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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    I need a funny shaped header tank for a vented system. It will probably have to be long and thin to fit in the space below the ridge of the roof. How feasible is it to build one? I was thinking of asking a fabricator to build a box out of stainless steel. Is it straightforward to make copper connections to the box?

    The other query was insulating it. It should not get too hot, but it would be sensible to have some insulation. I've seen these spray on foam companies. Might this work? Might there be a better solution?

    I'd be grateful for any comments!
    • CommentAuthorgyrogear
    • CommentTimeMar 12th 2017 edited
    How big does it need to be, and how much will it weigh, and how will it be supported ?

    About 200 litres / 250kg / on steel superstructure, probably using a timber stand of some sort.
    • CommentAuthorgyrogear
    • CommentTimeMar 12th 2017
    Maybe you could use a plastic wheelybin with the lid welded in place, and cutouts in one of the sides ?

    240-liter version here...


    Just a thought !

    Nice idea! It would need to be heatproof in case the system overheated, and the space is really limited. A long (2m) cylindrical container would be good, but not quite the ideal shape, and quite expensive. I think the best solution will be to get one made.
    • CommentAuthorskyewright
    • CommentTimeMar 12th 2017 edited
    Posted By: ComeOnPilgrimI need a funny shaped header tank for a vented system. It will probably have to be long and thin to fit in the space below the ridge of the roof.

    Ignoring the DIY aspect, but have you tried a query like "coffin header tank" in a search engine?
    That should bring up links for various long thin pre-built tanks.

    Edit to add: e.g. Trying that and picking a link at random there was a 227 litre tank 1650mm x 460mm x 475 mm (L x W x H).
    Get one welded up by a steel fabricator. IMO stainless steel is not necessary after all radiators are not stainless ! Connections are easy, you just get the fabricator to weld in iron pipe fittings where you want the connections. If you want a ball valve in it then you will need an open top otherwise it can be closed, but must have an open vent hole and either way it should have an overflow (usually led out to a gutter or just poking out of the wall. It must be insulated if it is in an unheated space and either EPS (but think about feeding the mice) or glass wool or what ever else you care to use that might be more expensive but have more eco-bling. If the space beneath the tank is heated then build and insulation box around the tank so as to include the tank in the heated envelope. Don't forget to insulate the pipes up to the tank if the space is unheated.

    Plastic is not a good idea for a header tank because if the heating goes pear shaped then the header tank can go all soft and wobbly and then sag and leak.
    Thanks @skyewright, but I don't think these are going to be the right shape. I think I'll need something that is about 2000 mm long, and a funny shape (see attached).
      20170312 Header Tank.jpg
    Thanks @Peter, that's just what I wanted to hear. What sort of thickness do you think I should specify for the sheet?
    Depends how full you think it will be and if it will have a top. But 2mm should do it otherwise 3mm. Think about the weight of getting it to the location. If it is open top then 2mm if you get some cross supports (ties) between the long sides to stop any bow out. Best advice is probably be guided by what the fabricator is happy to use
    • CommentAuthorgyrogear
    • CommentTimeMar 13th 2017 edited
    Posted By: ComeOnPilgrimI think I'll need something that is about 2000 mm long, and a funny shape (see attached).

    well, you could get *THAT* shape done by a boat-builder !
    (looks just like a ... Water Tank !)

    cf. https://www.google.fr/search?q=water+tank+stainless+sailboat&client=firefox-b&tbm=isch&imgil=Qsccjyo3PHNJDM%253A%253B50x8GbDVHLU2NM%253Bhttps%25253A%25252F%25252Fwww.westmarine.com%25252Fwater-heaters&source=iu&pf=m&fir=Qsccjyo3PHNJDM%253A%252C50x8GbDVHLU2NM%252C_&usg=__iEafKlcWnPRwiyhHueihy00Acgc%3D&biw=1024&bih=641&ved=0ahUKEwjW0NGPqNLSAhWIzRQKHc-eDiQQyjcIKQ&ei=tfPFWJaiH4ibU8-9uqAC#imgrc=ILw9ii2xygz7iM:

    I suspect that for a stainless steel tank you will need a second mortgage !
    • CommentAuthorowlman
    • CommentTimeMar 13th 2017 edited
    Is this a "Feed and Expansion" tank? I had a SS one made for my back boiler it's nowhere near as big. Cold feed at one end and overflow at the other.
    Does anybody know whether the overflow outlet should go directly outside?
    • CommentTimeJul 12th 2017
    It has to go somewhere that it is visible/noticeable. Outside is most normal and conventional because water falling down the outside of a building is noticeable. Mine goes to a tundish alongside the tank and thence to the nearest soil pipe because I didn't want any extra penetrations through my walls, especially not open pipes!
    Thanks @djh, that was exactly what I was thinking!
    • CommentTimeJul 12th 2017
    As long as the tundish is somewhere it can be seen and heard, you should be fine. FWIW, my 'approved' plumber went along with it and signed it off and he then used my site for part of his regular certification appraisal so I'm fairly sure it is kosher.
    • CommentAuthorgoodevans
    • CommentTimeJul 13th 2017
    There is an alternative of having a manual fill header tank (tap nearby and a hose). That negates the need for an overflow but does need regular confirmation of the header tank level (once or twice a year). One advantage is that leaks in the system are detected earlier.
    @goodevans, I was going to have a manual fill, but presumably you also need an overflow for if the tank boils.
    • CommentAuthorgoodevans
    • CommentTimeJul 13th 2017
    Posted By: ComeOnPilgrimbut presumably you also need an overflow for if the tank boils

    No I think not - no extra water - in the event of a runaway boiler the vent pipe from the tank will 'spert' water and steam into the top of the header but as fast as the water goes into the header in will go out of the bottom and back into the system. (it depends how fast the 'steam' from the boiler can get to the header).

    My boiler failed in my last house - lots of gugling and lots of steam in the loft but the overflow did not come into play. Fortunately I was in the house and turned off the system. Whether it is better to have a finite amount of water to boil off or a continuous supply of new water to boil off I'm not sure - If you are not in when this happens you have problems either way. (To boil off 100 litres of water would take a 25KWh boiler about 2.3 hours - that's a lot of steam)

    On the otherhand when the ballcock washer started leaking the constant dripping from the overflow made me fix it (hence why the overflow must be in an inconvenient place)
    • CommentTimeJul 13th 2017
    Posted By: goodevansThere is an alternative of having a manual fill header tank (tap nearby and a hose).

    That was my original plan, but my plumber said such an arrangement was more of a nuisance than a ballcock and I went with his suggestion. It's too early to say whether he was right - we haven't had any problems yet.
    As an update to this, I found a second hand Economy 7 immersion tank on a famous auction site that fitted well. I have an expansion connection, an overflow connection, and added a vent. Plan is to fill it manually as the thought of adding a ball valve did not fill me with joy. On the plus side, I don't have to worry about an overflow (only my plumbing). Thank you all very much for your help! Fingers' crossed for when it goes live.
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