I looked up my area's average temperatures and found this: Daily temperatures rise above 85' on an average of only one day per year and fall below 23' on an average of only 2 nights per year. During the winter, the average daily high and low temperatures are 47' and 38', respectively. The summer months are equally mild, with an average high temperature of 68' and low of 53'. With this info, do I still need a complete air exchange once per minute? I've read both of your responses and now wonder if I have an exhaust fan in the upper north gable end set to come on at temperatures above 80', and have 4 automatic vents on the lower opposing side windows, as well as the screen door opened in the south side shouldn't that be sufficient airflow in my moderate climate? I'd like to stay away from the automatic roof vents because they seem to fail so quickly, much faster than the ones in the side windows. And, what temperature am I aiming for? Is about 80' good for my peppers and tomatoes and for my seedlings? I am still eating lettuce from last fall's outdoor sowing, so I don't expect to need much extra heat in the greenhouse in winter. (Sorry, I just love to brag about my winter lettuce!) Again, thank you for your advice. I just want to do this right the first time.

ive been reading this thread and i have a few ideas for you. im curious that no one has talked about lowering the grow area. i know this sounds labor intensive but without massive energy inputs, i dont see how u plan on getting temps @ 80F with the outside temps over inside temps with the addition of the 2x poly. a few feet down will help some. also, i think shade cloth is a must in this situation. not only are u trying to be under ambient but u are adding the sun's heat inputs. maybe 2x poly isnt the answer either. seems like overkill in tx anyhow. im in freezing wisconsin and i need 2x poly but in the summer, i lift the sides. which brings me to the pt that this absolutely needs some sort of upper air escape. maybe fan's at the tippy top of ur endwalls. u mentioned that u have 8x 55gal drums in the house. what temp is that water at during the daytime? vs night? anyhow, here is a totally different way to approach a solution. u mentioned that $$$ is no matter. that i dont believe but if it really isnt... lower the flooring, use radiant heating tubes in reverse, using the cooling waters of the earth. then get a big tank of CO2 with all the valves and meters to turn it on & off at the right PPM. this will do a few things for u. 1) co2 increases the heat tolerance. u can grow @ higher temps. 2) co2 is under pressure and cold as the dickens. 3) 1200ppm+ will give u exceptional growth. 4) if u use dryice (solid co2), then u will get a cooling effect off of the 'melting' as well as the gains of the co2. but not really too sure what kinda cooling u would get or how much ice u would need. it sells for about .75$/lb. and im sure there are some smart ppl on here that can calculate how much u would need. lastly, not sure why u have a greenhouse in texas anyhow? again, in wisconsin i would but im not sure about tx. froggy

Maybe the guide I link to below might be help to you? Also, have you thought about Aluminet reflective shade? From website "Its anti-oxidation coating helps to protect greenhouses like standard shade cloth, but also assists in keeping the greenhouse cool making it an excellent choice for commercial greenhouses, plant nurseries and garden centers. Aluminet is also commonly utilized as a frost protector for vegetable crops." Here is link: Aluminet Here is a link that might be useful: Cooling & Ventilation Buyer's Guide

Interesting. Based on the pictures, yes, you have installed the blade backwards (the setscrew should be the other way on the motor shaft normally). Fan blade leaves have "pitch" (angle) in order to push or pull air, in addition, each leaf has a curve (concave or convex) depending if the fan is to push or pull. The picture seems to show the curve of the blade leaves are designed for pulling of air. So when you flip the blade, (as shown on the pictures) and the motor is rotating CCW, the air is being pushed efficiently out. Before you flip the blade, the air was still being pushed out, except the push was very inefficient because the curve was the wrong way. It appears that the blade is made for a fan intended for pulling air for a motor running CW, as in airplane engine, which is not very common. ItÂs possible that in the factory things got mixed up. dcarch