correct size expansion vessel?

[fingertight]

Hi chaps,

im lookin at updating a system, the plan is to remove old boiler and cylinder out of loft, then install worcs 24 ri (conventional) and high recovery cylinder and pressurising the system.

Its a bungalow with 18 rads yes 18 rads!!! i have used an on line calculator to find what size vessel ill need (dont know system volume) and its saying that a 20ltr vessel is req'd. Could anyone give me a bit of reassurance to confirm this? my work mate is sayin thats too large?

thanks in advance

 

[nickso]

you cant really go to large, only too small and therefore not provide enough expansion.

20 litres is big and more expensive but if you have the space and believe your calculations to be correct just do it. i see some bigger houses struggle on the usual 8-10 litre vessels.

 

[baxpoti]

my work mate is sayin thats too large?

Your work mate is wrong!

 

[Gasguru]

Stick a 35 litre vessel up in the roof, cover it in fibreglass insulation to stop it freezing. Sometimes the vessel will even sit on top of the cylinder. The system will go for years without needing a top up and the pressure will barely rise on heating leading to far less stress on the system. This size of vessel normally has nice little feet so no wall brackets etc. About £30.00 and double dose the inhibitor would be a good idea.

 

[fingertight]

thanks guys, i appretiate the knowledge thats on tap here!

 

[muggles]

Stick a 35 litre vessel up in the roof, cover it in fibreglass insulation to stop it freezing. Sometimes the vessel will even sit on top of the cylinder. The system will go for years without needing a top up and the pressure will barely rise on heating leading to far less stress on the system. This size of vessel normally has nice little feet so no wall brackets etc. About £30.00 and double dose the inhibitor would be a good idea.

Just make sure it's on a good solid base, as a 35L vessel's going to weigh close on 50kg when full, and that's 12.5kg's per 'nice little foot'. Lots of pressure on a very small surface area...

The water in your system will expand by (roughly) four percent from cold to hot.

 

[WDIK]

as a rough guide its about a Ltr /Kw but on dommestic system you can you can get closer.

what you need to be looking at is complete thermal coupling.
that means its doing its job ie the bag pressure is set and it couples