Sorry, another DIY question....

I am in the process of trying to rejig the hot water cylinder...

Because it is very close to the roof, I cant easily have a vent pipe comming straight out of the top of the tank and going straight up to the header tank...

What effect would it have on the hot water system if the pipe comes out of the top of the hot water cylinder, drops 10" and then goes off sideways before being T'd off for supply and vent

Like this:



And what is the general rule on using plastic pipework for cylinder plumbing? Is it acceptable?

You have a potential air lock issue there, air does not like to flow downwards through water pipes! Could you not Tee the vent into the second right angle fitting after the tank?

that wont work.
You need it to be able to vent straight up from the cylinder, but not to the header tank. Needs to vent over main Cold water tank.
As above, put a tee into the 2nd right angle with a slight rise off the cylinder to it.
And dont use plastic, not good stuff to use at all.
hope it helps

That is your main cold water tank, you only have the one over your hot tank for the header and possibly another for your CH system. You can run the vent pipe straight up with a tee in it and tale off anywhere for the kitchen or bathroom they don't have to come off separate near the tank. Think the route out to use the least pipe and unions possible. I use solder fittings or compression joints as I don't trust plastic. There will also be an overflow from your header tank to somewhere outside usually over the door so you can't ignore it.

header tank

[Edited on 12/8/09 by Peteff]

There's nothing wrong with plastic, I use it all the time for threading through floor voids and in the roof area. I dont use it where it can be seen and it shouldnt be used anywhere near a boiler, think 1m is as near as you can run it.

Personally I wouldnt use it in this instance for various reasons, also remember that the minimum distance from the centre of the cylinder to the T off to the vent and distribution pipe is 450mm.

Hmmm.. thanks for the input all.... Looks like the design of the currant system is worse than I had feared.. Looks like I have to make quite a few changes to make it "work"...