, but if you extend over time then your salary(s) will chip away anyways. You will need an electrical completion certificate, same ventilation and drainage. You'll need a very basic kitchen with an oven and hob ( free-standing crap 2nd hand electric job will suffice ) and one bathroom. That's it really. Heating can be via plug in radiators etc but sense should prevail around what you 'don't do' before occupancy, as moving in when massively incomplete is progress-suicide. It is what it is, so preserve the bathroom(s) and flashy kitchen for later down the line, possibly funded by a remortgage post completion? Concentrate on the fundamentals, and leave cosmetics for now. Function instead of form, and invest wisely in the infrastructure as it will be daft to have to redo anything such as heating or hot water. Run cables for PV, install later etc.

which will have 20% VAT, which you can reclaim.

Your logic is flawed here, IMHO, and gets worse the longer you intend to stay in this property. Lets delete solar PV from this equation for simplicity, as in the winter it will have little to no effect on heating, ( unless it is a considerable array ). Installing wet UFH into a slab you're already having, is a way to introduce ridiculously low heating costs, so in order to "justify" it, just get a calculator out and do the maths. Look at the costs of heating, coarsely, with grid cost 1:1, and then look at doing the same with a HP at 1:3.5 - 1:4. That's a 1/3 of the costs minimum, and the cost ( and inconvenience ) of panel heaters ( which you absolutely will NOT be able to sit anywhere near to ) and the VALUE of how you will live with each choice in your HOME. Then suffer furniture plans being definitive, and that's the end of the choices then, for me, anyways. Then factor in load shifting for an off-peak tariff like E10 etc ( 3x per day ) via the HP ( multiplied by the CoP ) and you should see running costs as low as a few pence p/kWh. Your proposed heating arrangement would soon be up at 50p/kWh eg 10x the cost. Now can you justify it? THEN, factor in slab cooling for the summer which you will get for free as a side-effect ( aka bonus ) of owning an ASHP, plus putting you furniture wherever you want. Also, the heat emitted by UFH in a low-temp slab is a thing of complete and utter beauty. The heat emitted from IR panels is, IMO, "ugly" by comparison. A colleague of mine recently installed the smallest IR panel he could buy, in his small home office, and after suffering skin issues ( he said his eyelids were literally cracking ) he has had to remove it and go back to an oil-filled panel heater. It matters not one tiny bit what you decide to go with, just my 2 cents. FWIW I have been installing space heating into passive houses ( or thereabouts ( or way above also )) for over 8 years now, and I would never ever steer away from wet CH, nope / nil / nada.