Moving cylinder into loft under water tank

[Rangie427]

Hi,
I currently have installed a gravity water system (hot + cold taps) with a fully pumped, Y plan open vented heating system, in a normal 3bed semi. Im now looking to have my hot water cylinder, heating pump and controls moved into the loft under the water tanks.
The water tanks are situated on a stand in the apex of the roof and the base of the water tank is 5foot from the roof joists. There is enough space underneath to resite the indirect 42x18 cylinder with heating pump and controls.

My main area of concern is the design of the heating system with the open vent.
Can i still use the fully pumped heating system with open vent? as the vent pipe would be tee'd into the system in the loft rather than lower down on the first floor. Again im concerned about the pump dragging air into the heating system.

I also realize that i could do away with the expansion tank and go "sealed heating system"
Does this just mean adding an expansion vessel, pressure relief valve and filling loop in place of the expansion tank?
If so, how do i size the expansion vessel for my system?
Does anyone have a pipework diagram of a sealed system?

Thanks in advance

 

[kevplumb]

owzat

 

[Rangie427]

Thanks kevplumb

Any idea what size expansion vessel i should use?
extended 3 bed semi with 11 radiators.

 

[kevplumb]

depends on the system volume

 

[Rangie427]

I can't find the volume control

Sorry could'nt resist, How the hell do i find out the system volume?

eg; Boiler + 11 Radiators + Piping = This one should do!

 

[nickso]

most houses get away with a 10 litre expansion tank.....if you think you have a bigger house put a 12 litre in.

 

[Softus]

My main area of concern is the design of the heating system with the open vent.
Can i still use the fully pumped heating system with open vent?

Yes.

...as the vent pipe would be tee'd into the system in the loft rather than lower down on the first floor. Again im concerned about the pump dragging air into the heating system.

If you pipe it correctly then it can't happen - as has been written many times, in many places, including on this forum, the sequence of connections should be (in the direction of flow): vent, then the cold feed, then the circulating pump, then the MZV(s).