I dont have much to add to your idea other than running the flue as you mentioned but that seems very wasteful and inefficient like you said. You could do a rocket mass heater but Im not sure you could fit it in there either. Search youtube and youll see a bunch of them

Im having to move this winter and need to build a quick greenhouse. Did you have plans for this or is it "free hand". Looks like a lot of fittings but very well done!

Ill probably end up doing a hoop house but this looks like a good plan also.

Thanks

Mike

Putting the wood burning heater outside would be best. The heater may get too hot and melt the or weeken the structure.
Another thing to consider is the amount of O2 the heater will burn, so if it does not have a fresh air port it is likley not to work properly for you.

You might build a structure made of cinder blocks next to the greenhouse, use some flashing and build a duct from the top of the heater to the greenhouse. If you have a power source you could have a duct fan to move the air fron the heater to the greenhouse on really cold days.

Mike #2

A stove that was small enough to not melt your structure would also be so small that you would have to keep re-filling it with wood every couple hours all night long.

I built a 12x12 shed to house the wood furnace for my 14x48 greenhouse. The stove is a forced air wood furnace. Water is more efficient to heat and circulate, but I was given the stove. I connected it to the greenhouse with a two 6" insulated ducts to move air back and forth. You can see the shed in the back of this pic:
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Heating poly is a pain because the r-value is so low. My inflated double layer has an r value of 1.4, which stinks. That makes wood heat very attractive cost-wise, but I was loading the furnace with wood at least three times a night every night from 8pm to about 2am. It is a lot of work.

New pics! I decided to build a concrete room that will house the wood stove. I expanded the greenhouse to 18'x8' and it is 10' high at the peak. I installed framing that consists of a 4"x6" main beam and two 4"x4" posts cemented into the ground.

The metal roof and framing are done. Woodstove installed and 3 yards of pea gravel is spread. Next up is the siding, plastic sheeting and door installation!

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Nice work. It looks sturdy.

The stove will be more efficient if you connect a hose to the air input that brings in fresh air from the outside. Otherwise, your fire will combust with the air from inside the structure, then expel that air, and the vacuum will bring in cold air from the outside into the greenhouse, working against your heating efforts. Cold air burns hotter, anyway. My wood stove has a blower on the front, and I can't get it to burn hot without either the blower on or the door open.

Do you plan for the sides to roll up? Opening the door at one end won't be enough ventilation.

Remember to cover all of the sharp edges before you put the plastic on. I use white duct tape. Those metal conduit straps are murder on poly, but they're fine if you put enough tape over them.

if I may ask, why not use polycarb? You have gone through such expense already why not make it better at holding the heat in.

mike

Greenhoue is done. I didn't use polycarb because plastic forms to the structure easier. If I have to replace it each year, it's only about $40 per replacement, so low cost overall.

Pics!!

The front.
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Right side -- wood stove pipe in back.
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The left side.
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Opening the door and looking inside.
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Lighting. I run this for several hours after sundown and should help keep plants moving.
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Plant benches - need plants!
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Windmill palm seedlings on a bench.
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More windmill palm seedlings. Barrels have water in them.
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Some plants.
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Wood stove and fan.
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Hoping to fill it all up soon!

Good job with the heating. A friend built a rocket stove and bench for his greenhouse, but said it had to be fed too often to end up being practical.....

My concern is that you have gone to so much trouble to build, heat, and furnish your GH, but not much effort and expense to cover it. Some folks put a blanket of bubble pool cover over their whole GH for the winter with excellent results - right over the plastic. You might do some research on that and see if you can take your cover to the next level.

Is this double wall poly or single? You really need 2 sheets with 4 inch of air space between. You should have insulated your north wall in your zone. This would cut your heating in half at least or more.

There's that cold air intake for the stove I wanted to see. That actually makes it safer to use, too, but it is still worth the $12 to put up a carbon monoxide alarm any time you are combusting anything indoors.

Maybe you are a lot neater than me, you are certainly a much neater carpenter :) but I would end up getting those plywood benches wet too much and messing up the plywood pretty quickly. Painting all the wood white would also help it to be brighter inside.

My biggest concern would be ventilation. It looks like your sides don't roll up, and you can only open one end. You need some way to expel the air when it gets too hot. At this point, it would be worth it to hook up an exhaust blower at the stove end as an emergency measure to keep it from getting too hot. You might also put in whatever little windows/vents that you can fit into that end. A cross-breeze is good for the plants in a lot of ways beyond temp control, too.

Good job, and good luck with everything.

Thanks for the advice guys. I was going to worry about ventilation in a bit as my pocketbook is still recovering, lol. With the sun angle so low this time of the year, I'm only getting 30-35F over outside temperatures with full sun. So if it's 50F out, it's warming to 85F during the day. I have a remote sensor in there that transmits the temp every 5 minutes to a website where I can monitor it very easily.

As for insulation, my wood stove can heat it 50F above outside temperature -- at least that's what it has been able to do so far. So if it's 0F outside, I'll have a 50F internal temp. Add in sun and I'll be at 85F. (I plan on throttling the stove back on sunny days so it doesn't get ridiculous in there).

Now for ventilation, I could go with a fan/intake damper setup, but I'm wondering if I could use those automatic vent openers that I see on eBay, etc? I could put two low on one wall and two high on the other wall to create some sort of natural ventilation. Put the low ones on the wall toward the direction of prevailing winds, etc.

http://www.ebay.com/itm/GREENHOUSE-SOLAR-POWERED-AUTOMATIC-WINDOW-VENT-OPENER-/390477604457?pt=LH_DefaultDomain_0amp;hash=item5aea476669

Could I somehow hook that up to a plywood square to open/close and wall mount it?