Unvented hot water heater pipework

[Dave N]

I'm planning to install a small (10 or 15 litre) undersink water heater and am just checking that I can fulfil the requirements for the pressure relie f valve discharge. I expect there will be at least 4.2 metres of 15mm pipe between the nearest cold water outlet and the heater, so an expension vess el shouldn't be needed.

I think I understand the requirements of Part G and have read the unvented water heater FAQ, but since the heater is to be mounted on the floor of a s ingle storey building I'm not sure I can achieve the necessary fall to inst all a tundish and the required pipework. Part G suggests that the tundish needs to be mounted inside the building near the water heater with a minimu m vertical fall of 300mm on the (22mm) outlet pipe before any bends. The h eater will be on the floor and therefore the cold water pipework will only be around 400mm above ground level.

Is the simplest solution to put in a loop of pipe above the pressure relief valve feed to allow for the necessary fall (so the tundish would be above the water heater)? Or would it be acceptable to mount the tundish outside with a vertical discharge pipe?

TIA,

David.

[ARW]

I am pretty sure that you cannot mount the tundish outside.

[Muddymike]

Not being a plumber but being keen to learn I turned to Google to educate myself on what exactly a Tundish is. I am now totally confuse as this is what I found. It seems its a device consisting of goats intestine, sinew and teeth???

"The Tundish folk, originally from the steppes of Tundeland, are well known for their nomadic ways and reclusive culture. so much so that little has been written about their habits and diet.

Crucially important in aswering this question is an appreciation of the difficulties of their diet. The Tundish live almost exclusively on goat products, and only drink goats milk. For years this posed no particular difficulty as they possessed great herds of goats, and grazing was plentiful. But political and agricultural changes have meant that it is no longer so easy for the goats to be grazed all along the course of the nomadic 'way' they follow round the year.

Faced with a choice between abandoning their traditional diet, changing their nomadic route, or innovating, the Tunds determined to do their best to continue in their long-established ways. To do otherwise was to disrupt and, perhaps, destroy their culture. They had long known how to salt and thus preserve goats meat, so the only issue was how to keep goats milk drinkable for long periods.

The solution found to this was both chemical and mechanical. Various additives were found which would ensure that the milk remained drinkable for far longer than normal, provided it was not exposed to air. The Tundish valve solved the problem that presented. It is a device which, when connected to the goatskin container in which the milk is kept, ensures that milk can flow freely out without any air getting in to the bag. The mechanism is an ingenious combination of goats intestine and sinew, stiffened at critical points by goats-teeth pegs.

This piece of ecologically sound technology points a way into the future..."

Mike

[Fredxx]

The very first result might be more helpful.

[Andy Champ]

You're supposed to read the best answer, not the funniest :)

Andy

[Muddymike]

Where's the fun in that?

Mike

[Dave N]

Thanks for all the replies! Yes, mounting the Tundish sounds like an activ ity that we might like to indulge in but I'm not sure if it's legal ;-)

The tundish is an open vessel in the discharge pipe that allows you to see when the system is discharging water, to alert you to a fault. In the end I chose the simple expedient of mounting the discharge pipe straight down a nd out of the building through the suspended floor on to the concrete base (it's a wooden building with the floor raised about 250mm above the base). I would imagine that the worst that could happen is the formation of a poo l of hot water in an inaccessible place that would in the extreme case even tually seep out at the end of the building, by which time the water would b e cool.

Many thanks!

David.