Greenhouse for vegetables in hot summer

I am thinking about replacing my portable greenhouse on the deck with permanent one that equipped with automatic fan and auto-opening windows. But as usual in my small space to put something new in I need to sacrifice something else. Only way to do it I am thinking of is replacing my net house with new greenhouse. Net house accommodates peppers or cucumbers/beets on alternative years. I wondering, how hot the greenhouse gets inside with all openings open when the weather turns 90sh? I am afraid the net house occupants will not be happy inside.

The rule of thumb I’ve seen is that one air exchange per minute will hold the temperature rise inside to 10-15F above outside. In mid summer many greenhouses hit 120. Properly designed they can be held to about the same as outside or with low dew points and evaporative cooling even cooler than outside. If light needs are low then shade cloth can make a substantial difference.

To get one air exchange per minute requires large openings up high, like 20% open, and large air intake down low. Or run an exhaust fan that will do one per minute. Exhaust fans on one end and a wet wall on the other is the most cost effective way to hold inside about like outside. It costs less than $1.50 per day to cool my 1800 sqft greenhouse. I can hold low 90s on 95+% of summer days and have had no heat stress in 15 yrs.


Do you think it is realistic to find supply for all you mentioned for smaller 6X10 green house? Do you think something like this could work?

i have a $300 10’ x 20’ metal framed greenhouse with a removable cover held on with velcro on the bottom. i remove it in the winter so i dont have to shovel but the frame stays year round. i only have a a 20in. pedestal fan in there with both end doors rolled open and it stays about 5 deg warmer when its sunny than outside. the same temps as outside on cloudy days. i replace the cover about every 3 yrs due to uv degrading at a cost of $75. not nearly as nice as what you posted but it has cost me little in the 5 yrs ive had it. i use 4 ground anchors tied to the frame to help keep it in place on windy days.

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I think that’s pretty expensive for what you get. And nearly everyone will end up covering that with shade cloth because it’s too hot.

The big question is what do you want to do with it? What crops, what time of year, and what’s your climate? Those are the starting point and then design a structure that will do what you need.

You can get a lot bigger greenhouse for your money if you do like Steveb4. The little hobby kit greenhouses are expensive per sqft and most don’t last long. A bigger steel frame greenhouse covered with poly will give much more area for the same price. And big exhaust fans don’t cost much more to run than small ones. My fans at 36 inches only need a 1/4 hp electric motor to move enough air for an 800 sqft greenhouse. Put a fan or two in a 100 sqft greenhouse and it’s not much difference in running cost.


mine also acts like a shade cloth somewhat as it has green fiberglass fliaments in it added for strength. allows like 80% light through if i read the paper work right. its a Delta greenhouse i got from Amazon. they have all kinds of sizes. mine has 2 roll up doors on each end, designed so you could drive a lawn tractor thru there. when it gets warm , i leave both ends open with my pedestal fan in the n.w corner blowing towards the other door on ocillation. works pretty good. it also has 8 small windows, 4 on each side about 2 ft. from the ground if you want even more air in there. i can remove and place the cover on it all by myself so its not a big chore. ive kept stuff growing in there up to 45 days longer than the usual end of season with no added heat.

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I use it in spring for my starters. When I started to use portable greenhouse on my deck I was working at company that had no problem with me working from home in spring, so I could manage open/close windows and operate the heater and fan. Now I work for a different company and they make us to come to the office even in pandemic time, so we can sit in our cubical doors closed and use Webex for meetings - not much different from working from home. So when I leave at 8:30 it is still very cool in the morning, but I have to open the windows and depend on the heater(on thermostat). Recently I had a little accident involving breaker went off, and I started to think it is not safe to keep the heater on when I leave as greenhouse is 1.5’ from the house wall. So the best solution for me would be 6X8 greenhouse with automatic window openers I can set some where outside so heater is not going to be that dangerous as near the house. I could also use it in fall for some crop… No use in summer. The problem is, I do not have such spot I can use. So I have to figure out an option to reuse existing space …

This is similar to what I have now. Metal frame and plastic cover. But I am looking for automatic window openers… This is the most point I am looking for a new one…

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I have a 12 x 16 metal pipe frame with 6 foot sidewalls. About 12 ft tall at peak. It’s covered with greenhouse film but has shade cloth at both ends from 6 foot up. Plastic film covers the bottom ends. I have a fan and also red shade cloth from the peak down the West side to reduce the afternoon heat. Tomatoes and peppers do very well.

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