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Greenhouses & Garden Structures

Venting and exhaust fans

15 years ago

IM building my greenhouse. I should have it framed today. Its 10x10. My question is do I need an exhaust fan or louvered vents. Im going to have a sceen door thats hopefully bug proof. I will also place a vent on the opposite wall of my door. I will also have a ciculating fan. Im just getting started and know I do need some accessories. My main goal this year at least is just to use it for seed starts for my garden. I will and should learn about what it takes to heat and cool it along the way. Im guesssing when things get really hot here, july and august is when I would need the vents and exhaust. Is the correct. thanks

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Comments (6)

bcfromfl
15 years ago
Depending upon how well you've designed your gh, you're going to need air exchange a lot more than just July and August. If your gh is in a sunny location with no shade, IMO, you're going to need an exhaust fan.

Just a head's up: with a manually-operated system (mine is too), you'll need to rig up an easy way to switch between sealing the intake and the exhaust fan opening, and opening them up. Winter months are especially a pain, when it's cold at night...yet when the sun comes out, you need air exchange and the fan running.

-Bruce
birdwidow
15 years ago
If you are wood framing a DIY custom GH, you have options those of us with aluminum framed kit models lack, starting with the ability to frame in for a standard mushroom capped exhaust fan on the roof. A 16 inch roof fan in a 10 X 10 would out-ventillate a dozen ordinary, passive roof vents.

If you want to have some real fun with it, you could build a cupola with vented sides and the fan mounted at the top, leaving a square frame inside the ceiling, to which you could attach a foam insulated hatch cover for winter.

Lots of options for a custom build. Explore them all.
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I wouldn't vent a fan through the soffit. I've seen where people have issues with the exhaust making its way back into the attic causing serious problems with moisture. I'm not sure about using an existing vent. I guess it depends on what is already using that vent and what will happen if two items try to use the same vent at once. Then again, if only one item uses the vent, will the air move backwards through the other duct? Do you have a side wall that you can use that's not close to the soffit?
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First of all, don't vent it out the soffit. The moist air will just get pulled right back into the attic thru the soffit vents. Obviously, many here are trying to have you avoid the attic all together, and if you agree, the soffit venting idea mitigates that. Having said that, I'm not a "sky is falling" type when it comes to attic venting and mold. I presently live in a house built in 1954 and my master fan goes straight to the attic. Judging by the fans' construction and the jet plane noise it makes when I turn it on, it's been there since day one. There is not one hint of moisture or mold in that attic. I know the signs of mold, and there are zip, zero, zilch, nada...get the picture :) Here's what I would do. Send the president of the association an email confirming his "...that's what everyone does..." statement. When he responds, print it out and throw it in a file you'll never lose. Now go ahead and vent that puppy straight up to the attic and forget about it. If the you know what ever hits the you know where, you simply pull out your never lose file and smile.
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Hi Artemis, Sound like you have a set up very similar to ours. Here is what we have/had: The old stove (gone when we moved into our 1929 house) vented into the kitchen wall into a massive 12 inch diameter flue (metal flue, lined with ceramic). This flue went up the wall, through the attic, and out the roof (along with the furnace flue). When we moved in, the original stove was gone, and this flue was not hooked up to anything. The kitchen wall was repaired, and no opening to it remained. But we could easily see the flue from a crawl space on the opposite side of it. In the ceiling was a cheapo fan that vented up through the ceiling and out the roof. I would guess that yours does go out the roof, but whether or not you can reuse any of its "guts" depends on what hood you want. Ours is too narrow for a good quality hood. So, you need to get up in that attic, and count your flues! We needed to remove our massive flue (to make space for a future bathroom upstairs), and that was a very difficult and expensive proposition. I think we also removed the venting from the ceiling fan, which was not a big deal. We currently have a lovely 1955 O'Keefe and Merritt stove in our kitchen. We have no hood, and the house smells faintly of the homemade french fries I made last night. I can't wait to have a hood! We plan to put a high powered (vintage looking) hood over the stove, and vent out the roof. We don't plan on hooking up the stove pipe, because we need the wall space. If you are already hooked up to a stove pipe, and you are keeping your stove (which I would certainly encourage you to do b/c OKM's are awesome!), then you can leave that assembly alone. Just add a hood over the stove (unless the stove pipe is physically in the way). Without the stove pipe, you end up with a hole in the top of your stove from which quite a bit of heat (and odor) escapes. I'm used to it (though worried about the noxious odor--which a hood will take care of), but it does get hot! Here is my stove. The stove pipe hole is on the top left side. The old flue was in the wall behind the stove. I hope that helps a bit... Now get in that attic, and let us know what you find!
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The Air King you cited uses a maximum 250 watt lamp. So 250 watts / 120 volts = 2.1 amps. The fan motor draws 0.9 amps. Combined about 3 amps.
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tsmith2579
15 years ago
For about $50 you can buy an attic vent fan with a thermostat. Also, look at the link to a previous answer.

Here is a link that might be useful: Ventilation
brandond
Original Author
15 years ago
Ok I really like the mushroom cap exhaust idea. I just hope that I wouldnt lose to much heat in the wint with that. If I did have one of these would that eliminate needing an electric fan inside. thanks,brandon
birdwidow
15 years ago
Brandon: You would need to frame for a roof mounted fan anyway, so it would be easy enough to rig it up for a cover. A simple type might be just a piece of exterior ply with holes at the corners, to match the location of anchor screws permanently installed into the fan frame. Then just use wing nuts to hold the ply in place. Line the edge of the fame with a strip of insulating foam and when the nuts are tightened, you would get a pretty tight seal.

Or just cut a piece of 2" foam insulation to fit snugly into the fan frame and it will hold in place.

BTW: It's always a good idea to install a by-pass switch on any hard wired appliance, especially one with a built in thermostat that might turn on when you don't want it to, such as a roof exhaust fan that's been sealed for winter.
zacman44
15 years ago
I don't know if they are available for the size of fan you are thinking of installing, but you may also want to consider those self opening louvers that are used with attic - whole house exhaust fans - or other louvers that would open with the fan on and close by gravity when it is off. That would not provide the same level of winter insulation as a trap door but could be useful in addition to a winter board-up.

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