Nickfromwales

A pic or two of the roof would help with that. An aluminium frame would distribute the negligible weight so all problems that can. be solved. The fall-back solution is the Heatstore combi. Instant, constant high-flow DHW. Not a compromise imo either.

What about achieving grid-tie with that arrangement J?

Size vs expected demand basically. The heat transfer rate of the boiler > coil > UVC wouldn't match the rate at which you could consume it at peak times of DHW demand. Something folk seem to forget / not mention much here is that a correctly sized TS and a chunk of a gas boiler will give you nearly constant DHW...eg bath, after bath, after bath or two - three ADEQUATE showers simultaneously with ease. Basically you look at the TS as a big, wet, high-flow combi boiler. As heat is consumed from a TS its replenished by the boiler. The size of the TS and its target store temperature dictate how long it'll provide 'continuous' DHW for, so are factors applied to each enquiry, as no two are ever exactly the same. A TS is a one tank solution for your requirements here, so capital cost is lower, functionality and simplicity is maximised and loss of valuable space is reduced by not having two cylinders to install. Sorry, my fault for the lack of clarity When I refer to cylinders then for ufh its just a buffer you need. I only refer to a TS when its providing both heating and DHW as otherwise it would just be a 'dumb' buffer. In this instance the TS would be providing space heating ( buffering of ) and DHW via an instantaneous DHW coil inside it. Therefore id size it to match the intended UVC size plus the assumed buffer that would have been required and go for one, prob 500l TS. A few will gasp at the thought of a 500l TS, ( roughly 1800mm H x 660mm Dia ) but going bigger will mean you dont have to keep it at the very high temps it would need to be kept at if it was smaller. Therefore the standing losses would be lower, and the latent heat issues would be reduced. That 500 would be if there was PV. 250-300 without. The next bomb-drop would be just fit a chunky buffer for UFH buffering, and maybe fit a coil in it for DHW pre-heat, and simply fit a Valiant 938 heatstore combi. If theres no PV id go for that in a heartbeat. You'd only be storing water at around 40oC then so very little latent heat loss then too. And another bomb...... DHW flow rates are all dictated by the incoming cold mains performance, so pointless planning a solution for 20+ litres per minute outgoing if you've only got 12 or 14 litres per minute coming in. @divorcingjack, do you know what your static cold mains pressure, and l/p/min flow rate are? Pretty critical base criteria for anyone to suggest a solution. Gas + UFH is the ball-ache here imo, so its making the best of what you've got.

"During the war, Rodney" @JSHarris Would a flat roof not have a reasonable yield as its facing the sky at the end of the day. Partial shading of differing areas of the roof, and panels with micro-inverters would still see a return from the incidental / indirect sunshine as well as the limited direct imo. DIY job with loads of it and consume what you generate?

Intersting, but that would clearly just leave the OP short, or out of DHW..... plus as per my last, you do NOT want the boiler modulating all winter to follow the ufh demand as you'll be way out of condensing range. You need to do the maths. Guessing isn't as good as finding out it IS worth doing. Remember you said this is a life property so thats hopefully a long time and a lot of grid gas and electricity to buy, possibly into retirement. Could you not just ring the planners and ask them outright?

Have you done a survey / estimate on the potential yield anyway? If its a flat roof and you smother it, plus use micro inverters, you'll get some yield surely ? Someone posted an online doo-dah to work this out....anyone?

This is where i cause murders, because I would put a much bigger boiler in, a 300L TS and do away with the buffer tank. Your enemies here are your expected DHW needs, eg it'll likely be all in the morning, a bit thorough the day, and another load in the evenings. If theres 4 of you then I would suggest the bathing may well be back-to-back and even simultaneously at the peak Having no PV in a "for life" property seems a bit counter productive to me, have you had that as a planning condition or just discounted it because of the cost ? Sunshine will remain free, gas will rise continuously. Id seriously rethink that approach as a zero-renewable solution isn't ideal imo. You dont want the boiler to modulate down as far as the ufh would need as you'd then be outside of the condensing range and your efficiencies would plummet. The TS would be set to sit at around 65-70oC, return set to sit around 50-55oC and thats achieved by pulsing heat in in chunks rather than trickle charing as its consumed.

Now theres a reason to go to McD's instead. Yuck.

IIRC, thats @Barney12's new outlet to pay for his build

My kids used to say, "Daddy, isn't it true that its only the really old animals that are about to die that we eat?" and I'd reply "Yes, of course"... There id say "You enjoying your lamb dinner?" and 4 smiling faces would spin around and say..."More please! And dont forget the mint sauce"

Still scratching out a list as all the various bits of info starts to settle. Have to keep re-reading this to make sure we dont overlook anything. Coffee No.2 is helping. I beg to differ. At least they only slice up the chickens before serving, but McD's seem to go through a de-nutrification process where anything of any nutritional value is sucked out. I leave McD's hungrier than when I go in. Give me the chicken any day of the week.

Dont you mean a McKFC ?

The voddy will take the edge off both. ?

We better shut this forum down asap then Just like the haggis.

Ill bring some pot noodles

Some interweb stuff : • Glycol Propylene glycol is non-toxic anti- freeze. Brands designated for solar have re-soluble inhibitors. The inhibitors prevent the glycol from becoming too acidic for the pipe. The glycol should be rated for at least 325 degrees. It will keep its' integrity for 5 years under normal conditions and less per occurrence of overheating conditions. When glycol degrades it becomes acidic enough to eat through copper especially where there is extra friction in the pipe such as at elbows. It also loses its freeze protection gradually, as the inherent chemical compounds eventually separate. And for @JSHarris this wee gem... Thermal mass Excess heat produced during summer can be stored in sand, earth, salt or water for use during winter.

Might be best to stay sober.......for the first hour anyway.

Im on the research, so will update again shortly as im due to do @AndyT's head in again on Monday with my 3rd round of "and what if I do it this way?" questionnaires.

I think it'll be fixed before that !!

I draw the line on having to have to catch it then eat it. In Scotland there must be a McDonalds ?

I could slum it I suppose. Do they have bacon where you live ?

I think if there were any ZV's we'd have seen them by now tbh.

Out of the mouths of babes..... Half chocolate coated malted milks, obviously.

@Onoff Just being mindful that this circuit is feeding 22mm flow and return through the house going to 4 x UFH manifolds.

Yup. leave that deal with the c-curve of the pump rather than the not great relays on the HM PCB's. Cheaper and easier to replace the ZV head too.