Upgrading my existing loft cold water tank

[MarkHan]

Hi,

I'm about to install a thermostatic power shower in my upstairs bathroom, but my gravity fed system cold water tank in the loft isn't big enough (it consists of two 13.5 gallon tanks joined together by a short pipe at base level), to supply the flowrate that will be generated by a decent power shower (or, so I've been told by the manufacturers of the shower). They say I need a minimum 50 gallon water tank(the shower can supply around 18LTRS/minute at 0.1 bar pressure, so presumably a lot less than this at a working pressure).

Is this true or can I get away with with the 27 gallons we have at the moment(the hot water cylinder is big enough). The shower will be used a maximum of around 10 minutes at a time.

If I do need to upgrade my water tank, does anyone know if I can just "extend" my tank by adding another tank "module" connected by a further pipe at base level, to avoid messing around with the inlet and outlet pipework connected to the first tank?

Sorry to be so long winded.

Thanks in advance.

 

[AdamW]

Well, the water coming from the hot cylinder is replaced with water from the cold loft tank as it is used (i.e. gravity fed). So, despite your hot cylinder being big enough the real issue is your cold tank.

Your tanks are 27 gallons in total, which is about 120 litres. Your pump is assumed to be pumping 18 litres per minute for 10 minutes, which is 180 litres. Despite the fact that the tank will be replenished the whole time by the mains, I think you run a risk of emptying your tank here.

I am not a plumber, but I would think that it would be fine to add another tank (or two!) onto the current set-up in the method you propose.

 

[AdamW]

Something just occurred to me: would I be correct in assuming you have a bath? If so, does the cold water come straight from the mains or the tank? If it is from the tank then that sounds strange as I thought baths were all 200 litres or more.

If your current set-up can totally fill a bath in a reasonable time (only if the cold is from the tank) then it could be fine.

 

[MarkHan]

Thanks for the reply AdamW,

My bath cold supply is from the loft tank, and I will try and run the bath to see how quick it fills etc. I'm pretty sure it's OK for a full bath but I might just "extend" the loft tank to be on the safe side anyway.

Many thanks for your comments.