Barrel stove in a greenhouse

[Ashkapp]

I’m using this stove to attempt to keep my greenhouse above freezing. It is essentially a barrel within a barrel.
It drafts good and keeps a fire going pretty well, but although the metal would get very hot it didn’t seem to radiate as much heat as I thought it should.
I lined the bottom and back with firebricks. A friend told me this defeats the purpose of the double barrel and is blocking the heat. Is this true?
It also has this a big circular opening on top- you can see the inner barrel. What is this for? I put a big cast iron pan on it for more thermal mass and same friend said that wasn’t helpful, that the hole is intended to have an elbow pipe and blower. It has a blower motor on the bottom of the stove but the wiring is cut. And I don’t really have electricity out there but could run a cord if it really improved its efficiency.
I would appreciate anyone’s experience with such a stove. It’s a big greenhouse and am only heating it March-May. I’m not expecting citrus 🙂 just trying to have maybe thirty degrees above outside.

 

[jjam]

I’m using this stove to attempt to keep my greenhouse above freezing. It is essentially a barrel within a barrel.
It drafts good and keeps a fire going pretty well, but although the metal would get very hot it didn’t seem to radiate as much heat as I thought it should.
I lined the bottom and back with firebricks. A friend told me this defeats the purpose of the double barrel and is blocking the heat. Is this true?
It also has this a big circular opening on top- you can see the inner barrel. What is this for? I put a big cast iron pan on it for more thermal mass and same friend said that wasn’t helpful, that the hole is intended to have an elbow pipe and blower. It has a blower motor on the bottom of the stove but the wiring is cut. And I don’t really have electricity out there but could run a cord if it really improved its efficiency.
I would appreciate anyone’s experience with such a stove. It’s a big greenhouse and am only heating it March-May. I’m not expecting citrus 🙂 just trying to have maybe thirty degrees above outside.

View attachment 325997

View attachment 325998

make sure your wood is dry 16% or less moisture

 

[Ashkapp]

I’m mostly burning three year old split silver maple. Interspersed with dead ash split this year.

 

[stoveliker]

do you have a flue (chimney)? None in the pic.
If a flue is present and the hole in the roof is leaky, most of your heat would fly up and out.

If no flue (see pic), none of that matters; all the heat will end up in the greenhouse (as will the carbon monoxide...)

These are quite inefficient stoves. But you also loose a lot of heat through the walls of the greenhouse.

So how do you know it's putting out less than expected (for an inefficient barrel stove)?

Of course the blower would help move warm air from the convection space between the two barrels into the greenhouse.

 

[jjam]

I’m mostly burning three year old split silver maple. Interspersed with dead ash split this year.

depending on chimney height/ but these old guys need a damper, in the stovepipe, once its going dampen it down, you could remove the brick inside / and see if that helps / but i would do the damper first

 

[EatenByLimestone]

The blower would help move the heat out. Right now its largely captured by the outer barrel. That said...

If that's a plastic sheet walled greenhouse im not sure that the blower on would be a good idea. It could act like a giant hair dryer on the plastic and shrink it to the point it tears the sheets off the 2x4s.

 

[EatenByLimestone]

How are you protecting the greenhouse from the heat of your flue?

 

[Ashkapp]

I am screwing a piece of metal to the 2x4’s, leaving the air space behind, to take the heat of the pipe. Above the pipe it doesn’t get hot.

I do have a damper. And it is 26” away from the plastic.

If I directed the heated air toward the center of the greenhouse, maybe with an elbow?, I can see the fan being effective enough to make rewiring it worthwhile.

And the firebricks? In or out?

 

[stoveliker]

If the wall thickness of the inner barrel is enough and it's in decent shape, I'd leave the bricks out.

 

[EbS-P]

How big is the green house?

 

[peakbagger]

Firebricks are going to reflect heat back into the fire and less into the building. A hot fire burns cleaner and hotter so they are both a plus of minus. The stove is heating by two different methods, convection and radiation. Convection is heated the air in the building. Heat from the barrel heats up the nearby air and it rises up. Cold air from below rises to fill in the gap where the warmed air has risen. Its called a convective loop. Radiant heat is line of sight, it goes straight from the shell to the surface its heating, if there is something in between it and the shell its blocked. Assuming the plants are sitting in horizontal trays, my guess is radiant heat would not be so good as the heat would be uneven from woodstove depending on how close it was to the stove. There really is no value in heating the floor of the building as it will conduct heat out the sides of the greenhouse so having bricks on the bottom is probably a good thing for this application.

