Cold Water Tank in Loft - to keep or not

[Dan Vittori]

Hi All

I have a large water tank in loft which supplies taps and toilets in first floor bathroom and ground floor cloakroom. Rest of all including kitchen, combi boiler and bathroom shower are on mains. I am getting both the bathroom and cloakroom re-done next week. The builder is recommending to isolate/remove the loft tank and use main water supply to all locations. I have no plan for loft conversion in future as height is not sufficient.

I can understand the positives of isolating the tank but not sure if there are any benefits of keeping the gravity fed system for part supply. Can you please advise pros and cons of gravity fed system so as to help me in making my mind up.

Many thanks in advance.

Regards,

 

[ALCPlumbing]

Really the tank should have come out when you had a combi installed. Obviously with a combi your hot water supply is direct from the mains so in order to have equal pressures at your outlets the tank should have been removed and everything should have been connected to the water main.
I recently attended a job where the cold water supply to the bathroom had also been left as tank fed when a combi had been installed. When the shower was in use, due to the flow restriction from the shower head, the mains fed hot water found it easier to push against the gravity fed cold all the way back into the tank in the loft. Unfortunately the overflow pipe from the tank had disconnected and it was overflowing at quite a rate for maybe the fifteen minutes the shower was in use. It caused a fair amount of damage.
This is why you should always have equal pressures at your outlets, especially with mixer taps/valves.
In my opinion only a cowboy would leave the cold supply as gravity fed when converting to a combi boiler system.

 

[JohnD]

When you fill a bucket at the kitchen cold tap, and time it, how many litres per minute do you get?

 

[Dan Vittori]

Thanks both for a prompt response.

The combi was fitted by the previous owner about 3 years back and none of the taps in bathrooms are mixer type so presumably he did minimum effort to save costs. I will be fitting mixer taps now so think will need to use main supply for equal pressure. The builder didn't explain it well. He said it's optional to keep or isolate the tank.

Just done some flow rate tests. For kitchen sink tap only its 14 l/min. With kitchen tap and garden tap (behind same wall) opened simultaneously its 6 l/m for kitchen tap and 14 l/min for garden tap. For garden tap only its about 20 l/min.

Also worth mentioning is that there is only one 1/2"pipe going to loft which is then feeding everything except kitchen area.

Thanks again.

 

[D_Hailsham]

Just done some flow rate tests. For kitchen sink tap only its 14 l/min. With kitchen tap and garden tap (behind same wall) opened simultaneously its 6 l/m for kitchen tap and 14 l/min for garden tap. For garden tap only its about 20 l/min.

The kichen tap is restricting the flow. Is it a mixer type?

The 20 l/min at the garden tap will be the best you can get, i.e just one tap open. When two outlets are in use at the same time the 20 litres will be shared. This should be OK, but don't expect to be able to use more than two outlets at a time without noticing it.

PS an outlet is a hot tap, cold tap, toilet, washing machine etc.

What size is the incoming cold water main? If it's only 15mm, it might be worth increasing it to 22mm.

 

[Dan Vittori]

Hi

Found the stop valve. Its 15mm pipe incoming. The length from water meter to stop valve is about 17 m (13m front garden, 4 meter under floor in dining area. So replacing incoming pipe to 22mm does look like a very costly option.

The loft tank is supplying one bath filler and two basin taps (all non-mixer) and two cisterns. New taps will be mixer type so I think isolating the tank is the right thing to do. Hopefully it should be okay for a family of 4. Please let me know if I need to consider anything else.

Regards,

 

[JohnD]

if you were going to replace it, you would use blue plastic. Most of the effort and cost is digging the trench. The difference in cost between 20mm, 25mm and 32mm is quite small, so get a good big one if you do it. You will probably be surprised what a big improvement you get, if you do it.

Due to the wall thickness, 20mm plastic is about the same i.d. as 15mm copper, and 25mm plastic is like 22mm copper. As plastic comes in long coils, and is flexible, you will probably need no joins or elbows in it, so it is simpler and has better flow.

If your old pipe is lead, it is liable to be squashed and constricting, but you may get a subsidy from your water company Lead Replacement Scheme.

 

[Dan Vittori]

Thanks John. I am getting the loft tank isolated this time. The kitchen project is planned in few months time (fingers crossed). Will keep your advice in mind for changing incoming pipe at that time.

Regards.