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Discuss Why are Cylinders rarely in the loft for Trad. Gravity Vented Systems? in the Central Heating Forum area at

  1. GasAt300Bar

    GasAt300Bar Member

    Sorry if I come at this form the wrong direction. I'd like to move my vented-cylinder into the loft. I run two shower-pumps too. I realise a sealed-cylinder is the easy route. Sadly I've not got much mains pressure. Combination boilers don't really have the grunt for fire-hose showers.

    I'm hoping it's as simple as buying a vented combination HW cylinder as tall as I can find space for. Then site it as high as possible.

    Both with a good wall to sit on, I'd like to site the cylinder in one of two places. Loft height is the issue:

    Site A: 8ft of space but right in the midst of the loft, space I want for a loft-conversion.
    Site B: 4'6" in a gable-end (out of the way)

    Out of the way is B favourite, but minded to trad. systems usually having HW cylinder and CW tank on different levels I question the headroom, at 4'6" in the gable-end.

    Minded to shower-pumps, two questions.

    1) I realise the CW + F&E traditinally goes far above the waterline of the HW tank, but not why? Do CW + F&E tanks really need to go far above the HW tank? Even back in the day, if the height and insulation is there, why did yesterday's plumbers not put the lot up in the loft?
    2) Can I move my vented HW tank to Site B: 4'6" in a gable-end (out of the way).

    Last edited: Dec 6, 2018 at 4:58 PM
  2. gmartine

    gmartine GSR

    Besides siting 100's litres of hot water above your head its not very convenient, think about sealing your CH system to save having to install an F & E tank.
    • Agree Agree x 1
  3. Gasmk1

    Gasmk1 GSR

    Because you will have virtually no head as most loft are low so the cylinder was sited in a cupboard normally in a bedroom with the tank in the loft sometimes lifted up on a still to give a decent head of water.
    • Agree Agree x 2
    • Disagree Disagree x 1
    Last edited: Dec 6, 2018 at 5:41 PM
  4. snowhead

    snowhead Well-Known Member

    2 further reasons,
    The further the Hot cylinder is from the point of use the greater the dead leg of water is.
    That means more wasted water and more energy wasted heating up the new dead leg of water.
    Depending on which yesterday you want to use, houses generally didn't have central heating, tumble driers didn't exist, rooms were cold and damp so the airing cupboard was an essential.
    You couldn't have an airing cupboard in the loft..
    • Agree Agree x 1
  5. Mark K

    Mark K New Member

    The head at the tap is created by how far the cold water tank is above it, the hot water cylinder is, effectively a bulge in the pipe where water is heated. My HW cylinder is in the loft, with the bottom of the cold water tank just above (about 12") the top of the HW cylinder.

    As long as the CW tank is above the top of the HW cylinder (or more correctly, the flow pipe), then water will flow into the bottom of the HW cylinder and out of the top and you will have, more or less except for pipe restrictions, the same pressure at the taps as the CW from the tank.

    Where you site this in order to create space for other things is for you to decide.

    I did this because the house I moved into was too small at the time to waste space on an airing cupboard. I run 2 pumped showers from a separate connection in the HW cylinder and 2 baths as well as the kitchen etc and have never had a flow problem with washing machine or dishwasher on while showering etc, except when the cylinder scaled up so that nothing could flow through it, but that's another story.

    I suspect the reasoning behind originally putting the cylinder in the house is one of insulation before pre-insulated cylinders became the norm.

    Just my opinion and experience.
    • Like Like x 1
    • Agree Agree x 1
  6. chris watkins

    chris watkins Plumber

    Not sure you quite understand the main issue here, the system you are proposing to install is a traditional Gravity one i.e. the cold water storage cistern has to be above the hot water cylinder as the water flows between them by gravity (& then on to the taps or booster pumps).
    The "grunt" for fire-hose showers suggests a cold water storage of at least 100 gals with a large hot water storage to boot. The cistern needs 350mm clear space above it so even using a horizontal hot water cylinder you are not going to have a loft space left.
    and what sort of base are you going to construct to support the cistern, there is a lot of weight going up in a structure that was not originally designed for it ?
    • Agree Agree x 5
    Last edited: Dec 6, 2018 at 6:14 PM
  7. GasAt300Bar

    GasAt300Bar Member

    Thanks all. I’m getting abetter grip o f this:

    1) I can see pre-tumble dryers, you wanted an airing cupboard.
    2) The dead-leg will still be a pain but liveable.

    3) Quote:

    The tank is a bulge in a pipe. My HW cylinder is in the loft, with the bottom of the cold water tank just above (about 12") the top of the HW cylinder.

    Yes, that is how I had it. Put the bulge in a pipe where we like. The head doesn’t change. You run 2 x pumps via separate connection. Exactly the set-up I’m after.

    For ‘grunt’ I realise I need stonking great tanks with all the weight problems that come with them. I have an RSJ if need be.

    Chris Watkins says

    The cistern needs 350mm clear space above it so even using a horizontal hot water cylinder you are not going to have a loft space left.

    Is this 350mm a regs thing? This could be the killer. Why do we need 350mm of air above a tank? 350mm for both CW + F&E?
    Last edited: Dec 6, 2018 at 6:36 PM
  8. chris watkins

    chris watkins Plumber

    It is possible, here's one I installed when I was 18. (not the wood work that was me dad's handy work).
    The problem is if you want to put the pumps up there as well, the suction they can create can pull air in via the open vent. 2008_0705Nans0021.JPG
    • Like Like x 1
  9. Ric2013

    Ric2013 Plumber Top Contributor!!

    350mm is access for maintenance. It is a law (though I had remembered it as 300mm for some reason). Also the hot water needs to reach taps in less than 30 seconds. That is also the law. Both in Water Regulations.
    To be honest, a power shower and combination cylinder sounds like the wrong idea. If you want a power shower off a vented cylinder, a separate cistern and cylinder is a much better plan.
    • Agree Agree x 2
  10. chris watkins

    chris watkins Plumber

    Water Regs 1990 - G16. 14a: Minimum unobstructed space for cisterns up to 1,000L. Need space to maintain the float valve & inspect / clean cistern.
    • Agree Agree x 1
    Last edited: Dec 6, 2018 at 6:58 PM
  11. GasAt300Bar

    GasAt300Bar Member

    300mm or 350mm, neither will fly. So I 'm into the more roomy section of the loft. With CW's Dad's design or similar. I realsie I will have head problems feeding shower-pumps, but that is doable. Works now , where they are. This move increases the pump-head.

    I cited combination cylinders as an example of what I had in mind. I've not seen any that will have the 'grunt'. I'll need the existing moved upwards.

    30 secs to hot? I understand you can get return-loop pumps. Is this a work-round?
  12. Ric2013

    Ric2013 Plumber Top Contributor!!

    One more problem with cylinder in loft: if there is very low head between the cistern and cylinder, is there not a risk of dragging air down the vent when the pump runs as the flow into the cylinder from the cistern may not keep up with the flow from the pump?
    • Agree Agree x 1
  13. GasAt300Bar

    GasAt300Bar Member

    So it's twinned 22mm to everything. And Essex Flanges etc.
    Currently the highest pump sits midpoint to the HW tank. It's fine. Moved upward will be good.
  14. quality

    quality Plumber GSR

    Shower pumps in my experience (which is small) are poor. Combi never in a million years. Storage Combi possibly but not in a loft. Unvented system yes. It will perform and be more effective than most other options
    • Agree Agree x 1
  15. GasAt300Bar

    GasAt300Bar Member

    That is a killer. With that requirement I'd need a horizontal cylinder.
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