A wood stove can heat a greenhouse safely if the chimney is right. Use insulated stainless Class A pipe. Take it out through a solid, framed part of the end wall or roof. Keep it clear of the glazing and end it above the ridge.
Can You Put a Wood Stove in a Greenhouse?
Yes, heating a greenhouse with a wood stove works, as long as the chimney is built for the building. A greenhouse is glazed, humid and quick to cool, and each of those changes how the chimney is routed and what it is made of.
A greenhouse wood burning stove is only half the job. The other half is the run from the stove collar to the open air: a short stove pipe in the room, then insulated chimney pipe through the wall or roof and up above the ridge.
Is a Wood Stove Permitted in Your Greenhouse?
It depends on your local code, so ask your building department before you buy anything.
There is no national building code in the United States. Codes are adopted locally, by the state and often again by the town or county, so the answer depends on where the greenhouse stands.
Take the chimney's installation instructions with you. For a factory-built chimney such as Class A pipe, the residential code clause is IRC section R1005.1: "Factory-built chimneys shall be listed and labeled and shall be installed and terminated in accordance with the manufacturer's installation instructions." Those instructions are what an inspector reads the job against.
What Is Your Greenhouse Made From?
A greenhouse is glazed with glass, rigid polycarbonate panels or polyethylene film, and plastic glazing sets how close anything hot may come. The frame behind it is usually wood, aluminum or steel.
Plastic glazing and film soften at temperatures far below those a stove and its pipe reach. A clearance written for wood framing was never meant to protect them. And a glazed wall, glass or plastic, has no framing to carry a pass-through.
So the useful question is not only what the greenhouse is made of, but where it has a solid, framed section the chimney can pass through.
Where Will the Chimney Go: Wall or Roof?
Through a framed end wall is usually the simpler route. The chimney leaves the building low down and climbs outside on solid framing, so nothing hot runs up through the growing space.
| Question | Through a Framed End Wall | Through a Glass or Polycarbonate Roof |
|---|---|---|
| Where the pipe passes | A solid, framed section of the end wall, beside the door frame or between posts | A glazed roof panel replaced with a framed, solid infill panel that carries the support box and flashing, with the greenhouse maker's approval |
| What fits the opening | A wall pass-through (wall thimble), supplied in the kit | A roof support box that carries the pipe, and a flashing with storm collar, matched to the roof pitch, that seals it |
| Pipe inside the greenhouse | A short stove pipe run to the wall | Stove pipe climbing to the roof support box, with its 18 inch clearance kept all the way up |
| Draft | Needs the full outside height, in insulated pipe | A straight vertical run, which usually drafts well |
| What to check first | Wall thickness, and that the section is solid, not glazing | Whether the greenhouse maker allows a roof penetration at all |
What Each Kit Puts Through the Wall or Roof
For the wall route, the stove pipe runs to the wall and Class A pipe takes over before it. Only the insulated pipe passes through the wall, inside the wall thimble that comes with both of our wall kits. Outside, a tee turns the pipe upward onto a base support, held to the wall with brackets.
Choose the wall kit by the length of Class A pipe the chimney needs above the tee. Our external garage chimney kit covers 4 to 19.6 feet (48 to 235 inches). Our wood stove through the wall kit covers 14.2 to 25.9 feet.
The base support and every wall bracket must fasten into solid framing, all the way up. If the end wall is glazed above the pass-through, the chimney needs its own post or framed strip to climb, well away from the panels. Our flue design service can plan the brackets and supports along it.
A roof route suits a greenhouse with a solid, framed roof section. On a glazed roof, a panel has to be replaced with framed, solid infill to take the support box and flashing, so ask the greenhouse maker first.
Where the roof can take it, our kit to vent a wood stove through the roof matches the flashing to roof pitches from 1/12 to 12/12. For a curved, flat or steeper roof, ask us before ordering.
If your greenhouse is closer to a wood shed, with solid walls and a roof, our guide to fitting chimney pipe for a shed covers that build step by step.
How Much Clearance Does the Chimney Need From Glazing?
For plastic glazing and film, more room than any clearance chart gives. The two published figures below are measured to combustible building material, such as wood framing, and neither was written for plastic. Glass does not burn, but a glazed panel is still never the place for a pass-through.
