Greenhouse Exhausting

I'm trying to figure out the best way to exhaust my greenhouse.

I have a 24" fan hooked up with two 20" intake shutters on motors, and am trying to decide whether to hook them up to a thermostat, de-humidistat, or timers.

Since I'm all geared up for a winter cycle (plants ready, modine propane heater, and 80 amps available for lights and accessories if needed), I was worried it might never get warm enough for a thermostat to kick on thermostat often enough to exchange there air properly. With a dehumidistat I'm afraid it will never turn off and I'll burn through a ludicrous amount of propane keeping it warm. With a cycle timer I have no idea what to set it to...

The temperature will hit low 30s to mid 20s by the end of December. Not terrible but enough to not want the fan running all night. Not to mention the exhaust fan is really loud and sounds like a jet engine in the distance (budget model).

Hope everybody ate well last night!
Any help would be appreciated.

Sorry for the typos - not sure how to edit my post

Just an idea, if it were me i would run a co2 burner(or use your heater with a y peice with a damper hooked to co2 controller if it burns clean i dont know) and only vent once when sun goes down. Maybe have it on a humidstat with low temp shut off as well depending on outside humidity.

Call around to greenhouse suppliers for ideas.

The issue can't be heat right now, but with the rise in temp you may get a rise in humidity...
now thats the real issue, give you plants some mold/bug prevention by spraying neem oil every month or so, in preparing for an early spring?
Don't be suckered into venting out of a cold day with lots of sun

ps I prefer lots of different fans in differencing positions, to give you more options

Diggaz said:

Just an idea, if it were me i would run a co2 burner(or use your heater with a y peice with a damper hooked to co2 controller if it burns clean i dont know) and only vent once when sun goes down. Maybe have it on a humidstat with low temp shut off as well depending on outside humidity.

Call around to greenhouse suppliers for ideas.

Click to expand...

The heater is 80% efficient so I'd assumer theres a fair amount of CO released. I do have an 8 burner CO2 generator I used in the past for an indoor room. After a quick google search I didn't find any dehumidistats with a low temperature shutoff. Might be able to rig one with a relay if thats the best option, but I want to see if anybody else is doing the same thing and what their solutions are first..

I've spoken to a couple greenhouse suppliers and so far nobody has been able to help. They've mostly been salesmen though

vostok said:

The issue can't be heat right now, but with the rise in temp you may get a rise in humidity...
now thats the real issue, give you plants some mold/bug prevention by spraying neem oil every month or so, in preparing for an early spring?
Don't be suckered into venting out of a cold day with lots of sun

ps I prefer lots of different fans in differencing positions, to give you more options

Click to expand...

Heat definitely isn't the issue right now, but cold and humidity are. At the moment, night temps are hitting high 30s to low 40s and 99% humidity, and its going to get colder in the coming months. No mold as plants are pretty healthy, but starting to see some aphids. The exhaust fan will drop the humidity to 60-70% in about 2 minutes, but it lets the heat out just as fast. There are HAF fans circulating the air 24/7, but adding multiple exhaust fans doesn't seem practical. This is for a mid February harvest so I can have something ready transplant by March as well.

Neem Oil foilar applied, will offer great protection against aphids, is also systemic which the plants drink up and still offer great protection

vostok said:

Neem Oil foilar applied, will offer great protection against aphids, is also systemic which the plants drink up and still offer great protection

Click to expand...

I sprayed azamax. I'm normally more on top of preventative spraying with azadirachtin but my priority has been on other things. Not too worried about aphids though.


Still nobody with experience using timers to cycle exhaust fans? I know there was a member who mentioned it in a post awhile back but I'm having trouble finding it

What size greenhouse? What is the roof like, is it pitched? You might be able to get a thermal screen.

Don't speak with Salesmen, you want head growers and technicians advice.

Ideally you want a fan in each end of the structure and up high as possible, this wants to be connected to a humidistat not timers and they will work by themselves 24/7 365 regulating the humidity to your desired specifications.

How cold is the ground and what are you growing in? Pots?

Heat rises so you could get a Hotbox Thermabed http://www.hotboxworld.com/products/hotbox-thermabed/5/cat

You want to have some oscillating fans in the Structure to move stale air about.

http://www.hotboxworld.com/products/hotbox-superb/6/cat This will be the environmental control needed