Efficient ventilation?

[Mossmoon]

Is there a way to test the efficiency of a ventilation setup? My cabinet is 3'x3'x5', in an outdoor 8x10 shop, 400 watt HPS air cooled (6" openings)with reflector open on one end sucking hot air from room & light out to exhaust duct. Using a 6" Elicent with speed control. Running at 1/3 to 1/2 power. Passive intake with three 6" holes - short duct run out of cabinet into lean-to shed next to shop. Exhaust in upper right of cab, intake in lower left. I'm running at or above outside temps.which are approaching the 80's with high 90's in a month or two. The 3 intakes are covered with a shop vac filter duct taped on the inside of the cab. When the door is partially open there is a pretty loud whistling noise. Plants look excellent, top layer of soil dries fairly quickly. Can I expect anything better than keeping the cab close to the temp of the intake air? Also running small desk fan hung in corner of cab.

Is it necessary to filter intake air with anything more than window screen?

Can I really do any more than vent the light and circulate outside air through the cab - in other words don't expect my vent system to be a cooling system except for the light?

[theMD]

An active exhaust / passive intake ventilation system is only effective if the outside temperature is at or below ideal (about room temp or lower). The system will not effectively cool anything because you are pulling hot air from outside. It should prevent the light's heat from getting out of control, but if the outside temperature is 88F then most likely inside the box will be at least 90F. Running the light from 8pm to 8am (for flowering) will allow you to take advantage of cooler night temperatures, but don't expect an outstanding crop. If you had that box in your house with a/c it would be perfect.

[Mossmoon]

If I had the box in the house I would be living by myself !! The whole idea of the box is to not grow outside - I live in a rural area and have 5 acres BUT I also have a paranoid wife so the box in my shop is a compromise. I plan to run my lights in the evening.

Why would the plants be any worse off with box temp in the low 90's when I have grown great stuff outside with the temps anywhere from 90 to 103?

[RacerX]

I think it has something to do with fresh air & Co2, Mossman.... Indoors, without proper ventilation (or air circulation), plants seem to slow down (growth)above 90 degrees or so. I'm still learning, but tossing my .02 in on the subject. The difference in my current (ventilation) setup is that it's underground (cooler air in the basement) and I used my light cooling fan to bring air from outside the box and blowing it across the light (1000W), passively exhausting the air from the light to outside the room (3"duct). I wonder if there's a difference in the cabinet temperature based on the position of the inline cooling fan on the light. Hope I didn't confuse you.... just wanted to share on the subject.

[Mossmoon]

Hey, that's Mossmoon not Mossman! The intake air comes from an inner corner of the enclosed lean-to shed next to my shop. The shed is heavily shaded, has a dirt floor and stays maybe 5 deg. cooler that outside temps and my shop temp. I would suspect that the Elicent fan has a lot more pull than a reflector's inline fan. The Elicent pulls outside air thru the light, exhausting the box & light. The reflector glass is barely warm. The exhaust easily raises the flaps on a clothes dryer outlet about 8 feet away in the lean-to shed. I climbed in the box last night to check for light leaks. There was a real strong flow of air thru the box's intake, almost like a small fan - I don't think you could hold a candle in front of it. It was very pleasant in the box - cool & breezy (and dark!). I started 12/12 today so within 8-12 weeks I'll have my 1st indoor grow finished.

[RacerX]

My apologies, Mossmoon. No harm intended. Sounds like you're good to go. Especially since you're running the light at night. Good luck with your girls.