- Class A chimney pipe: 2 inches to combustibles, per the installation instructions supplied with the system.
- Single wall stove pipe: 18 inches to combustible material, per IRC Table M1803.3.4, the residential code's table of chimney connector clearances.
- Plastic glazing and film: no published figure. Keep the stove, the stove pipe and the chimney well away, and pass through framing, never through a panel or film.
Stove pipe never passes through a wall, ceiling or roof. The insulated Class A section does that job, through the wall pass-through or the roof flashing.
How High Above the Ridge Must the Chimney Go?
At least 2 feet higher than the ridge, if the ridge is within 10 feet of the chimney. That is the 3-2-10 rule of NFPA 211, which the installation instructions for our Class A pipe quote under Chimney Height.
The chimney ends at least 3 feet above the highest point where it passes through the roof, and at least 2 feet higher than any portion of a building within 10 feet.
On the wall route the pipe never passes through the roof, but the 2 foot rule still applies to the greenhouse ridge and to any other portion of a building within 10 feet. A lean-to greenhouse against a house has to clear the house roof too. Our guide to the chimney height code works the rule through with examples.
Why Is Stainless Class A Pipe Right for a Humid Greenhouse?
Because a greenhouse is damp and its chimney runs in cold air. A cold flue condenses the water in the smoke. Insulated Class A pipe keeps the flue gas warmer, which helps reduce creosote buildup and keeps the draft steady.
Our Class A pipe is double wall, with 304 stainless steel on both the inner and the outer wall and insulation between them. It is rated for 1000°F (538°C) in continuous use and sold in 6 and 8 inch. The stainless outer wall matters for a chimney that stands in the weather beside a damp building.
Inside the greenhouse, the stove pipe is black single-wall steel, not stainless, so check it for rust each time the chimney is checked.
Every length comes from the same system, so the clearances and joints follow one set of instructions. You can see the range as Class A double wall pipe by diameter and length.
What Happens to the Draft When the Fire Goes Out?
The greenhouse cools fast, the chimney cools with it, and a cold chimney pulls weakly. The next fire can then smoke back into the greenhouse until the flue warms.
Three things help:
- Keep the run straight and short inside, with as few turns as possible.
- Use insulated pipe for every length outside, so the flue holds its warmth longer.
- Build at least the height the 3-2-10 rule asks for, measured on your own greenhouse.
Watch the exhaust fans too. A running greenhouse fan pulls against the chimney and can draw smoke and carbon monoxide back into the greenhouse. When the fans run, let outside air in, or ask the stove maker about an outside air supply.
Critical Safety Rules for Smoke and Carbon Monoxide
A closed greenhouse on a cold night holds smoke and carbon monoxide close to the plants and to you. Keep the gases outside and know what to do if they get in.
- Place the chimney top away from roof vents, louvers, fans and doors, so smoke is not drawn back in when they open.
- Fit a carbon monoxide alarm and a smoke alarm inside the greenhouse.
- If the carbon monoxide alarm sounds, get everyone outside and call 911.
- Keep fuel, potting mix, film offcuts and stored plastics away from the stove.
- Have the chimney checked before each heating season and swept when soot or creosote builds up. While you burn, the installation instructions ask for a check at least every 2 months and for the cap's spark screen to be checked at least every 2 to 4 weeks.
Plan the Chimney in This Order
- Ask your building department what it needs for a stove and a chimney in a greenhouse.
- Find the solid, framed section the chimney can pass through: the end wall or the roof.
- Measure the stove collar, so the pipe matches it: 6 or 8 inch.
- Measure the wall thickness, or the roof pitch.
- Work out the height the top must reach against the ridge and any portion of a building within 10 feet.
- Choose the kit for that route and read its installation instructions before you cut.
If you would rather not work it out on paper, our flue designers will plan the system as a free flue design for your greenhouse. Pick the drawing closest to your greenhouse, fill in your measurements, and we send back a chimney configuration that fits. Or talk it through on 888-834-0880.
Need More Information?
Clearances and flue temperatures for Class A chimney pipe are answered on our questions page.
Each route is taken in order in our step-by-step stove pipe installation guides. And if you would rather go through your setup with someone, ask our technical team or call 888-834-0880.
