Drolet Heat Commander Backup Install

[NorthernNY]

Hello everyone, I have been reading several of the posts on here about installing a wood furnace in addition to a gas furnace and come to the conclusion that each install is individually slightly different. I recently bought a 1000 sq ft house that has a newer condensing propane furnace and I want to add a wood furnace to the house to reduce the amount of propane i'm using. Im considering the heat commander from drolet. From reading the fourms i have gathered there are two ways to accomplish this. The heat commander is on its own entire system or it is piped into the ductwork the propane furnace is with some safety measures to make sure they don't run at the same time. I have attached a layout of the current system with the blue and red being the current cold and hot ducts. If I could pipe the heat commander into the existing duct work that would be preferential and is exactly the setup when I purchased the place but without any safety measures to ensure back feeding or both running. Im attempting to correct that system. If that isnt a possibility I added in green where I could run heat commander ductwork in the house. Any of the lines on the diagram to go to a rectangle go upstairs and any without provide heat to the basement. I should add the old system had two 8 inch lines piped into the 8x14 trunk line and fed the house like that, which I know is a problem and won't work well for the heat commander. Thank you for the input in advance.

 

[laynes69]

The heat commander has an interlock built into the motherboard. When wired (2 wires) if the central furnace would run, the heat commander blower will stop until the gas furnace stops then continue. A 1000 sq ft house, your central furnace will never run as long as your using the woodfurnace.

As long as you meet the requirements for the necessary ducts (supply and return), you'll be fine. I installed a simple damper that opens when the LP furnace fires, and installed a manual damper for the woodfurnace. In my case, I didn't wire my interlock because my LP furnace is off.

 

[NorthernNY]

The heat commander has an interlock built into the motherboard. When wired (2 wires) if the central furnace would run, the heat commander blower will stop until the gas furnace stops then continue. A 1000 sq ft house, your central furnace will never run as long as your using the woodfurnace.

As long as you meet the requirements for the necessary ducts (supply and return), you'll be fine. I installed a simple damper that opens when the LP furnace fires, and installed a manual damper for the woodfurnace. In my case, I didn't wire my interlock because my LP furnace is off.

Thanks for the reply. I have read previously that the heat commander has a built in interlock which is great. I'm looking for a little more input on the ducting. My understanding is that I would need a damper on the 8x14 trunk line to prevent the HC from pushing into the LP furnace. In addition since the HC has 6inch outlets would an acceptable method be to pipe in several of the 6" lines into the 8x14 trunk line?

 

[brenndatomu]

Thanks for the reply. I have read previously that the heat commander has a built in interlock which is great. I'm looking for a little more input on the ducting. My understanding is that I would need a damper on the 8x14 trunk line to prevent the HC from pushing into the LP furnace. In addition since the HC has 6inch outlets would an acceptable method be to pipe in several of the 6" lines into the 8x14 trunk line?

Yes, you will need a simple gravity damper (flap) in the 8x14...and you could put up to 4 of the six 6" ducts from the HC in the 8x14...any more than that the 8x14 will cause a restriction if the HC blower needs to run on high in an overheat situation.
Or if you are going to run the HC exclusively (normally) you could also just drop a piece of cardboard, or sheet metal in next to the gas furnaces air filter to block off backflow...just need to make a red flag or some kind of a reminder for the gas furnace power switch that is hard to miss, so you don't try to run the gas/AC with the blower blocked.
Oh, and the HC is a lot for 1000 sq ft...unless its as tight as a barn.

 

[NorthernNY]

Yes, you will need a simple gravity damper (flap) in the 8x14...and you could put up to 4 of the six 6" ducts from the HC in the 8x14...any more than that the 8x14 will cause a restriction if the HC blower needs to run on high in an overheat situation.
Or if you are going to run the HC exclusively (normally) you could also just drop a piece of cardboard, or sheet metal in next to the gas furnaces air filter to block off backflow...just need to make a red flag or some kind of a reminder for the gas furnace power switch that is hard to miss, so you don't try to run the gas/AC with the blower blocked.
Oh, and the HC is a lot for 1000 sq ft...unless its as tight as a barn.

Yes the HC will be the main source of heat 95% of the time except when im not home. I would prefer to have the damper built into the trunk line so I don't have to remember to remove the air filter block. I would also need to have dampers on the 6" lines from the HC as well if the LP were to run correct? The house was built and insulated in the 1960s, so by todays standards not well insulated but not terrible either. I would also run a couple lines off the HC in the basement so it would be heating more than the 1000sq ft living area. Where would you recommend getting the damper i am having difficulty finding an 8x14 gravity.

 

[brenndatomu]

I would also need to have dampers on the 6" lines from the HC as well if the LP were to run correct?

Well, yeah...kinda sorta...you need something, but I hate those little spring dampers because they block gravity flow of the heat of the power goes out...things can get pretty hot if it happens right when there is a rippin fire.
I prefer (and have) a power closed/spring open damper on my return air duct to my Kuuma...it closes when the oil furnace/AC runs, then always open otherwise.

Where would you recommend getting the damper i am having difficulty finding an 8x14 gravity.

Yeah I dunno if I've ever seen one for sale...more of a custom part...either make it or hire the local HVAC or sheetmetal shop make you one to fit