My central heating header tank did not have a lid (the builders missed it off for some reason). I've made a replacement lid from marine ply and covered with polythene. It fits snugly apart from the hole I've had to make in the top for the vent pipe to enter. I'd prefer to have this pipe enter from the side of the tank above the water level (so that there is no need for a hole in the lid). Is such an arrangement permitted by building regulations?
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Question about central heating vent pipe
- Thread starter jonc123
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Not a plumber, and I am sure one will be along, but hot water expands so is lighter than cold water, so there is a distance between water level and vent pipe, or it would circulate.
I understand that and my intention is that the vent pipe would enter the tank (horizontally) above the water level and remain above the water level. My question is whether this is permissible - or must the expansion pipe enter via the lid (vertically)?
Unless it was combined then IIRC the min design spec used to be 450mm from the top of the curve over to the water level but I'd need to check.
1. Agree with Madrab. 450 mm from top of curve to water level. This height will absorb the expansion of water for average sized systems (4% of system water volume) without disturbing the contents of the F&E tank.
2. If it goes in horizontally:
2.1 Water will expand into the tank, the water in the tank will then absorb more oxygen from the air and could exacerbate internal corrosion of radiators.
2.2 There may be a risk of water splashing against the side of the tank and perhaps spilling past the lid. For example, if the system pumps over for some reason.
3. You could look at the possibility of changing to a combined feed and vent system, but this would require increasing the size of the feed pipe.
2. If it goes in horizontally:
2.1 Water will expand into the tank, the water in the tank will then absorb more oxygen from the air and could exacerbate internal corrosion of radiators.
2.2 There may be a risk of water splashing against the side of the tank and perhaps spilling past the lid. For example, if the system pumps over for some reason.
3. You could look at the possibility of changing to a combined feed and vent system, but this would require increasing the size of the feed pipe.
Yes, but it's not to absorb the expansion, 4% is 4 litre on a typical 100 litre system, giving about 30mm rise in the F/E tank. The 450mm is to exceed the pressure loss between the open vent and cold feed connections (with a margin) to avoid pumpover out of the vent pipe.
I suppose the vent pipe could go in the tank side, if the connection is well above the water surface. But if the vent pipework is existing, it would need rerouting, which I don't think is worth the effort.
That's the same with the vent in the top or the side.
If it pumps over it needs fixing asap. Splashing against the lid is the least of the concerns!
No, it would not work adequately as a vent pipe. It needs to rise up, several inches above the tank, over, then down through the top cover, but end well above the water level.
1. Looks OK to me except that:
1.1 The vent inlet would need to be an appropriate distance below the overflow level.
1.2 You would need some way to let air into / out of the tank to cope with changing air pressure as the tank empties / fills.
1.1 The vent inlet would need to be an appropriate distance below the overflow level.
1.2 You would need some way to let air into / out of the tank to cope with changing air pressure as the tank empties / fills.
Wouldn't the vent inlet be better above the overflow level?
The lid isn't hermetically sealed - so air ingress should be OK. Also air can enter via the overflow pipe.
Is a 25mm hole in the lid really that much of an issue though?
Just needs a bit of exterior paint or marine varnish then - no need for polythene?
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