Vented cylinder in the loft

[Benjibalz]

Any thoughts and advice would be appreciated. My customer has a 26kw combi and low water pressure and flow. The development of the property would mean 2 bathrooms in addition to the kitchen plumbing.

They want hot and cold supplies to the 2 showers that cannot be affected by drawing off water from other outlets but do not want a cylinder in the airing cupboard as this will provide additional space to a bedroom.

An unvented cyinder with the combi will not gaurantee the necessary flow rates for the showers so an alternative solution is needed.

I'm thinking about installing a 50 gallon cistern in the attic with a vented direct cylinder situated a couple of feet below. Basically, the base of the cistern will be level with the shower outlet of the cylinder(approx 1/3rd down). I'm looking at installing a 3 bar negative head pump at the base of the cylinder to provide hot and cold water to the 2 showers only.

My concern is the level of the water in the cwsc dropping below the top of the cylinder and in turn drawing in air via the vent. Any thoughts would be gratefully received. Cheers, ben. Ps: they have s**t loads of money but no budget!

 

[ChrisR]

It does sound llike you're asking for trouble. So often they end up sucking air down the vent.
I prefer to pump the outlet from the citern into an UNvented cylinder.
There's almost no way you can guarantee that ther will be NO interaction whatsoever between drawoffs.
Careful with the HW capacity. A standard 36x18 lasts a few minutes with 2 strong showers

 

[heatingman]

stick an-unvented cylinder in loft and use a mains booster, in loft next to it. Just use the combi for kitchen or utillity.
Contact Friendly-Water 01932 245200 for info on the boost-a-main system.

 

[Benjibalz]

Appreciate the replies but I know I'm asking for trouble! As mentioned the customer is a bit shy on the funds and running a 22mm cold mains into the loft is a no go.

Therefore my question of the height of the cwsc in relation to the cylinder still stands although I think ChrisR has probably answered it unless otherwise? Air intake is the issue.

Once again here is the key point.........

If I install a cold water storage cistern with the base, level with the secondary outlet on the hot water cylinder incorparating a negative head pump will it work??!

 

[Benjibalz]

Remember heatingman I mentioned the customer was tight on funds despite being able to buy my house 3x over!

So unvented and a mains booster are a little too pricey, ie: megaflow & accumulator.

 

[mehran]

I have just completed a job were I installed a 210L twin coil vented cylinder and pumped the outlet with an 3.6bar negative head salamander. it is feed with a 50gallon tank. 22L/m flow at the bath which mean 2.5bar dynamic pressure left in the bank

but in my install the loft tank was about 3m above the top of the tank.

it will work but. as others have said:

A, must must stop it from sucking air
B, it will drain a hot water tank is no time so you need to size it with that in mind
C, the pump will make some noise
D, Why take the hot water off at 1/3 down the tank? why not use a Surry flange?
E, why cant you put the CWT fully above the hot tank?

 

[Benjibalz]

Cheers Mehran, good to know you've done something similar successfully!

I've just got back from the site and we've decided to install a Gledhill horizontal cylinder and also up the size of it. This will mean the cylinder is situated below the cwsc.

We've never installed a horizontal cylinder so if anyone has any points regarding the installation or anything we should be aware of I'd be grateful of yours comments. I presume its just like installing a vertical one but its on its side?