?'s On Heating and Venting My GH


New member
I was planning on just using a portable propane heater with a thermostat to heat my greenhouse. However would this put off noxious exhaust that would be bad for the plants? I'm planning on venting the GH by simply using an exhaust fan set to very low speed so the air exchanges very slowly. It needs to be slowly because in the colder weather I can't be constantly pulling freezing cold air in. I was thinking that for the air intake I'll run 10 or 15 feet of duct inside the GH so that the air has a little time to warm up before it actually enters into the grow space.

Does anyone have any better ideas on how to do this?

That's the only way I can think of balancing the ventilation with the cold air problem.

The Grey Man

New member
Heat vs Air - the age old problem for UK greenhouse growers nearing the end of the season...

If you don't vent you WILL get bud rot.
I think your propane heater will be fine - you are venting anyway.
I actually like your ducting idea, to heat up the air before it hits the environ.
I may use it myself (of course, it requires electricity.)
I'm fairly sure (and this is just observational) that it was the wind and rains that limited my outdoor grows, as opposed to the cold - which some strains are pretty hardy to.
Good pruning techniques and an eye for plant-environment cleanliness will also help against rots and moulds - A LOT.

Good Luck, bro.
propane heater will make more moist, put one in little room and check the humidity getting higher,it will also make condensation under the gh
i ve the same prob when i grow under gh, you must vent them the more you can and prevent evaporation from the soil ; mulching,plastic......
pro use also this kind of thing ; hotbox sulfur burner.


New member
Damn. Condensation wasn't even something that occured to me! See this is why I consult you pros! lol

Problem with venting here is that come December we can get sub zero temps here. So it's hard to bring in air without frosting them. I imagine I'm gonna get condensation wheather I use a heater or not. We get more than 300 sunny days a year here. The sun will heat it during the day. I'm going to use a heater to heat it at night.

Grey Man- I'm going to use the clear type ducting for the heat exchange system. That way, not only will the warmer inside air surrounding the duct help heat the air flowing through it, but so will the suns rays.

I'm hoping to flower in the green house all winter long.

So aside from adding to the condensation problem, a propane type heater will work?

Mary Mary

New member
G`day BDD

Flowering when the daylength gets below 10 hours and cool temps is very slow .
Less than 11 hours and things slow down . Then add cool temps and metabolism grinds to a stop .

Where the green house shines is extending the seasons . Going into Dec / Jan or coming out of winter in March / April .

Equinox is Sept and March every year . Time your grows to have the plants flowering at those times and you get the strongest sun at around 12/12 .


New member
Ahh thank you. I've never grown in a greenhouse do this is all new territory for me. Even still if I can flower into December that would be good enough.


Well-known member
You can always extend the photo-period through artificial lighting. I've never done a greenhouse but I have done winter grows for seed runs using frost blankets when needed and supplemental lighting. Seeding is something to consider if you don't need sinsemilla ... IMO it helps plants finish with the crazy photo period stuff mid winter when days get longer. ;) so...hash and seed production crops.

too late for this season but of course more open bud structure is going to help fight rot.


New member
Put on 2 layers of plastic and pressurize the middle with a blower. It will act as insulation and will keep the temps higher and the condensation to a minimum.

Also fill plastic barrels up with water and paint them black to Absorb heat I'd go ahead and do that now so it will be holding heated water as it would take a while for the water to heat up.
I've been in greenhouses where it was extremely hot and they had black material laid down on the floor to suppress weeds but that black also made it hot.

Also forgot to add that one of those guys had black plastic lines running from his black barrels in which the water flowed through. I don't know if this helped heat the greenhouse but it was right next to his plants.


New member
Barrels would take up a lot of space in mine. I'm going to put up white opaque plasting on the inside. The clear panneling is letting in too much light I'm afraid. The greenhouse is getting really hot. I'm guessing even on a winter day, with full sunshine that baby is still going to cook.


New member
Just use clear... it's kinda cloudy & will reduce light a little anyway, but soon you'll appreciate the the heat from the sun. Greenhouses don't hold heat well. At night they release it. What was said about black barrels is right. A little tubing ran around, a sm pump from the pet shop, fish dept & you have radiant hot water heat, solar powered. I've found 5 gal jugs, flat & wide, low profile for camping. Takes up 6". I found mine in a hardware store. Paint em black, place against north wall, good to go! :)

And what Plantmanbee said about supplemental lighting too. You could go all year! :)
- I've used gauze as shading through the summer in grnhses, just tack it up for the summer on the inside, take it down for the winter. But a second layer using the clear plastic will also help insulate against excess heat.
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