Spec for platform to raise cold water cistern

[HouseUpgrade]

I'm planning on replacing the current HW cylinder on the 1st floor with a new one in the loft so that we still have a decent HW store, and building a platform about 1200mm above the loft floor to raise the current CW cistern and place the HW below it.

I'm OK with the plumbing and electrical side of this, but am less sure what size and arrangement of timbers would be needed to prevent the embarassment of about a half-tonne of wood and water coming through the ceiling .

The general plan is to spread the load on three parallel 4x2" bearers over the house's centre wall plus 6 joists on each side of that wall (so 12 joists in total) to make a base platform. Rising form this a frame of supporting vertical timbers with a further platform on top.

Initial thinking for the sides is to use 1200mm 4x2" lengths on end cross-braced with single length of 6x1" on each diagonal (so two lengths per side) and held together with M8 coach bolts and timber connectors, then 3x2" around the top edges to take the upper platform (possibly hang a third length across the centre using mini-hangers).

Does anyone knbow if that is a typical spec for making up this type of frame, or what is standard?

I've thought about taking the verticals up to the roof rafters, not so much to provide any direct load bearing but to help prevent any move away from the vertical. Any merit in doing that?

TIA

 

[tamz]

A bit over spec but it will be fine.

 

[dextrous]

As you are replacing the cylinder, I take it you've lookied into pressurised cylinders (so you get hot water at mains pressure) etc, althought thse do need G3 qualified plumbers to install.

In any case, would a combination cylinder not be easier to deal with as it has the header tank and all connecting pipework inbuilt.

 

[HouseUpgrade]

A bit over spec but it will be fine.

Thanks. Good to know it doesn't need more than that.

Any thoughts on what would be 'normal'? The less I use the less additional weight I'm adding.

 

[HouseUpgrade]

As you are replacing the cylinder, I take it you've lookied into pressurised cylinders (so you get hot water at mains pressure) etc, althought thse do need G3 qualified plumbers to install.

Thanks for suggesting it.

Thought about it, but decided against due to the BR and certification issues. Also not sure that mains pressure HW is needed: decent gravity flow will hopefully be enough.

In any case, would a combination cylinder not be easier to deal with as it has the header tank and all connecting pipework inbuilt.

Resaons for passing on a combi: unlikely to give a decent flow rate to the two simultaneous showers that we anticipate having in a couple of years as the kids get older; I plan to fit a dual-coil cylinder to allow for solar or wood burner DHW heating if appropriate in the future; a number of friends have suffered from "no combi = no heat' issues recently so I much prefer the electical backup that an immersion provides; one of the plumbers who came to quote for some other work and lives nearby was grumbling that the water company had recently reduce his water pressure making his recently fitted combi a bit of a whire elephant (and fully supporting the idea of a traditional system).

Will probably go for a system boiler though to eliminate the F+E tank.

 

[dextrous]

Think you may be getting confused with a combination boiler and a combination tank

 

[HouseUpgrade]

http://www.toolstation.com/shop/Heating/Tanks+Vessels/Indirect+Combination+Tank+1200450/d230/sd3234/p46323

Thanks again

But unless the whole cylinder is raised you still don't get the pressure, and themostatic valves like balanced pressure so a shared CW source is good for that.

Also may end up with a low-ish pressure shower pump and I'm not sure that they would play nicely with the combination cylinder as the feed to the loft is slow at present (which may improve when when the steel feed pipework is replaced) so the mini-tank might run empty.

 

[HouseUpgrade]

Think you may be getting confused with a combination boiler and a combination tank

Yep, confused by misreading it .

 

[dextrous]

But unless the whole cylinder is raised you still don't get the pressure,

Not true - the only thing that matters is the height of the cold water tank. The hot water cylinder's position is of negligible effect.

Also may end up with a low-ish pressure shower pump and I'm not sure that they would play nicely with the combination cylinder as the feed to the loft is slow at present (which may improve when when the steel feed pipework is replaced) so the mini-tank might run empty.

Fair enough.

 

[HouseUpgrade]

But unless the whole cylinder is raised you still don't get the pressure,

Not true - the only thing that matters is the height of the cold water tank. The hot water cylinder's position is of negligible effect.

That's interesting. Firstly (having never seen one) I'm assuming here that the combi-cylinder is fed from the mains supply with its own valve into a 'private' vented mini-header tank. Am I misunderstanding that?

Are you saying that it never matters where the combi-cylinder is (and that the HW pressure doesn't matter), or that it will typically be next to the CW cistern to they will tend to have similar pressure?

If we've managed to confuse each other and you're saying that with a conventional HW cylinder then the location of that cylinder doesn't matter then I think we're just agreeing that raising the CW cistern is a good thing. The reason for moving the HW cylinder to the loft is not to raise it as such, but to make space in the bathroom. This then leads to to the CW cistern being raised, which happens to give more pressure.

 

[tamz]

Combination cylinder

http://www.plumbingpages.com/featurepages/HWcombination.cfm

Only supplies hot and is fitted high up, usually loft. Not suitable to pump from because of small size of integral cold tank.

With a conventional cylinder it doesn't matter where it is fitted in relation to the CWS. (below obviously)
It will have little bearing on pressure.

If you are positioning the cylinder immediately below the CWS make sure you use a 28mm feed or you will have air problems. The water will be drawn from the cylinder faster than it can be replaced so it will draw air down the expansion.

With regards to your tank stool, spanning over 4 joists is usually sufficient. Water weighs 1kg /litre (10lb/gallon).