My guess with a greenhouse is you probably want convective heating to heat the air in the room. If you didnt want to heat the air, the plants could be directly heated with an Infared heater hanging over the plants basically an infrared growlight. Since you are using wood, not so easy to get line of sight to the plants so you need to maximize convective heat gain. Air like to be laminar when its flowing past surfaces. The air layers act like layers in a layer cake and limit heat transfer to the air. In order to make the heat transfer you need turbulent flow where the air on the surface of the stove is stirred up. A big fan on one end of the stove blowing the air across the outside of the barrel will make air flow more turbulent, it will also push the warm air around the room better. Alternatively, what many wood furnaces do is build a second shell around the barrel and put a fan on the cold air end and blow air into the space between the inner and outer barrel and then duct the heat to coldest part of the greenhouse. It will setup a convective loop to heat the building more evenly.

There is also a durability aspect, barrel stoves are not thick and the bottoms tend to fail if they are not lined.

 

[stoveliker]

Firebricks are going to reflect heat back into the fire and less into the building. A hot fire burns cleaner and hotter so they are both a plus of minus. The stove is heating by two different methods, convection and radiation. Convection is heated the air in the building. Heat from the barrel heats up the nearby air and it rises up. Cold air from below rises to fill in the gap where the warmed air has risen. Its called a convective loop. Radiant heat is line of sight, it goes straight from the shell to the surface its heating, if there is something in between it and the shell its blocked. Assuming the plants are sitting in horizontal trays, my guess is radiant heat would not be so good as the heat would be uneven from woodstove depending on how close it was to the stove. There really is no value in heating the floor of the building as it will conduct heat out the sides of the greenhouse so having bricks on the bottom is probably a good thing for this application.

My guess with a greenhouse is you probably want convective heating to heat the air in the room. If you didnt want to heat the air, the plants could be directly heated with an Infared heater hanging over the plants basically an infrared growlight. Since you are using wood, not so easy to get line of sight to the plants so you need to maximize convective heat gain. Air like to be laminar when its flowing past surfaces. The air layers act like layers in a layer cake and limit heat transfer to the air. In order to make the heat transfer you need turbulent flow where the air on the surface of the stove is stirred up. A big fan on one end of the stove blowing the air across the outside of the barrel will make air flow more turbulent, it will also push the warm air around the room better. Alternatively, what many wood furnaces do is build a second shell around the barrel and put a fan on the cold air end and blow air into the space between the inner and outer barrel and then duct the heat to coldest part of the greenhouse. It will setup a convective loop to heat the building more evenly.

There is also a durability aspect, barrel stoves are not thick and the bottoms tend to fail if they are not lined.

I believe this is a double walled barrel, hence the fan and the second hole on the top

 

[EatenByLimestone]

That looks like singlewall pipe. Code requires 18” to combustible materials like plastic and wood. You’ll need a larger hole than that cut into the wall. Also, pointy end down on pipe. Right now, any creosote dripping down the pipe will make its way outside the pipe as opposed to dripping back down into the stove.

 

[peakbagger]

I believe this is a double walled barrel, hence the fan and the second hole on the top

Oops I missed that, so that means a mostly convective stove. My guess is the refractory on the bottom is not a bad thing and hotter fire probably offset the covered over surface area on the bottom.

I would consider ducting the coldest corner of the greehhouse to the fan air inlet and consider a Tee on the air outlet to spread the heat around.

 

[begreen]

I am screwing a piece of metal to the 2x4’s, leaving the air space behind, to take the heat of the pipe. Above the pipe it doesn’t get hot.

I do have a damper. And it is 26” away from the plastic.

If I directed the heated air toward the center of the greenhouse, maybe with an elbow?, I can see the fan being effective enough to make rewiring it worthwhile.

And the firebricks? In or out?

That's a meltdown waiting to happen. Stove pipe should not go through a wall, especially not a plastic wall.

 

[Ashkapp]

How big is the green house?

