central heating - 15mm plastic pipes?

[sxp842]

hi all

We are getting our hot water tank removed and replaced with a combi boiler. Plumber has recommended a 100-W 30KW Viesmann combi.

We live in a flat which is quite old, the current pipework is about 50 years old, and 2 plumbers have advised that we may be better of replacing the pipework (something to do with higher water pressure of a combi causing a risk of leaks in old copper pipes).

My question is, the plumber has said he will fit 15mm plastic pipes under the floors because it will reduce the number of joints, and he will use copper for the radiator tails. Does this sound reasonable, or would it be better to use 22mm pipes? Or copper pipes?

Property is a second floor 2/3 bed flat (900 sq ft), with 6 radiators and a towel rail, and shower (no bath). I seem to recall plumber mentioning we had a good flow rate, although i can't remember what it is (I can check if it would help?)

Does this sound like it will be ok? I'm happy to pay a bit extra if it will mean we get better quality. I really would just prefer to have radiators that don't take ages to heat up, hot water availble quickly, and good water pressure in the shower. I know combi isn't ideal but due to space we can't really keep the water tank.

I might ask the plumber why he's advising 15mm plastic pipes, but I don't want to make an issue about it if it isn't a big deal.

thanks for your advice

 

[ianmcd]

15mm will be fine

 

[sxp842]

Thanks for the reply. Can I just ask why 15mm would be better in this instance? (If you’re able to explain it in layman terms!)

I’ve just read some things online that suggest 22mm pipes should be used to connect to the boiler and radiators. So I just want to understand why 15mm would be better. Does it depend on the size of the boiler?

I’m also assuming there’s nothing wrong with using plastic pipes?

I’m just trying to understand the pros and cons of different options a bit better as I don’t have any experience of this.

Thanks!

 

[Madrab]

It all depends on numbers/sizes of radiator and the distance the pipework needs to run. He will have to run 22mm from the boiler for a certain distance anyway and then reduce to 15mm. Once that's fitted then using 15mm plastic means he can negotiate around bends and joists under floors etc without having to use fittings.

It should also be cheaper and quicker to install. Just make sure they all heat up correctly before the jobs finished.

 

[OLLIE20]

Copper is a better job than plastic you are correct, if it’s done properly.