Vent pipe size for vented cylinder installed in 2005-6

[jimjamyaha]

Hey, having searched this forum and last building regs (2000) from around that time...

Any idea what the correct size is for a vent pipe for a vented hot water cylinder, gravity fed? I.e. the one that is continuously rising back up to the cold water feed tank for the cylinder?

Have discovered it's 15mm, but can only find reference to 22mm but this is in building regs 2010 onwards.

 

[ShaunCorbs]

22mm

 

[jimjamyaha]

Ok, thanks. Have figured it out..... Whole dhw output seems to be combined with the vent pipe... Ie this tees off at the top of the supply and does so in 15mm.

Is it "normal" to have a combined flow and vent?

Setup is dhw cylinder at lowest level. Feed tank in attic. All outlets between these.

 

[ShaunCorbs]

Depends on cylinder location but the vent should be always rising and straight off the distro pipework and should be in 22mm pipe as it’s gravity

 

[Last Plumber]

In my book it should not be less than 3/4" bore. It should rise from the outlet all the way to the tank/cistern that feeds it.
There should be no valves throughout its length/route. It should rise and fall over the tank (think umbrella handle) enough to prevent water being ejected out of it.

 

[jimjamyaha]

Thanks all... So I guess it's a bit of a stretch, but it's continually rising, but also has the hot water supply pipes off it.

Otherwise apart from it being combined and also that the final stretch is in 15mm it's good enough. But another classic British gas install 🤭🤡

Thanks for your insights, all.

 

[Ben-gee]

The hot supply outlets should not tee off the vent, you will get problems with airlocks.