Combining wood heat with a propane boiler

David_29

My customer has a Buderus boiler installed in 1998, by another company. He has 2 zones, one circulator with 2 zone valves. The system works fine, though it did take some extra bleeding. It is baseboard installed on a two-pipe system. I think an earlier incarnation had cast iron radiators.

In the living room is a wood stove with a water jacket built in above the firebox. With no wood burning, the stove heats nicely from the hot water from the boiler, and the stove acts as a heat source for the living room.

Right where the 3/4" copper tubing is fitted to the wood stove is a standard boiler pressure relief valve and a thermostat on the tubing. Before the Buderus propane boiler was installed, the old oil boiler's controls allowed the stove to heat the water for the hydronic system, either on its own or in tandem with the boiler. Now, if you light a fire in the stove, almost immediately the pressure relief valve will open, since the stove thermostat no longer actuates a circulator. So, not only will the wood stove no longer help in heating the water in the hydronic system, the wood stove can not have a fire at all.

The customer has lived with it for 7 years, but he thinks the clever and resourceful people of Aquarius Plumbing can restore the system's old usefulness and efficiency.

The control challenge is to have the thermostat by the wood stove open the appropriate zone valve and start the circulator, without firing the boiler, yet letting either of the room thermostats open the zone valve, start the circulator, and fire the boiler.

Or will it take a parellel zone valve and circulator, so the wiring between wood and propane is entirely separate.

HELP!

hr

That can be a risky animal

to mess with. Actually with no fire in the stove, and the boiler heating the stove, you actually have a cooling tower! Some of the energy from the boiler is going up that stoves flue. As the flue has a draft and hot air rises, this could be significant

The problem with the wood stove HX is controlling the things from overheating and flashing to steam. You need to be sure you always have flow and a place for those BTU to go. When all zones satisfied where will the output from that stove HX go? Good chance it will overheat the system, possibly pop a relief and maybe a mess or dry fire condition in the boiler.

Improperly flowed they can rob too much heat from the flue gases and actually cause condensing and creasote issues in the wood stove flue. Be careful. You don't see many of those things sold anymore. Quite a liability potential, I suspect.

hot rod

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