Backdraft damper for wood furnace install

[andym]

I'm in the process of installing a Drolet Heatmax2 wood furnace. It's a parallel installation sharing the supply and return with my LP furnace. I plan to only use the LP as backup (thermostat set to 62 or something). I've pretty much got the ductwork planned out and in the process of installing. I need to order a couple of backdraft dampers:

For (above) the wood furnace I need a normally open, power close damper.

For (above) the LP furnace I need a normally closed, power open damper.
Correct?
(Both dampers will be located in horizontal runs of duct. )
(More questions once I make sure I'm on the right track here?)

 

[brenndatomu]

Have any pics of the overall setup? I do better hands on, but pics will help a lot too.
Any way that one or both can be substituted with a gravity damper?

 

[Bad LP]

Why would you not have all NC dampers that open with power on?

I have no idea about safety in a power failure.

 

[andym]

Any way that one or both can be substituted with a gravity damper?

No time to post pics now. I was checking on retrozone.com and I wasn't clear if gravity was even available. Gravity would work for the LP side if it can be installed in a horizontal run.