I was googling for a new cold water storage tank for the loft, and started reading about the tragic consequences of faulty immersion stats in hot water cylinders filling cold water tanks with boiling water via the vent pipe. Which made me think why feed the safety vent back into the tank in the first place? In most systems, designers strive to eliminate runaway feedback loops like this. The safety vents on hot water cylinders and boilers are only needed when fault conditions produce boiling water, and surely you do not want it recirculated, you want it out of the system and replaced with cold water. Is there a good reason why, with precautions against scalding, the safety vents should not discharge externally?
Why put vent pipes over tanks?
- Thread starter bobj2a
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Many years ago when most houses had a solid fuel back boiler, it was common practice for the lead vent pipe to discharge onto the roof.
Also, correctly installed, the cisterns shouldn't have caused the deaths.
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that wouldn`t last long with the Travelling roofers about . Probably iron Indeed - not over bedrooms , possibly over a/cupd. or landing - no so easy with a trussed roof though
They'd be liable to contamination, freezing, blockage or theft outside.
A poster on another forum reported that they were commonly terminated outside in Scotland.
Inside they terminate inside a clean, sealed tank.
It is very unusual for the water to actually boil, even rarer now since new thermostats were modified after those two incidents and a manual reset overheat thermostat was added.
The tanks would have withstood the boiling water if they'd been installed correctly.
Most people would have noticed their water cylinder boiling and would have switched it off.
A poster on another forum reported that they were commonly terminated outside in Scotland.
Inside they terminate inside a clean, sealed tank.
It is very unusual for the water to actually boil, even rarer now since new thermostats were modified after those two incidents and a manual reset overheat thermostat was added.
The tanks would have withstood the boiling water if they'd been installed correctly.
Most people would have noticed their water cylinder boiling and would have switched it off.
Any open pipes or ducts are liable to contamination if terminated outside.
http://i.imgur.com/caEpBHW.jpg
I'll stick with the indoor version.
http://i.imgur.com/caEpBHW.jpg
I'll stick with the indoor version.
Yes, I have always put them over the tank in the traditional manner without really thinking about it, but I’m not so sure that it’s a good idea. Granted, the cisterns in question were not properly supported, and there must be a good few of those about, but there were a number of factors involved, and venting boiling water back into the tank was a major one. For sure, nothing is foolproof, but do you really want a safety system that makes the problem worse?
According to CIPHE the hot water vent should not terminate over a CWSC used for wholesome water. So where should it go?
According to CIPHE the hot water vent should not terminate over a CWSC used for wholesome water. So where should it go?
No help at all, but a pub I once knew well had a coke burning CH stove with no controls except a damper with the vent discharging into the ladies toilet cubicle WC high level cistern.Regulars knew which cubicle. It was a great laugh when somebody came out in a cloud of steam screaming and soaked.
Guess nowadays somebody would ban it.
Guess nowadays somebody would ban it.
Educated guess; over the feed and expansion tank for the heating.
Cws cistern doesn't contain wholesome water.
Well it most certainly can. And if it’s used for cleaning your teeth DEFRA recommend that it does. But I sense thread drift into the murky depths of wholesome water.
Venting over the F&E has appeal, but it is likely to be spilling hot water from the overflow fairly quickly.
We already have exterior discharge of boiling water from UV systems, so why not from vented?
UV discharge pipes don't contain water unless there is a fault. They are also open to atmosphere at both ends and not a body of domestic water.
Sorry Dan, I’m not following your drift here. Fault conditions is what the thread is about. And the advisability, when in fault mode, of the hot water cylinder discharging back into its own cold water supply. Whatever may be said about the cisterns not being properly supported and people should have noticed what was happening, the fact remains that this is an inherently unstable arrangement and the deaths would not have occurred if the vent pipe had discharged elsewhere. Other systems, in fault conditions, do safely discharge to the exterior.
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