cold water system unusual

[need2 knowmore]

A friend has recently moved houses. The house he has gone into has an unusual cold water system. It is a fully vented system with 2 unlinked cold water head tanks, one tank is 50 gall. with a single outlet that feeds the whole cold water system and the hot water cylinder. The other tank is 25 gall. it feeds a single shower via a shower pump. The hot water for the shower pump is fed from the cylinder via an S flange.
It all seems to work OK, but is it a disaster waiting to happen ?
I thought good practice, was to have a single large cold water head tank with 3 take off's for the shower pump, the hot water cylinder and the rest of the house cold water supply.
It is a Victorian house over 4 floors. the cold water tanks in the loft are on a raised platform approx 2ft above the floor, the single shower is on the top floor with the pump in the loft. The hot water cylinder is on the 3rd. On the ground floor there is a single gravity fed shower ( good flow because of large static head.

What do you think of this arrangement ? :nonod:

 

[hammers4spanner]

does it work?

 

[need2 knowmore]

It seems to work OK. but my friends family is larger than the previous owners and I am wondering if this might be a problem since the system seems to be in conflict with what is advised good practice, or are these advisers just playing safe. ?

 

[Kevan]

The only sensible thing I can think of for this extra 25g tank is to allow more than 1 shower to be used at the same time without loosing the pressure. If the ground floor shower were in use at the same time as upstairs shower both drawing water from a single outlet from 1 tank the water would be used very fast, however with the setup you describe the upstairs shower will get its head from the small tank, leaving the rest of the system to work properly. How is the water heated?

 

[need2 knowmore]

The water is heated by a Gas Boiler and an indirect vented cylinder(106L capacity and I think that is too small and suggested replacing it with a 206L cyl.).
I think it probably works because the 25gall (113 L) tank only supplies the cold water to one shower. If the shower uses say 15L/min. Then 10L/min would be hot water supplied via the 50gall head tank and the h/w cylinder and 5L/min would be coming out of the small head tank which even if there was no c/w going in would allow a 20 min shower, but with normal make up rate of c/w the small tank is unlikely to empty and allow the shower pump to run dry. What do you think.
Even more concerning is the fact that the larger head tank has only one c/w outlet which has to supply all the house c/w requirements plus feed the h/w cylinder for the rest of the h/w requirements. What do you think of that arrangement.

 

[jhon lennon]

the kitchen tap should be fed direct from the street but otherwise that arrangement seems fine

 

[Nostrum]

Can you not just link them up and be done?

I take it your worried that the cold water tank feeding the shower will run 'dry' leaving a scalding risk?

I take it the tanks are on the same level?

 

[need2 knowmore]

Yes, both tanks are on the same level. What size pipe for the link ?
Two things still concern me.
The shower pump is a stuart turner, I phoned S/T and told them the set up, they said the pump must be fed from the same tank that feeds the h/w cyl. and not a separate tank, is this to ensure that both the h/w and c/w entering the pump are at the same static head or are they just covering themselves ?
Also the single feed from the larger c/w head tank feeding both the h/w cyl. and the rest of the c/w system, what is the danger there ?
I am uncertain about the whole arrangement, but my friend cannot afford to spend a lot of money changing it plus the disruption to the family life whilst it changed.
Do you think it is OK to leave it and see how it goes ?

 

[Nostrum]

I would link them together with a piece of 28mm and 2 x 28mm tank connectors, job done in an hour or so. Just check the water levels in each when you link them up, if one is higher than the other you could be in some bother when they level out!. If you left in the 2 ball valves in you won't have any problems with the tanks running low!!

Can't see any other issues with it. It would probably work forever more as it is but say the small tanks ball valve got stuck....

 

[piyingoa]

however with the setup you describe the upstairs shower will get its head from the small tank, leaving the rest of the system to work properly.

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[PlumbBobBob]

the reason stuart turner state that shower hot and cold should be fed from the same cold tank is that if the cold runs out because the tank is smaller there is the chance of getting scalded.

 

[need2 knowmore]

What about the larger head tank having only one outlet that feeds the h/w cyl. plus the c/w sytem apart from the kitchen tap.

 

[Nostrum]

If you join them up you'll effectively have 1 large tank so it won't matter.