More passive intake, or should i get some PC fans.

Just got done building my new cab. Lot of work and a bit of a headache went into making this fit my needs. I am waiting on hydro supplies and the cabinet will be holding 2x 5gal dwc buckets.

But the reason I am here is because with all of the light I want to have running in there, it is pushing my temps up to almost 100. I have a cheap bathroom exhaust fan running all hours that the lights are on. The holes in the sides are the only passive intake I have besides cracks in the door near the hinges.

My question is this: will 2-4 intake computer fans help enough to drop my tempts down nearly 25 degrees? Or should I upgrade my exhaust.

You need exhaust, and Dont exhaust back into the same room the grow box is in because then you are recyling the same air....You are heating that air exhausting it back out then passivly sucking it back in heating it further and so on til you have a snow ball effect.... You Should exhaust all air from the cab to someplace else like outside, attic, out window whatever you have to do.... Keep your passive intake and ditch your bathroom fan for a 4"inline fan and some ducting..

Your temps inside the cab will always be hotter then the ambient temps around the cab(unless you have a/c). So if the temp in the room is 80 then your cab will always be hotter then that and if your just recycling the same air in the room your temps will increase even more... Thus creating the situation you speak of with 100 degree temps

How much did you spend on all those lights all togeather lights fictures cords? Also how tall is that cab? WxL?

I figure that I have spent around $80 on the lights and the fixtures. I had all of the electrical hardware sitting around the garage. The actual grow space in the cab is 20"d/35"w/55"h.

http://www.plantlightinghydroponics.com/active-air-165-cfm-in-line-duct-fan-p-2755.html how does this look? With a little work I will be able to vent this fan out a window.

The cabinet is in a closet with no ventilation except for into the drop ceiling. I think that is my main issue. But I have no problem upgrading my exhaust.

Thanks for the response Foot.

That fan is the active air by hydro farm there cheap and load but it will diffenetly get the job done...I use that exact one on one of my grows....

bring in cool air from out side the room, use another bathroom fan as an intake bring in cool air from out side the room, and yea try and exhaust out of the room, cut a hole in the ceiling its simple to do and simple to fix...

swaggersDlite said:

bring in cool air from out side the room, use another bathroom fan as an intake bring in cool air from out side the room, and yea try and exhaust out of the room, cut a hole in the ceiling its simple to do and simple to fix...

Click to expand...

You dont need an intake fan......

Thats similar to the grow box that I am setting up. Although I am speaking with little experience I believe yes you do need intake and exhaust fans. Reason being is because you will recirculate the hot air and never maintain temperature in the grow room. For my setup I have a lot smaller of a box growing dwarf plants but I have two computer fans one intake and the exhaust with a tube running out the window. What I've noticed so far with the temperature is once you get it air tight so the only places it draws air from is the intake, and the only place it expells it is through the exhaust tube the degree regulates itself as long as the room your intake in stays cool. Now if you dont have AC and or your household stays very warm I would suggest running an intake tube out the bottom of the window and the exhaust at the top (heat rises). I am actually thinking of doing this myself. The only extra step (other than the tube installation) would be to install and maintain an air filter on the intake tube. From what I've heard if you intake air from outside you dont want fungus etc getting in.

you can put a heppa filter piece at the end of your intake, ive even heard people using nylon pantyhose at the end of it, intake's an outtake vents are always a good idea...

Surprisingly no one picked up on those tiny peep holes you call passive intake ! lol
No offense.
You need to drill larger holes and cover them with a filter, like the large, inexpensive blue filters that don't have a frame and you can cut to fit.
Got mine from Wally World, but Lowes and HD have them too (see pic).
I sit them (2) on the floor and lean them against the 2 open, passive intake flaps on my tent.
My negative pressure keeps them stuck to the side of my tent even when I open the tent door.

Anyways, check the info below and hit me if you have questions.






---------------------------Calculating the passive intake.-------------------------

The Home Ventilating Institute recommends one square foot of open air inlet per 300 CFM of ventilation fan capacity.

If you were going to use 256 CFM, you’d want 256/300 square feet of intake area, which is 122.88 square inches.

Here are some options for the intake area for a 256 CFM ventilation fan:

1 hole - 12.5 inches in diameter.
2 holes – 8.84 inches in diameter.
3 holes – 7.22 inches in diameter.
4 holes – 6.25 inches in diameter.
5 holes – 5.59 inches in diameter.
6 holes – 5.11 inches in diameter.


Here is how to calculate the hole sizes:

1. Take the total area in square inches needed, in this case 122.88 square inches, and divide by the number of holes you want.
2. Then divide by Pi (3.14).
3. Take the square root of that value.
4. Then multiply by 2.

The answer is the diameter that each hole would need to be to make up the total area needed for intake.

A large number of small holes will create more backpressure than one large hole of equivalent area. This would be negligible unless you’re using a huge number of holes or you’re using ducting to supply the air to each intake hole. If you’re just cutting them in a wall you should be fine using 8 or less holes without having to take into account the extra backpressure.

I've had PC fans burn out due to to much power. I've been having trouble as well as to heat / temps if its possible to rig a thermostat to the fans or something I'm not sure its a head ache. PC fans work great if you can get them rigged right.

i poop on PC fans........ get a real fan