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Exhaust Fan or Roof Vent?

Posted by billsbayou 9 (My Page) on
Fri, Nov 12, 10 at 11:55

I'm building a 12x12 greenhouse. I'm putting in a 24" exhaust fan in the gable opposite to the two 16" shutters next to the door. I'm building this thing based on my own plans:
(the plans have changed a bit to make the roof higher to accommodate the larger exhaust fan)

Here's the big question:
Do I need roof vents if I have a thermostat controlled exhaust fan?

I only have access to corrugated poly panels. I'd love to get the twin-wall poly if only to make vent construction easier. I just can't figure out the construction of the vents.

Any close-up photos of vents made with corrugated panels would be GREATLY appreciated. I guess I'm looking for an excuse not to put them in if I don't know how to build them.

Follow-Up Postings:

RE: Exhaust Fan or Roof Vent?

Roof vents, unless they are very large, are far inferior to a good exhaust fan. And you won't use them at the same time. A good exhaust fan is one that will exchange the air in the greenhouse once each minute. This will hold temperature rise in the gh to ~15F above outside. So it will still get pretty hot compared to outside. Vents will likely allow the gh to warm up closer to 30F at times. With no vents a gh will warm to 50F or more above outside...yikes on a hot day!!

RE: Exhaust Fan or Roof Vent?

It occurs to me that if I were to have a power outage that the vents won't work in the Summer. However, that's usually only short-lived and during thunderstorms when the sun is hiding.

Thus, I've gone with a 20" variable speed fan and two motorized shutters from ACF Greenhouses. Link at the bottom of this message. I also bought a circulating fan and the 50' wiring kit from ACF.

Here is a link that might be useful: ACF Greenhouse Ventilation Page

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