Hot water cylinder vent pipe

[djfox]

Hi,

Please could you help me?

I have an indirect hot water cylinder heated by a back boiler. I have removed the small cold water tank which was positioned directly above the cylinder, and have replaced it with a larger tank in the loft. When I moved the tank I also installed a pump and a power shower which is fed from a Surrey flange at the top of the hot water cylinder. The hot water vent pipe also comes out of the surrey flange and is rooted back to the cold water tank in the loft.

I understand that the vent pipe is supposed to run continually upwards to the cold water tank, however my vent pipe drops below the height of the cylinder and runs under the floor boards of the room, to the next one before it rises verticazlly to the cold water tank. What is the impact of this? I understand that if the boiler overheats the water in the hot water tank, steam will escape through the vent pipe. If the pipe goes down before it goes up, this may make it more difficult to escape, however it will still escape? Is it dangerous?

If it needs to change, is it ok to root the vent pipe directly upwards to a small plastic container which has an overflow through the outside wall directed into my grey water guttering? If so what is the minimum size of that container? The reason for me wanting to do this is that it is a much larger job to route the pipe differently to the loft and there is no way of doing it neatly and unabtrusively.

Thanks

An Engineer trying to learn plumbing diy

 

[Richard C]

I understand that the vent pipe is supposed to run continually upwards to the cold water tank, however my vent pipe drops below the height of the cylinder and runs under the floor boards of the room, to the next one before it rises verticazlly to the cold water tank. What is the impact of this?

Could be quiet serious, a vent pipe is exactly what is says on the tin. Air/steam is natural consequence of heating water & has a serious dislike of going sideways let alone downwards; how on earth do you expect the hw cylinder to vent it's natural build up of air/steam

I understand that if the boiler overheats the water in the hot water tank, steam will escape through the vent pipe. If the pipe goes down before it goes up, this may make it more difficult to escape, however it will still escape? Is it dangerous?

Yes it will make it impossible for air/steam to escape &, as I said above, it is serious; you have also contravined Building Regulations.

If it needs to change, is it ok to root the vent pipe directly upwards to a small plastic container which has an overflow through the outside wall directed into my grey water guttering? If so what is the minimum size of that container? The reason for me wanting to do this is that it is a much larger job to route the pipe differently to the loft and there is no way of doing it neatly and unabtrusively.

Now beggining to think this post is some sort of wind up; very topical for the moment & as a well known tennis player once said, "are you being serious" ! I'm not a plumber by trade but am a qualifed (ex) Professional Engineer & this is all pretty basic stuff in Engineering terms let alone Plumbing. For christ sake & for your own safety, get someone in who knows what they are doing; what sort of Engineer are you anyway?

 

[seco services]

An Engineer trying to learn plumbing diy

and im a scientist

 

[fazedup71]

well i fancy doing a little brain surgery! obviously I don't have a clue what I am doing but am sure I can figure it out on the fly

 

[sooey]

well i fancy doing a little brain surgery! obviously I don't have a clue what I am doing but am sure I can figure it out on the fly

You'll need a bleedin good microscope.

 

[Deleted member 105431]

The reason for me wanting to do this is that it is a much larger job to route the pipe differently to the loft and there is no way of doing it neatly and unabtrusively.

That's what seperates a good heating engineer from a diyer, there IS a way but you don't know how/can't be ar$ed.

 

[Richard C]

well i fancy doing a little brain surgery! obviously I don't have a clue what I am doing but am sure I can figure it out on the fly

You'll need a bleedin good microscope.

Na just a B&D corless, some drill bits & a mobile phone with a consultant on the other end -- seriously it was done only recently

 

[dextrous]

Anyway, back to the ops problem.

One of the main problems with the current vent pipe layout is that it goes up, across and then down. This creates a large section for an airlock - which will prevent steam escaping up and out. Thus it is unsafe and as it is acting as a restriction, is contrary to the regulations.

With regard to you running your own modified vent pipe, it will have to be a minimum of 22mm diameter, insulated for at least the first metre of its run. It must run constantly upwards to it's maximum height. The height of this maximum point must be 150mm plus 40mm per metre of head (this being the difference in height between the water level in the cold water tank and the base of the cylinder) above the water level in your cold water tank.

Your proposed design will mean that the outlet from the pipe is lower than the water tank - this will create a constant flow of water out of the cold water tank, down through the cylinder, back up the vent pipe into your little tank and out into your gutter via this little tank's overflow, which will happen 24-7!

The only way that springs to mind to keep it unobtrusive would be to use a coil of 22mm plastic pipe which can be fed up and through the eaves of the house to overflow back into the cold water tank, with the top of the loop being set as described above. This will require the pipe to be insulated for it's whole length. It is thus feasible.

 

[sooey]

well i fancy doing a little brain surgery! obviously I don't have a clue what I am doing but am sure I can figure it out on the fly

You'll need a bleedin good microscope.

Na just a B&D corless, some drill bits & a mobile phone with a consultant on the other end -- seriously it was done only recently

Brain....Fly...Surg....ahh ferget it.

 

[sooey]

Just to be a pedantic smartarze it should be 150mm plus 40mm per metre of head.

 

[dextrous]

Just to be a pedantic smartarze it should be 150mm plus 40mm per metre of head.

That's what I said!

 

[dextrous]

Anyway, op, thanks for showing an interest in your own thread. It's nice to see you appreciate our prompt replies!

 

[djfox]

Thanks for your help,

I've just switched off the system, awaitng plumbing quotes. I don't think i'll be diying again!!

 

[dextrous]

Thanks for your help,

I've just switched off the system, awaitng plumbing quotes. I don't think i'll be diying again!!

Don't give up so easily. Assuming that other hot water outlets (i.e. taps) take their supply from the existing vent pipe, you only need to install a compression tee just above the surrey flange, connect the existing vent pipe to this after a bit of an adjustment, cap this vent pipe immediately after the tee which feeds the other taps (to prevent a deadleg of pipe).

Use an offcut of this now obsolete 22mm vent pipe to run it up the wall where you were going to run it in your original proposed route, before using a compression fitting close to the ceiling to connect to some flexible plastic pipe which will run along the eave before getting to the cold water tank. This is easy, and since you have done some pipework already, well within your capabilities.

 

[BingoBongo]

well i fancy doing a little brain surgery! obviously I don't have a clue what I am doing but am sure I can figure it out on the fly

you could always have a go, then when you **** it right up see if there is a forum to help you fix it