Length of vent pipe

[spaced1]

hi i am adding a radiator to my loft conversion ,i know the central heating expansion tank has to be higher than the rad but how long can the vent pipe be from the hot water tank to the expansion tank and can it have a couple of bends in it . Thanks

 

[Watchmaker]

I suppose, theoretically, the vent pipe can be as long as you want it. After all, it does just that, ie "vent". However, it must not be too short as, instead of circulating water, through the heating circuit, the pump would tend to "pump over" into the expansion tank. I cannot see that a couple of bends should affect it's function and it's ability to operate safely unless, of course, they are tight, ie, elbows, which would affect it's safe operation. When I installed my highest radiator, into the loft conversion, I experimented with the circulating pump settings, ie, turned the pump up to a high setting so that it did pump over into the expansion tank, and then reduced it's "head" to just give a good "head" for supplying the highest radiator. If you can get the expansion tank as high as possible, above the new radiator, so much the better. My system has worked well for a number of years, with the vent pipe, from the bathroom airing cupboard sited cylinder, extended up to the expansion tank,at a high point in the loft conversion above it.
These comments are from a DIYer and, hopefully, others will comment with more advice.

 

[Deleted member 105431]

If your boilers suitable I'd recommend conversion to a sealed system and remove the tank completely.

 

[muggles]

The open vent can be as long as it can be, it's not a problem. Nor are putting bends in particularly, although it is better to use formed bends than joints if possible. What is important is the height of the bend above the header tank. This should be calculated at 150mm+30mm per metre head of water. You find out how many metres head you have by measuring the vertical distance from the waterline in the header tank to the base of the hot water cylinder.

 

[muggles]

If your boilers suitable I'd recommend conversion to a sealed system and remove the tank completely.

I suspect he's looking to do the work himself, this is something that should really be left to the pro's

 

[liverpoolboy]

muggles - the vent pipe should terminate higher than the "water level in the cistern) 150mm + 40mm per metre minimum.

Also you need at least 1 METRE from the f & e cistern water level to the highest part of the system (usually the primery flow to the hot water cylinder).

and divide the pump head (eg usually 5 metres) by 3, so just over 1.5 metres, and this is the diatnce (minimum) that should be from the pump to the f & e cistern water level.