I hope you're not too fond of sleeping through the night. I have a large wood furnace in an exterior building. It has a blower feeding air to the fire. Even packing the thing full of wood, I only get about 3-4 hours of decent heat, which means that I am out there at 2 or 3 in the morning feeding the fire. You might have better luck with a small internal stove, but it's still a lot of work to feed the fire. It makes me understand why the Amish have so many children :)

I have a coal stove in my 12x24 check it out under my member name ...we love it some nights I get 7 hour burns

From what I have seen in GH's, wood stoves work if you have a fairly large GH with sufficient volume and thermal mass, and if you are just using the wood heat on particularly cold nights to "take a chill off."

If you are thinking of using the wood heat as a frequent source of heat, or if your space is small, then it would likely be hard to do. You would need to be in the GH quite often to manage the fire (keep it going, and not too hot). For a GH the size you mention, it may be hard to find a wood stove small enough to not overheat the space.

try a rocket stove

I use a wood stove in my 20 by 30 greenhouse. It can give me a 20-25 degree heat gain from the outside temp. Firewood is cheap for me (free if I feel like hauling and chopping and loading. I have used other types of heaters and all of them have their plusses and minuses but I haven't found anything that puts off as much heat as a well managed wood fire. Dealing with the wood and ashes gets messy and there will always be smoke leaks as you start the fire so you have to put up with smoke sometimes. Some wood burns hot and fast and some wood burns slow and low - this is hard to regulate. Some times fires can be hard to start and you will be starting a new fire every time to walk out to the greenhouse. But again - NOTHING puts off as much heat for the size of a wood stove.

I use a kerosene heater as back up for really cold nights and it also does a good job of heating up the space. Maybe a 10 - 15 degree heat gain. On a really cold night (in the teens outside) I can run both heaters and keep the greenhouse above 50 degrees.

The main problem with heating a greenhouse is that it really needs moving air to get the warmed air into every corner. If the power goes out, your fans won't work and the corners are going to get pretty cold.

My greenhouse is larger than most of my friends and none of them use wood for heat - most use propane. My heating costs are often less than half of what they pay to stay warm. You'll be surprised what it costs each month to keep those plants happy. That's why you'll see a lot of unheated and unused greenhouses in backyards.

I received a free wood stove from someone and incorporated it into my 22X28 greenhouse, with ceiling about 10' high. It is still a work in progress, I don't have fans set up to distribute the warm air and need to do a much better job of sealing the air leaks. On top of that, the stove itself is a rather cheaply made old sheet metal unit that does not radiate heat very well at all, I can stand directly next to it and feel very little warmth, most of the heat is radiated from the black chimney pipe. All that being said, it does a good job of keeping the central area of the greenhouse around 45 degrees when temps outside are in the 20's. I often get it going at night when temps start to dip below 40 and stoke and feed it again just before turning in around 2:00 a.m. I make a point of staying up til' then on a night when I'm burning the fire so that I don't have to get up again in the middle of the night. That usually gets the greenhouse through the rest of the night for us, at least here in zone 7 Alabama and I can get a good 6 to 7 hours of sleep. I do want to upgrade at some point to a nice cast iron stove that will do a much better job at radiating the heat.

Our cast iron Dutch West Model inside our home can almost run us right out of there some nights, it kicks butt and radiates for hours even after the fire is out. It can be 22 degrees out and we can have the house at 80 if we get it going strong. How I wish I could find a fantastic price on that same or comparable stove and put it in the greenhouse. I'd have no problem at all keeping tropicals alive and thriving all winter with that puppy.

As one poster said though, you may have more difficulty managing temperature swings with a smaller greenhouse. You'll have to use a smaller stove and that will mean frequent trips out there to check it. Your decision to go with propane is probably a better solution for your situation.

I have a 10x20 greenhouse that I've heated with wood for many years. I'm in zone 5 where it can get really cold.The stove sets on an enclosed entry porch with open windows & door into the greenhouse.The main thing is to have a good stove & good wood.Most nights I can fill it up at 11 & it has coals at 6 AM.It stays above 50 on a very cold night & much warmer in moderate temps. I keep tropicals,hibiscus & coleus over winter in there.

10x10 is pretty small for a wood stove when you consider the necessary clearances from plants, combustibles or walls....

I've been heating the house with wood for over three decades. Indeed, I actually bought a Vermont Castings stove before I inked the sales contract.... Stoves like the VC are self-regulating, in that a thermostat controls air flow into the firebox. Even though it's a "Resolute" - one of the smaller ones - it will hold a fire all night if I stuff it full. It's also an efficient burn, in that heated, secondary air is introduced to the smoke stream where it combusts. I really can't use it above 35-40 degrees, 'cause the heat output - even set low - will run me out of the house. I don't see how it would be possible to put one in such a small greenhouse as 10x10....

