Advice for adding propane furnace to wood furnace

[Dennis Mcgee]

Hello all,
My situation is a bit backwards from most. I installed a Caddy wood furnace a few years ago. I am very happy with it, now I want to add a 90% efficient propane furnace in series with my Caddy. I have a blower box ducted to the bottom back of the unit, where the cold air return comes from above. The hot air plenum exits Caddy up of course, through solid sheet metal duct. My question is can I remove the blower box on the back of Caddy and the install a down flow gas furnace that blow hot air through the Caddy into my existing ducts. The new gas furnace would have the return on top. Of course the controls and interlock would need to be changed. Would this be safe and effective? The gas blower would have to pass hot air through the Caddy and the wood furnace would have to draw air through the gas heat exchanger.

 

[flotek]

Just figured I'd ask but Have you considered adding their electric heat element to your caddy as a back up .

 

[Dennis Mcgee]

Yes that would be much easier. I assume that the power bill would be massive. I'm heating about 1,000 sf. of our house. Plus I did all of the work installing rigid duct, insulating etc. Adding a gas unit isn't too bad. I mainly want to have back up for trips, when mother in law is visiting she doesn't have to keep the fire going. Thanks!

 

[stihly dan]

Personally I would do a parallel install. Tie into existing supply and return and add backdraft dampers.

 

[Need2Saw]

This is my system, parallel with back draft dampers, works great.

 

[laynes69]

You can choose parallel, but series is very simple. There should be access panels on the sides at the bottom that can be removed and ducted from the central furnace. The only problem if you choose not to burn wood, the new furnace will have to heat the mass of the woodfurnace before producing heat in the home. The benefit of this setup is the lack of dampers that would be required, unlike parallel where backdraft dampers are a must.

 

[stihly dan]

This is my system, parallel with back draftView attachment 466308 dampers, works great.
View attachment 466308

That's a good looking install.

 

[Dennis Mcgee]

Yes that is a clean install. I appreciate the input. I am thinking that I will start planning a horizontal parallel system with dampers. I like the idea of two independent blowers.