Loft water tank size

[robgraham]

I'll start off by saying please DO NOT reply saying rip it all out and fit a combi, because that just isn't going to happen.

This is not an emergency yet but by fortunate chance I've just spotted that the steel water tank I currently have has a very low frequency drip from a corrosion point. Bucket is now in place - not that that will help much if it goes through in a oner mind you !

There are height and possible weight constraints on where I can fit the tan k. My problem is that the current tank is 35 gallons and so far all the lo ft tanks I can find are either 25 or 50 gallons. A 25 gallon tank will go in fairly easily - 50 gallon one will add 150lb to the structure and be sig nificantly more of a pain to fit.

Baths are popular in our house so do I have to go for the 50 size and shoe- horn it in ?

Thanks Rob

[Nightjar]

Because of loft access restraints, I fitted 2 x 25 gallon tanks, each with its own water inlet feed, and linked the outlets.

[alan_m]

Make sure it goes through the loft hatch - the original may have been fitted before the roof went on.

Size = Fit two smaller tanks

Weight = fit larger tank but only 2/3rd fill it.

You can also get coffin tanks of 100 gallons - long and thin to fit the hatch opening and to spread the load

[Chris Hogg]

As you'd linked the outlets, you'd actually need inlet feed to only one of the tanks. The other would fill through the link.

[Nightjar]

The two inlets ensure that each cistern is filled with fresh water. Without that, you risk there being dead water that never leaves one of them. Subject to the available water flow from the mains, it can also give a faster refill time.

[Fredxxx]

Personally, I would have the cistern on one side and outlet on the other.

Over time, with exacerbated wear, you'll likely find one will cistern will function, and the other will eventually seize up from little use.

[Nightjar]

If you mean the inlet on one side and the outlet on the other, that is usual practice. Again, it encourages water changes.

Because the outlets are linked, water is drawn from both more or less equally. It has worked well for 20 years so far.

[Scott M]

Unless you've got a particularly good bath tap flow and low mains flow & pressure then any old size tank ought to do as, when the inlet is at full chat, it'll fill faster than it'll empty.

[Fredxxx]

That does depend on the cold supply being sufficient. I have known an instance where this was not the case and regularly caused airlocks in the hot water supply.

[Chris French]

Yup, ours fills slower than it empties. There is a pump shifting a fair bit through the shower, or when filling the bath though.

I keep meaning to fit a new ball c*ck which might speeds things up - it leaks slowly and overflows when we are away as well (though I think it will still struggle to keep up). But it's never a problem, I've got about 1000L (200 gal?) up there :-)

[Roger Mills]

What size is your hot cylinder? You need to be able to get all the hot water out of the cylinder - otherwise you have capacity which you can never use. This doesn't *necessarily* mean that the capacity of the header needs to be greater than that of the cylinder because you'll have mains cold coming in at the same time.

It would be worth doing an experiment. Run a bath until the hot tap runs cold, and monitor how low the level gets in the header tank. If it never has less than 10 gallons in it, a 25 gallon tank may be sufficient.

If you *do* need a larger tank, you don't need to completely fill it - as others have said - if weight is a problem. You can mount the ball valve lower down and/or adjust the arm so that it cuts off at about 35 gallons. [You'll need the overflow pipe to be low as well, to prevent the level rising if the ball valve fails to shut off.]

[fred]

In article , robgraham writes

A good sized bath is 20 gallons so I'd suggest that 50 gallons would give a nice reserve.

Life is simpler if you have a single tank as you don't need to consider how to share them properly and there is absolutely no risk of stagnancy.

2 daisy changed 25 gallon tanks with a single fill on the most upstream is pretty foolproof if the slowest to top-up. Twin tanks with a fill in each and paralleled outlets can give more peak flow and can recharge more quickly but there is a definite risk of stagnancy in one of the tanks unless it is carefully tuned. Chose the former unless you have an overriding need to provide lots of water at a high flow rate and fast re-charge.

[harryagain]

This is not an emergency yet but by fortunate chance I've just spotted that the steel water tank I currently have has a very low frequency drip from a corrosion point. Bucket is now in place - not that that will help much if it goes through in a oner mind you !

There are height and possible weight constraints on where I can fit the tank. My problem is that the current tank is 35 gallons and so far all the loft tanks I can find are either 25 or 50 gallons. A 25 gallon tank will go in fairly easily - 50 gallon one will add 150lb to the structure and be significantly more of a pain to fit.

Baths are popular in our house so do I have to go for the 50 size and shoe-horn it in ?

All dpends on you mains water inlet pressure and the size of your baths.

The danger is that as you fill the bath, the loft tank is completely drained. (ie the water is running out faster than it comes in and catches up with it.) As the water level in the tank falls, it comes in faster as the float valve opens more. (Until the ball is left hanging)

So, fill the bath and observe the water level in your existing tank. If there is plenty of water remaining in the tank when the bath s full, you can get away with a smaller tank.

Also, check/adjust the water level in the new tank to maximise (watching the overflow level is not achieved).

[Chris Hogg]

That seems pretty unlikely, but if it's a concern, link the tanks in series: top feed - tank 1 - bottom outlet - bottom feed - tank 2 - bottom outlet to house taps etc.

That would depend on the what was limiting the flow rate, not always necessary anyway, and two tanks in series would fill as fast (or as slowly) as a single larger tank.

[Capitol]

I have 3 x 50 gallon tanks. The guy who built the house originally over engineered a bit. However, when the water disappeared a few weeks ago, we didn't even notice that there was no mains supply for 16hrs. The loft has joists to spread the load of the tanks.

[Capitol]

That would depend on the what was limiting the flow rate, not always

The outlet flow rate would normally exceed the inlet flow rate if you are bath filling with 22mm pipes or larger.

[Brian Gaff]

A lot of people have done variations on this. The big problem is hoe the heck to get the old tank out. Seems it was put in before the roof went on or before the ceiling underneath was finished. Its been in the loft for some years now and its a real pain in the neck, it certainly was for the loft laggers.

I've heard far too many horror stories about cutting it up and setting the roof on fire to chance anyone doing it. Maybe I need a laser cutter...:-) Brian

[Brian Gaff]

Ah, that depends on where the link is hi eight wise and if that c got clogged one might have a problem. However most of the people do use this method, it has to be said. brian

[Nightjar]

...

That still risks having dead water piston up and down in the second cistern.

[Chris French]

We have three 3 tanks, about 1000L in nominal volume I calculated.

Load isn't taken on the ceiling at all (which is good in this old victorian house). There are timber beams running from a chimney breast across to the outside wall of the house and they rest on that