I can only imagine the feeling of enjoyment of staring out of your green house that is heated by a wood stove on a cold winter day.

Sounds like a nice idea, but unless you don't have things in your life like jobs, spouses/S.O's, kids, and requirement for sleep, it could be hard to maintain. Just my $0.02.

Yes but I find that if you are really invested in your plants, you end up going out to check on them every couple of hours during a weather emergency anyway. Where I live the power goes out frequently, so I just couldn't invest in anything electrical to be my primary heat source. I also don't make enough money to spend as much as propane will cost to heat my greenhouse. Luckily I live down the street from a large farmers market where vendors sell aged fire wood pretty cheap. If money is really tight I spend a couple of afternoons chopping and dragging from the forest across the street.

One point not mentioned that I got from PlantShippers post is that you can't just load a woodstove in the morning and head to work, especially if you have thermostatically controled exhaust fans to cool inside temps. The exhaust fans will suck the smoke out of the stove and fill the structure with smoke. I never used a woodstove for daytime heat unless I was there to monitor the situation.
I use woodstoves in all 3 of my greenhouses. Each has a different model stove since they are all purchased as used stoves. In my smallest structure (15x40') the chalenge is preventing overheating on many nights. With a 10x10 structure I'd look for some other means to heat.
All of the points mentioned are good points to consider and one needs to use extra care using wood, especially if you want to stack your wood inside the structure. This Spring I was surprised at my 2 A.M. loading trip to find my woodpile on fire and the greenhouse full of thick smoke. Fortunately the damage was minimal but if I had waited until 3 A.M. things would have been much different.

Have a related question about wood stove chimneys, and polycarbonate twinwall glazing in GHs.

I am planning on putting a small wood stove in my new GH, for backup heat. The roof of the GH is 8mm polycarb twinwall material. I was planning on framing in an opening for the chimney (say 16"x16") out of galvanized steel tube. This should give adequate clearance from the double wall insulated SS chimney pipe I plan on using (at least according to the chimney manufacture). And there is no combustible material near the chimney (all steel) other than the twinwall. The chimney flashing would cover the opening on the outside, and I was planning a sheet metal cover on the inside of the 16" sq opening. I am a bit unsure of how high to make the chimney above the polycarb though.

I'd like to ask a few questions of those who have been using wood (or coal) to heat their GHs:

1. Have you had any issues with embers coming out of the chimney and hitting your polycarb glazing material?

2. How high above the GH roof does your chmney go?

3. Any other stuff I should be considering?

TIA

My 20 X 30 greenhouse has a double plastic sheeting roof (inflated) so I would be even more scared of embers or hot ashes coming out the chimney. I decided to not have my chimney pierce the roof, mine goes out the end wall up near the center ridge. I have not had any issues with drawing air even with a few sharp bends in the pipe.

One mistake I made was to set my stove near the center of the space and run a long chimney all the way from the center to the end wall and then up (a bit over 3' above the ridge just because that was the length of the pipe section). With a 15 to 20 foot chimney the smoke cools down too much, condenses and drips down the front of the greenhouse on the outside front wall. Looks like a dirty diaper and smells like bar-b-que sauce. I was told that this is how they actually make liquid smoke!

Next year I plan on building a solid wall center section on the end wall and move the stove up closer to the wall, reducing the distance and eliminating the dripping.

Interesting trianglejohn. Sounds good, although I'll be interested what you report when you shorten the horizontal run on the stovepipe. That long inside run may be cooling the smoke off and causing some creosote problems for you, but it is also helping potentially on keeping hot embers from making it out the top. But it is reassuring to hear that you have not had any close calls with hot embers on your stove/GH.

I set it up that way so that I could gain as much heat as possible from the chimney but in the end the drip mess down the front wall is just too ugly and the creosote build up is too hard to clean out. So next year I have got to change things. I also want to use old wood & glass doors from Habitat for Humanity Restore (exterior french doors) and some old windows I've collected to remake the end walls. The roll up plastic sheeting doors don't seal well enough and never roll all the way up smoothly leaving me with a slanted opening in the summer. I had to build a small narrow access door off to the side in order to go in and out of the structure, rolling up the big door on a cold windy day just let too much heated air out.

My house already has Propane heat so getting the gas company to run a line to the greenhouse won't be too big a problem. I just don't want to heat a hoophouse, they don't seal up tight. When I modify it and make it more efficient then I may buy a gas heater and only use the wood heater on the mild days to save money. I like Propane but don't like the erratic price fluctuations. I have no idea one month to the next what the price will be which makes it hard to budget.

