Nickfromwales

Only real negative is the extra heat loss from having this open to atmosphere. @JSHarris' blog highlights this in detail.

Telford vs Newark eh? There's only one way to settle this............

Just to get a more uniform delivery from the heaters. Two in parallel would require the pipework to each heater to be near identical to guarantee even flow through both heaters, just my OCD from that point probably. More on point though, with the series arrangement the secondary heater can then also be set to a much lower temp to 'kick out' when the system is up nearer to operating temp = or < the 3kw of one heater. Should add longevity to the system as the secondary heater should spend a lot of its time off as it'll only really be needed for starting the system from cold / adverse conditions. IMO it's better to have one running near constant than two switching in and out like yo-yo's.

Any cylinder holding stored, heated water that is sealed and pressurised, needs G3. A combination aka open pipe TS does not. Im a Telford man, and I prefer the fact that they make theirs out of all stainless steel. As far as bespoke goes, Telford manufacture to each order using their basic dumb cylinders as the base for each order. The cylinders are off the shelf but you can specify where the tappings go, within practicable reason, at no extra cost. Turnaround time is still less than a week from placing the order iirc. I see zero benefit from the tank in tank ( TIT for short ? ) option, with its reduced capacity for the same size cylinder. Id only go for the two tank UVC + buffer option if there was an ashp involved. With a 37kw oil boiler I'd be really worried about such a small second vessel as the oil boiler performs best when allowed to do a long burn at full wallop, rather than cycling in short bursts, and would reheat a 100L buffer very quickly indeed. I'd go for a single cylinder stat to stretch out the hysteresis of the on / off cycle to further promote this.

Ok, another option for you. The vailant gas valves will switch to LPG in the time it's taken to write this. It's just a screw adjuster on the side of the gas valve, and the circa £7-8 for the 'LPG conversion kit' just buys you a yellow sticker saying "Converted to LPG" !!!! If your gas meter is going outside then just hook up a 47kg bottle/s, connect it accordingly to the 22/28mm gas feed to the house, and run the 638 on LPG for the meantime ? Oh, and tell your plumber the Willis heater will do the job for space heating, as long as your reasonably insulated and have windows etc, it'll just take a full day to get up to temp. If it's struggling do as I say above and fit two. Edited to add : check with LPG gas regs, iirc you may need an internal emergency gas shut off valve ( EGC ) and an internal test nipple. Your plumber will know this if he's LPG qualified.

@Crofter is doing just that in his modest holiday rental . Just size the cylinder bigger for a bigger let ? If in any doubt, just fit 2 Willis heaters in series, not parallel, and then you've got 6kw. . Cheap as chips and you'll sell them on when your done.

3kw Willis heater ? 5 minute retro fit into your intended system and near zero doing / undoing and no pointless boiler installing. .

Fibaro

Size the TS as small as you can, as a suitable gas boiler can easily match your max demand eg space heating at nominal draw plus DHW being run simultaneously at typical max flow. The only reason to oversize it would be to dump excess pv into it, so best to commit to pv so you can design now accordingly. The last 500ltr TS i fitted was in a 4 bathroom house and I complimented that with a Vaillant 637 ( 37kw ) system boiler. Even though it will very rarely see full demand it is capable of regularly delivering as little as 9kw whilst fully modulating, however you need to avoid full modulation to get the operating / return temp into the realms of the optimum for condensing to occur. By using a TS you can set the boiler to come on at the premium flow vs return temp to maximise efficiency. That basically means the boiler pulses heat into the TS, controlled by the cylinder thermostat, rather than 'trickle' heating linear to the current demand. That said I'd say you can get away with a 300L TS, and a 30kw boiler.

@ProDave Where does this stand with de-rating? ( if vertically run in conduit ).

For comparison, the last 500ltr TS with a 46kw DHW coil came in for change of £1150 ish.

For comparison, current job has 3 new connections from the pavement, with 2 cables surface mounted on the front elevation and another brought into the basement flat underground. Nearly £1900 with me doing all private excavation, backfill, drilling and transits, and them just pulling the cables in and mounting the new supply heads. They dug up about a M2 of pavement and Tarmac'd it back in. Half a day's work.

Eg 1 Eg 2 A bit expensive, and I'm not all that convinced with the whole 'tank in tank' necessity TBH. Why not a cheaper straight forward TS?

That's not a crazy amount when you consider what's being done.

Just when you think you've seen everything. Guess that's the final word on the old pineapple chunks being ok to use in them .

Yup, just not as good a dress sense

You'll get 2x 2.5mm T&E's down a 25mm tube without any trouble so why fit two? If the tube is open to the joist voids then I doubt very much if you'd need to consider grouping or insulation factors, with it being so close to the surface and the sockets not being airtight. You'll get a little convection airflow through there too so that'll help keep things at ambient. Oh, and 35mm is a good size in case any are USB.

Pennis. ? Chiselled Adonis was what I meant. Back to roofs we go

What's the detail of the end support for the ridge beam in that first pic? A lot easier than a complex gable . ( Man-shed details still to sort before ordering timber ).

I've been eating facking granola......can even see my feet now ✌️️✌️️✌️️✌️️ Oldest son has even slowed, not stopped, with the jiggling of my man-boobs. ? Ill soon be looking like a Beckham / Pitt hybrid

I too enjoy little better than a ridiculously good surround. Im a bit mutt'n'jeff after 13 years club DJ'ing so I constantly nag SWMBO to turn up the regular tv, and when I've had a tit full of the two crisp packets that flat tv manufacturers call speakers....the guns come out. "The neighbours can hear that" "Yup!"

About right tbh, as they're long trays and low profile eg not a great deal of fall. That will get a little worse as the tray surface gets surface scratches. It's nice and shiny now so the draining is at its best. My bath has falls to the centre plug 'ole and still has water pooling here and there so it's only significant as the tray is in such clear view. Do you look in the bath after the water has drained ? .

Just did That looks really neat, you must be suitably smug ? Only problem now is resisting the urge to sit on the roof in the p155ing down rain to watch the rainwater doing what it should. Would be suitably satisfying though, none the less. .

600mm will allow even the chubbiest cake-lover to get in. That's not a small opening, trust me.

Why the removable panel now? Are you going to hide pies in there ? ??