Pipe inserts: Do I need larger diameter pipe if I use them?

[tommcdonna]

In a scenario when I would usually use 15mm copper pipe, what size plastic pipe should I use?

Obviously 15mm plastic with an insert added, is going to have a smaller internal diameter (at the joint, but it will still restrict flow) than 15mm copper with no insert.

By that logic I should use 22mm plastic with insert where I would normally use 15mm copper?

 

[seco services]

what are you using it on ?

 

[crockett]

Depends what end result you are after. 15mm plastic pipe is fine for direct replacement, unless you are running hundreds of metres of the stuff and pressure tolerances are critical. What are you attempting, or planning ?

 

[Corgigrouch]

But where you would have tight soldered elbows on copper, you would have wide smooth curves in plastic... Assuming that you use it as is intended..... what do you intend to use the pipe for, water or heating?

 

[tommcdonna]

Yep, should have been clearer.

The pipes will be for the radiator circuit of a pumped central heating system (3 bed semi, 8 rads).

I'm tempted to run pipes in 22mm plastic for the under the floorboards part and 15mm copper up/down to the rads (the visible pipes). Is that overkill and would it be easier / cheaper / with negligible performance difference just using 15mm throughout?

 

[crockett]

Then 15mm will be fine as a direct replacement, and 22mm for replacement of 22mm copper. If on central heating I would use copper tails from the rads to join under the floor with plastic, and avoid using plastic at least a metre from the boiler flow and return