unvented pipe sizings

[crafty]

hi all

just after a bit of advice.

got the nod on a nice little job plumbing up 2 new houses, Conversions.

each is having an unvented (direct) cylinder with two emersion's, there is no other heat source.

my question is, shall i run the main hot feed in 22mm (plastic, its timber framed and access is easy) or 15mm? My instinct is 22 main feed with 22 off to bath then 15 to the rest.

the first appliance from the cylinder will be the bath then the basin and lastly the sink. (thats it only three discharge points).

need i worry about water flow? incoming pressure is fine. i know flow will dramatically reduced from kitchen tap if a bath room tap is used. But thats what you get with a small unvented unit anit it?

any thoughts greatly recived.

crafty 😉

 

[Steve001]

I'd trust your instincts and do the cold supply in 22 and I'd generally do 22 hot feed and branch off in 15 to draw off points even for the bath, being new build conversion def worth checking flow too.

 

[kirkgas]

crafty do you have your unvented ticket? these things can blow up if not properly fitted

 

[Puddle]

Congratulations Crafty,hope jobs goes well !!
Agree with steve,no less than 22mm

 

[Dannypipe]

Yeah steve's on the button.

One thing worth noting, and I'd have to check the book I received when I did my unvented ticket, is that you probably can't run the plastic right up to the cylinder...I seem to remember that within a certain area, all pipe must be copper.

Don't take that as gospel though mate, I'll check my book, but not right now, I'm off to catch Zzzzzz's!

 

[crafty]

great thats what i'll do then, 22 feeds with 15 for draw off points.

kirkgas, no i don't hold an unvented ticket, but i am doing it on the 15th july (booked and paid for, with fast track scheme to get my card asap). These jobs won't be in till the end of july, so will prob my 3 and 4th unvented system.

i have worked allong side plumbers while we fitted unvented cylinders during my training and understand all the principals and saftey controls involved. But i won't be doing any till i'm certificated.

I'm plannig to fit santon premier plus units, can anyone tell me if the TPRV come out in 15 or 22mm? cos i want to know if i will need 22mm after the tundish or 28mm.

 

[Plucky]

discharge size depends on equivalent length <9metres in 22mm <18m in 28mm I think a pulled bend is 0.3m and a 90' is 0.6 (these are off the top of my head so please check in MI)

22mm supply to the cylinders. Nothing says you cant pipe up in plastic except it will look poo and if you value your reputation and want another job out of it you would use copper on show 😉

 

[oldplumber]

tpr valve pipework should be in copper but i think they may have just changed the rules recently to allow plastic if it can withstand the potential heat involved

 

[Gray0689]

Remember the 9mtr rule if over 9mtr the go up a size and take fittings and bends in consideration too

 

[crafty]

no need to worry about 9m's if the dischagre pipe runs to 2.5m (including a couple of elbows) i'll be supprised.

all the pipe work in the boiler rooms will be copper (as per cylinder manufacture' instructions). I'll just go to plastic when it disapears off into the wall. But yes i agree with your suggestion copper will look better. Hopefully i'll get some more work from this developer.