Not to high jack this post, here is my wood stove in my HF green house. Last night -2 wood stove kept it warm till wood burned out, then the 2 space heaters on low kicked on.

This post was edited by fespo on Wed, Dec 25, 13 at 8:02

Nice setup...even in a small-ish space.

WRT the stove's flue pipe, camping places sell small wood stoves designed to be set up in tents for winter camping. These tents have metal plates - I guess you could call it either a 'thimble' or a 'stove jack' - where the stovepipe goes through the tent's fabric roof. With a bit of on-line research, I bet you could source one of these.

As long as the chimney top has some sort of screening, embers or rather sparks shouldn't be an issue. With fabric or plastic, well maybe.... I've got a 6" stainless topper I'm not using since I went with a different flue pipe system.

Cheers

Going thru an endwall is so much easier in many aspects. Just frame an opening as you would for a 24" window keeping the opening as far below the ceiling as posible, yet allowing for rise above the stove pipe. Then screw a melal plate on both inside and outside; I use the alumimum panels cut from old screen doors. Cut out matching openings so you can slide a section of pipe through. I support the external vertical flue with a 3/4" vertical pipe inserted into a larger diameter pipe that is permanate in a 5 gal. bucket full of concrete. My external vertical pipes usually extend 3' above the top of the greenhouse at the exit point but not always above the greenhouse peak.

Reasons for this method are:
1. You'll not need to be concerned about issues with the opening when recovering, etc.
2. The opening will be easily accessable to close-up or work on. Consider that with most pipes you'll need to replace them at least every 3 years under most circumstances, especially if you use coal.
3. Depending on your wood you'll need to clean out the external pipe every few weeks. I just remove a few teck screws, seperate the external pipe at an elbow and lift the entire external section off by the supporting 3/4" pipe. This is much easier than climbing onto a ladder.

My stoves are all within 2' of the endwalls b/c I want to have plants in every available space. I do have a cheap fan blowing air over each stove whenever the stoves are burning. Without such a fan blowing in my 15x40' sturucture the overhead plastic would melt above the stove exit pipe.

Regarding hot embers exiting the top of the pipes- I have seen a few when stoves were burning hot but never had a problem of any damaging the plastic film in the past 20 years. Many more problems with blowing debris from trees penetrating the film, PVC pipe touching and melting the film and wear over time creating holes in film.

I'm unsure if you are still wanting ideas, but I have a VERY efficient stove idea that my husband and I will be jsinf in our Cob home and greenhouse when we sell our home and buy more property to live completely self sufficient off the grid.

In the greenhouse we are going to be building a Cob oven and integrating it with a rocket stove, this way we can heat the greenhouse hours after the fire goes out not having to start it again until we are up and about. Furthermore integrating it with the Cob oven causes the oven to burn more efficient as well as stops smoke from coming out of the oven door, not to mention being able to bake breads, cook a turkey or ham, a casserole, or even a stew. Also we will be running the stove pkpe through a warming bench made of Cob and a warming tray area, this way seedlings that need bottom heat to sprout (such as tomato plants) can get what they need. I planned it all this way so that we have a super efficient form of heating for the greenhouse, and we gain far more than one use from the small investment considering what all we will reap from it.

I really hlpe that this will help you as well as others in deciding on the most efficient and effective way to heat any space. The best part about Cob is that it is Fireproof! I do however highly recommend sealing it very well so that water beads off, as otherwise it will only last a few years. Cob Dwellings have been around for thousands of years, it was ome of the first ways to build a home amd remains the moth eatth friendly, natural, healthy, resilient, earthquake and fire proof manner of building. Cob consists of earthen clay soil, sand, and straw. You can even paint COB with one or more colors of paint made from stone, and sculpt it forming in wall shelving, wall & floor attached furniture, and you can even sculpt leaves and elaborate designs into your stove, oven, home or other.

Best,
Jewel

Hi Jewel. An interesting idea. While I am not sure of your zone and how much heating you will need to do (which may effect if these things matter), there are a couple of things you might want to consider:

You may want a switchable Y in the exhaust one leg going straight out and the other going around your benches, for a couple of reasons. First, there may be times (really cold weather) when you need to run the heat for more time than you'd want to heat the benches. Second, you may find that you need a strong draft to get a fire going, and a long flue path usually doesn't give you that. (Just like many stoves that have a lever to divert the smoke thru baffles or straight out, so you can start the fire with the straight out draft and then switch it after the fire is going.)

You also may need to do an especially good job of sealing the cob, as GHs are typically very humid. Especially in the summer when no fires are used to dry the cob out. Or perhaps you could make the cob stove movable, and wheel it out of the GH for the summer and regain the planting space.

An interesting idea. Let us know how it works for you.