Wood Furnace and downflow heating system?

Welcome to Hearth jack! Well, if you were gonna do this, know that you would have to have the blower running at all times (when burning) since you would get no gravity heating. you would also have to install a emergency heat dump for power loss etc. like this one http://store.yukon-eagle.com/safety-heat-dump/
Also, no mfgr. that I know of would endorse this, which means your HO ins won't either

actionjack said:

My thought was having two thermostats (IE: have the wood burner set at 75 and furnace set at 65 in case I work late and can't make it home to keep fire going

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Yup, that's pretty common. My Yukon wood/oil combo furnace uses 2 stats from the factory, it has a circuit board that locks out the wood damper if the oil burner kicks on (but that never happens at my house )

The limit switch will kick the blower off when temps cool.
You have friends that have these units and you still want one?! I bet one of your buddys would sell ya one cheap.
If you are looking for a budget wood furnace, Englander (http://www.homedepot.com/p/Englander-3-000-sq-ft-Wood-Burning-Add-On-Furnace-28-3500/100185844) makes one that gets good reviews, US stove, not so much, Daka, meh...

Oh, OK, well FYI about the only box store add on wood furnaces worth looking at would be Drolet Heatmax or the Englander, in that order IMO. If you can pony a bit more cash up look at the Caddy line https://www.google.com/url?sa=t&rct...yOT-yZOFcEX91Brda5eMVYg&bvm=bv.77880786,d.b2U similar to the Heatmax only heavier duty materials.

Oh, just re-read your OP. Better check with your local codes, in a lot of places a wood burner in the garage is illegal. Also, tying into existing duct work will reveal some safety clearance issues with the ducts I'd bet (for wood heat, not as is now)

Also, if crawl space is unheated you will need to insulate the heck out of the ducts to keep from losing all the heat to it

Just giving ya a heads up...

I live in a tri-level and have this very setup.
Yes to the heat dump.
Blower does not need to run continuously. It will most likely run much of the time anyway except at the beginning and end of burn cycles.
I have about 10' of regular ducting out of plenum to wall of furnace room . then flex duct through wall into crawl space where it goes through a 15" , 14 foot long culvert pipe to tie into main house duct work.
The culvert after going through wall actually travels outside for 3' before going into crawl space. Snow will build up on the pipe so I know there is very little heat loss. This surprised me many years ago when I set it up this way. Thought I would have to spray foam the pipe to keep from losing heat, but not the case.
Agreed on spending the extra $ for a better furnace.

actionjack said:

OK good to know JustWood. But to brenndatomu's point I talked to my insurance agent and having it in the garage is against code, has to be inside or outside house. Guess I'm going to have to rethink my options now. I could easily put an outside add on furnace (would actually be easier), but man they are much more expensive.

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Use more wood too...might be worth a shot though, insulate the heck out it! Or build a well insulated doghouse around a regular wood furnace ducted into the house...?

I think there have been some on here, if not there is on that other woodburners site "AS", or check youtube...
Edit, better double check ins co again, some don't want a wood burner even outside! (time to shop for new ins if that is the case!)