Joe, I have been thinking about the same thing. This is what I do, I call my BIL, who is not working, and ask him to go out to check the temperature and open the doors if it is above a certain degree. I am sure that doesn't help, but it is my easy solution.

On a more serious note, are you talking about this time of the year or during the spring? I have found out that even on really sunny days during the fall, it doesn't heat up that much in the tunnel. I am ok with it getting a little warmer than desired, why, I think it is better to warm the soil and have that keep the night time temperature higher too. If I vent, I will lose this heat. Maybe I am out of my mind, but it has been working for me since early October.

In the spring, you have to vent. The suns angle is different and it does heat up more in the spring. I am wondering about installing a small fan in each hoop building with a thermostat. It won't vent it tons, but it will help.

I am in the same boat as you, I teach, so I am gone by 7:15. I would suggest that you have different levels of venting. Open the door, open two doors, small vents in the corners, finally roll up the sides. When I open a door, I always open the door opposite the prevailing wind for that day. Wind out of the north, open south door and vice versa.

In the fall, I don't see rolling up the sides as a viable option, but opening a door is probably enough to regulate the temperature. I wondered about rigging up a timer and spring system to open up a door. I would unlatch the door in the morning and have some sort of winch, attached to a timer, to turn on at a certain time to pull the door open. Don't know if it would work, but it would be simple. Probably would look like some Ruby Goldberg machine.

Jay

I know a few people that are not working or work at night. So that may work and be the best option.

I am still thinking about an auto vent. Kinda cheap at @ $50 or so. They only open a foot . Use it on a sidewall.

http://www.superiorautovents.com/Superior_Autxv.html

Last spring (our first spring with greenhouse) we just opened the 1 and only screen door (covered with plastic). I had a therometer that recorded highs and lows. There was days that my tomatoes/peppers survived in 112 degree temps with no damage. I always watered deeply after any of those days. In the mornings I would open the door even if it was 40 degrees and closed it after I got home in the evening. It worked for me and I hope it works this next year.

What size is your greenhouse?

My greenhouse is a plastic covered car canopy 10x20. Not very big, but it was a start. I'm considering adding an additional house, I'm not sure how big I can afford. We framed in the canopy that we had and then covered it with plastic taken off of a commercial greenhouse. The plastic had to be removed due to rust, we just used the clearer part and double layered it. Unfortunately we tightened it too tight to use the blower that was being throwed away. My son works for a big greenhouse and we are lucky to receive their 'throw aways'.

We have a front and rear door on our 14x24 greenhouse. We also have roll-up sides. Fortunately for us my wife doesn't leave work until 8:45 a.m. so she can open the greenhouse before work. The spring can be some of the hottest conditions in the greenhouse. Fully closed it can easily reach 110+ degrees which is not only bad for the plants but for people. With roll-up sides we can roll the sides part-way if unsure of weather conditions and leave one door open. It all depends on the sun, not so much the temp. But if the temp is going to be high just leave everything full open . . . plants can take the cold better than heat.

PS: Some vegetables will not fruit if the blossoms are affected by extreme heat during pollination. It's better to be on the cooler side than the hot side.

I agree on the sun, as I said before. When we had our freak snowstorm in early April this year, I actually had to vent by opening the door. It was 110 inside with snow on the ground outside. I have a picture somewhere. I didn't vent all day, just a couple hours.

Joe, keep in mind the sun when deciding to vent also, I will look into those vents you told me about.

Jay

We framed in a second screen door, just never installed it. If it had got hot enough for more than just a day or so, I would install the door. We got lucky since we had a cooler spring/summer. We also have trees that leafed out by the warmer time of the year. LUCKY.

I bought my hi tunnels from farmtek, and I bought a set of roof vents for each, somehow the springs in them open on thier own when the temps get to hi. I guess it is some version of metal contraction and expansion with temps. I installed an 18"x18" vent on oppisite ends about 10 feet in on each side. My tunnels are 35 feet x 96 feet, I think I may need a couple more sets .
Josh