Adding a back boiler

SDH

Can anyone advise on the pros/cons of the adding a back boiler into an existing heating system?
The existing system is a pressurised gas fired system.
I have been given two options;
1) put a heat exchanger on the existing system and leave it as a pressurised system & connect back boiler to heat exchanger
or
2) convert existing system to an open/vented system and connect the back boiler into it

Any thoughts on pros/cons/future problems?

Thanks

Buford T Justice

Back boilers on pressurized systems is not recommended at all.

SDH

Thanks Fingers.
Are there any problems with converting the pressurised system to an open one?

Plombier

put a heat exchanger on the existing system and leave it as a pressurised system & connect back boiler to heat exchanger

This is a better way to do it and is perfecty safe.

Most gas boilers wont work if there not pressurised.

Buford T Justice

Depends on a few factors.

1) I'm not aware of any systems on gas as open, but someone else can advise here, like Sparkpea or nptm

2) Is your attic a conversion, or is it just an unused space? If you decide to put in the F&E Tank in the attic, and there is a rad at the same level or higher, it won't fill as its above the level of the tank.

3) Is you're hot water system pressurized or open? If its open, then there would be a tank in the attic, which means there is mains there already to use the F&E Tank.

Pressurized is generally a better system though, better circulation

SDH

Thanks guys.
@ Fingers - Attic is not converted, and there is a tank there so no rads above tank.
(I assume you are asking about the domestic hot water?) I think that system is open and is fed from the tank in the attic.

@ Plombier - is there a way to check if the gas boiler will run on an open system, before we actually change it!? (We got a ridiculous quote from a crowd on the east coast to supply & fit a BB stove of >10k using the heat exchanger method, but a much more reasonable quote to "open" the existing system and connect the BB into it, hence we want to go that route!)

Plombier

Measure the heigth above the gas boiler in meters to the heigth of the new expansion tank in the attic and multiply by 0.09804 reduce the pressure in your heating system to below this if it still works its ok.

Buford T Justice

Plombier wrote: »

Measure the heigth above the gas boiler in meters to the heigth of the new expansion tank in the attic and multiply by 0.09804 reduce the pressure in your heating system to below this if it still works its ok.

Is that figure used to calculate the pressure achieved in bar by gravity?

Plombier

Yes

SDH

Great - thanks guys.

SDH

SDH wrote: »

;
2) convert existing system to an open/vented system and connect the back boiler into it

You can't fit a back boiler in such away that it can impact on a gas boilers performance, a gas boiler must be able to control water temperture and if it's trying to disipate heat you can get problems if you have a high return temp due to a secondry heat source.