Plastic pipe sizing for new DIY CH system

[Papajimmy]

I've tried a search through the forums and wiki and I'm sure this is an on-going subject. the question is, does the plastic pipe inserts reduce the flow and return from the radiators substantially. I was told by the pipe supplier in the store and also by a heating engineer that I can use 15mm plastic all the way through, teeing off for the flow and return in 15mm also. That would be an easier install as its concrete floors and I'm having to be creative to lose the pipe work. My BIG concern is when you fit the Tee connector I think it will reduce the flow because the ID of the tee is probably less than 10mm. Does anybody have any experience either way. I'm buying the pipe soon so that I can get other works done , any constructive comments appreciated. sorry for the ramble.

 

[Jackrae]

Hep2O do stainless steel inserts that are very thin walled so might better suit your purpose. Some of the plastic inserts are quite thick

 

[Papajimmy]

Thanks Jackrae, any thoughts on using 15mm throughout, that's on flow, return and tee offs to and from rads. 22mm is an option but harder to fix pipes behind extended skirting etc.

 

[kbdiy]

The problem with using 15mm as I see it, is what happens if/when you are dissatisfied with the heat output when it's all done? I know the experts on here will have various formulae that can be used to calculate output more precisely but I would go for 22mm all the way to be on the safe side.

Better to take the pain now rather than be unhappy when it's all finished.

 

[jazzcricket]

15mm will be fine,the restriction on flow is negligible.
I presume its a fully pumped system?
Heat output will be guided by the size of the boiler. You need to work out what size radiator you require in each room.
B and Q website do a very simple calculator you can use, just input size of room,etc.
Any more questions just ask.

 

[Papajimmy]

Thanks Jazzcricket, that is reassuring. its only a small 2 bed flat with 6 medium size P+ off the one loop flow and return and one rad on its own flow and return going the other way. The system is fully pumped and Ive been recommended the potterton 33 HE as part of the deal, so probably a bit over sized??. should be a breeze in 15mm plastic and when I took off the skirtings there is a pocket where I've removed timber batten that held the skirting on. I've fixed some edge insulation like you'd use on underfloor heating to minimise heat loss into the external walls. I just had this nagging doubt about restriction of the pipe inserts into 15mm, then going through the Tee connector. Cheers.

 

[jazzcricket]

yeah i would say 33kw is overkill for a flat definitely.
Although always better to be oversized, rather than undersized.

Good luck, should be straightforward enough.

 

[Papajimmy]

Thanks, always good to get reassurance before I fork out my hard earned.