30 x 32 and about 14’ tall gothic

 

[Ashkapp]

Firebricks are going to reflect heat back into the fire and less into the building. A hot fire burns cleaner and hotter so they are both a plus of minus. The stove is heating by two different methods, convection and radiation. Convection is heated the air in the building. Heat from the barrel heats up the nearby air and it rises up. Cold air from below rises to fill in the gap where the warmed air has risen. Its called a convective loop. Radiant heat is line of sight, it goes straight from the shell to the surface its heating, if there is something in between it and the shell its blocked. Assuming the plants are sitting in horizontal trays, my guess is radiant heat would not be so good as the heat would be uneven from woodstove depending on how close it was to the stove. There really is no value in heating the floor of the building as it will conduct heat out the sides of the greenhouse so having bricks on the bottom is probably a good thing for this application.

My guess with a greenhouse is you probably want convective heating to heat the air in the room. If you didnt want to heat the air, the plants could be directly heated with an Infared heater hanging over the plants basically an infrared growlight. Since you are using wood, not so easy to get line of sight to the plants so you need to maximize convective heat gain. Air like to be laminar when its flowing past surfaces. The air layers act like layers in a layer cake and limit heat transfer to the air. In order to make the heat transfer you need turbulent flow where the air on the surface of the stove is stirred up. A big fan on one end of the stove blowing the air across the outside of the barrel will make air flow more turbulent, it will also push the warm air around the room better. Alternatively, what many wood furnaces do is build a second shell around the barrel and put a fan on the cold air end and blow air into the space between the inner and outer barrel and then duct the heat to coldest part of the greenhouse. It will setup a convective loop to heat the building more evenly.

There is also a durability aspect, barrel stoves are not thick and the bottoms tend to fail if they are not lined.

Thank you for being so descriptive. I think you’re right about the fan too.

 

[Ashkapp]

Oops I missed that, so that means a mostly convective stove. My guess is the refractory on the bottom is not a bad thing and hotter fire probably offset the covered over surface area on the bottom.

I would consider ducting the coldest corner of the greehhouse to the fan air inlet and consider a Tee on the air outlet to spread the heat around.

When you say a Tee- is it like an elbow? It measures 9” -can I get a stovepipe elbow in that diameter?

 

[peakbagger]

I may have confused you. The stove has pictured has a large diameter outlet in the top center which presumably is the hot air outlet while the inner barrels exhaust flue from the fire goes up and out of the building. Many of the subsequent posts arein regards to the stove flue(chimney) while my suggestion for a T was on the heated air outlet of the stove in hope that it increases the air dsitribution.

 

[Ashkapp]

I may have confused you. The stove has pictured has a large diameter outlet in the top center which presumably is the hot air outlet while the inner barrels exhaust flue from the fire goes up and out of the building. Many of the subsequent posts arein regards to the stove flue(chimney) while my suggestion for a T was on the heated air outlet of the stove in hope that it increases the air dsitribution.

Yes I would definitely try that if it didn’t require a fan. And if it did I might still do it! Thank you for clarifying. I’m attaching the inside of the barrel. And the pipe going through the double walled poly is also doubled and it gets warm but not hot.

 

[EbS-P]

How many pounds of wood are you burning a day? My guess it that you need like like 8-9 pounds per hour to get 31-41k btus

 

[Newbie78]

Even I can see many issues with that install, and

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[3650]

Very sketchy setup. Having said that I would remove the fan if you're not going to plug it in. You'll get more cool air drawing through the bottom and out the top . Ideally I would run the fan. Seems to me firebricks would create a hotter fire. However they are not necessary as long as you have a few inches of ash or sand in the bottom. Personally I think this set up is wrong in every way but to each his own. I have, out of necessity, had sketchy setups.

 

[Ashkapp]

How many pounds of wood are you burning a day? My guess it that you need like like 8-9 pounds per hour to get 31-41k btus

I’m not used to weighing the wood I use but I’d have to guess I’m using more. And I only really run it at night or on cloudy cold days.

 

[DonTee]

The Amish around me all have woodstoves in their plastic covered greenhouses. They use the square Amish made insulated chimney to go through the wall or roof. I haven’t seen one go up in flames. Yet…

I haven’t seen one with a barrel stove. They usually have the old smoke dragon woodstoves that you can get for free or cheap. The idea is just to keep the plants from freezing at night. If you can do that it should solar heat during the day.