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Got a Combi Boiler want to add a log burner to run radiators

Postby Kersh » Thu Dec 11, 2008 6:36 pm

Hello I'm a newbie so here goes...

I've already got a combi boiler and am about to install a log burner which has a back boiler in the house, I would like the log burner to run the central heating in conjunction with the combi.
I have heard that a heat exchanger will be needed to do this - can anyone recommend what sort of heat exchanger I will need and any tips!
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Postby plumbbob » Fri Dec 12, 2008 5:37 pm

There is a whole bucket full of problems that would need to be overcome before being able to connect a log burner to a pressurised heating system and to be honest, I am not sure it can be done. This topic has been raised on this forum quite a few times before, and I have never seen anybody offer a complete solution.

Combi's are generally not suitable for connection into a system where a secondary heat source is utilised. This is often stipulated in the installation instructions. The pump needed to circulate the hot water is an integral part of the combi so not sure how it could control water from a log burner. The safety aspect has to be considered too, particularly that the water has to circulate constantly, to avoid it boiling, and what happens if it does?

I don't see how the inclusion of a heat exchanger fits in to the equation at all. We often see installations where log burners are installed in circuits with system boilers, but not combi's. Different animal altogether.
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Postby simon@hwch » Sun Dec 14, 2008 1:28 pm

You will need to add a heatbank to link a sealed system (the combi) with an open vented system (log burner).

Log Burners are an unrestricted heat source, so can be dangerous with sealed systems because if the water reaches boiling point you will have an explosion.

Some up market european stoves can be fitted with a quenching valve and connected to unvented cylinders, but this system is not approved for use in the UK.

So you are back to a heatstore.

Please also bear in mind that a normally clean burning log stove has the temperature inside dropped by a water heat exchanger, and this causes incomplete combustion resulting in the generation of tar deposits in the stove.

Some of the more honest and experienced manufacturers will warn you (eg: Clearview) others will not mention the pitfalls in their literature.

I have a logburner and use it in my lounge to good effect - but there is no way I'd connect it to the CH or the HW. They work longest and best as a space heater.
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