Replacement cold water tank

[Grenage]

Good morning!

One inlet would be easier; I just wondered if the old tank might have a little stagnation at the top with the water entering and leaving at the bottom - the tanks would also refill quicker. Happy to go with the advice of just one inlet though, if you think it's better.

Good call on the isolator between tanks; hadn't considered that.

Russell.

 

[Madrab]

The tank is approximately 70w x 53d x 50h

At those dimensions it sounds like you have a 25Gal cistern, so another of the same size would give you approx 50gal, which would normally be large enough to give a reasonable system supply. The weight will be the same across the rafters though. Nice thick WBP plywood to spread the load and it should be fine unless you have really small rafters, if so then you may need to sister them up.

If you are wishing to tandem the cisterns then you would pipe them together using 22mm pipe and feed the hot and cold circuits from the cistern without the fill valve. This allows the water to circulate through the primary fill cistern to the secondary supply cistern keeping the flow and circulation constant avoiding stagnation. A proper bylaw kit on each cistern would also help.

TBH I wouldn't see why you would want to put a valve in between, you would normally have a full bore valve on each outlet to isolate each supply if servicing is needed.

 

[JohnD]

A bath can take about 100 litres of water, which is about 45 gallons, and this is likely to be the biggest/fastest load on your tank(s). If your tank is slow to refill then your 50 gallon total is as small as I think you can reasonably go.

 

[bernardgreen]

if the old tank might have a little stagnation at the top with the water entering and leaving at the bottom

 

[JimCrow]

View attachment 164424

 

[bernardgreen]

My original sketch was not well drawn, the feed to the second cistern was drawn too high.

Joined at the bottom does have the slight (?) disadvantage that the surface and upper layers of the water in the second cistern are not agitated when water is drawn. This could result in a layer of "crud" developing on the undisturbed surface.

WRAS give advice https://www.wras.co.uk/downloads/public_area/publications/general/information_note_guidance_for_connecting_storage_cisterns.pdf

 

[Madrab]

The alternative method, usually used in larger 75+ gal systems would be to have both cisterns mains supplied via 22mm on a delayed float valve and then 1 28mm distribution pipe from each cistern joined together in a header/manifold arrangement with 22mm system supply pipes branched from the manifold to each required circuit.

 

[Grenage]

Thanks guys, I really appreciate your input.

Would I be mad to consider adding a 50 to the 25, if I measure the joists and try to calculate their load tolerance?

I'm just thinking that at 50gal and let's say a power shower rate of 18l/m (worst case), that's only 10 minutes in the shower.

 

[JohnD]

View attachment 164427

'mmmm, water that flows uphill.

Where can I get some of that?

 

[JimCrow]

My original sketch was not well drawn, the feed to the second cistern was drawn too high.
View attachment 164427

Joined at the bottom does have the slight (?) disadvantage that the surface and upper layers of the water in the second cistern are not agitated when water is drawn. This could result in a layer of "crud" developing on the undisturbed surface.

WRAS give advice https://www.wras.co.uk/downloads/public_area/publications/general/information_note_guidance_for_connecting_storage_cisterns.pdf

WRAS are to do with FITTINGS bernard not Water Bylaws.

 

[Grenage]

Ok I had a proper look at the joists, they're all 2x4 at 14.5-15.5 inch centres.

I was wrong about there being no wall available, it's there but the joists around it have been cut out. Cross-pieces of 2x4 are secured between the joists either side and across the wall.

View media item 102836
The wall is to the right of the piece of wood, in the centre going away from the camera.

I'm assuming that there was maybe a tank there before, although I don't know why they'd remove the joist. Also no idea why the new tank didn't go in its place.

Any reason a cylindrical 100 gal couldn't go there? Figure it's not ideal with the joists gone. Otherwise maybe one of those long 100 gal coffin tanks would spread the load. Being so shallow I assume you don't get the full benefit.

 

[JimCrow]

A coffin tank and 2 lengths of 6"x2" on edge to span 6 of the ceiling joists then plywood on top for the tank base to sit on, the closer to the wall the better.

 

[Madrab]

100gal (450 litres) is nearly half a ton, I'd check any cut joists very carefully to ensure they can carry that weight happily. The current cistern to right sits on batons that are resting on top of the main spreader beam whereas those thinner ceiling batons in the forefront are sitting in hangers nailed into the side of it. You will need to spread the weight over to the main spreader to the left too I'd reckon.

 

[Grenage]

Cheers, I did wonder about that. Maybe there was some water damage to that area and the joists were rotten in the past; I'll never know.

I suppose I should ignore that area, put a coffin tank behind where the old tank is as close to the external wall as possible. As JimCrow suggests, two or three 6x2 across plenty of joists then some 18mm/24mm ply across the top.

 

[JohnD]

100 gal

Did you mean 100 gallon? That's about 4 baths. I have a 50 gall which is pretty big. Do you have several bathrooms?

Vented hot water cylinders are often in the region of 100 litres, which is about one bath.