Quote Originally Posted by bigsby
That's one way to do it. Keylime is suggesting that you use two fans - one for the light and one for the room. The fan for the light would draw external air across the fan and exit the heated air externally creating a closed loop. Note that your hood must be sealed by glass. The second fan draws from the room, scrubs the air, and vent externally as well. This is in fact the most efficient and trusted way to manage the job although if you go this route you will not need nearly that size fan to cool the light. A 400 CFM should take care of the light. You will need to calculate the fan speed for the room (see below). It is also the most expensive and requires quite a bit of ducting.

There is another ways to do this. You can employ one fan that draws air from the room, through a scrubber, across the light and exits externally. You setup in this case would look like this: scrubber > light > fan > exit. This is the cheaper (one fan, one set of ducts) and simpler option.

There are numerous variables to consider when sizing the fan. The length of the duct, the resistance from the scrubber, the cooling requirements and the size of the room. You do not need to exchange the air every 2 minutes. That is silly. Aim for air exchange every 5 minutes.

See my signature for a link to a detailed how-to sticky on fan issues. There you will find a formula for calculating fan size. Read that, work the calculation and your in business. You can post your calculation up here if you want someone to check them.
Yes, you can do it with one fan.... I have done that as well in the past. There are a couple of negatives with that system however. The clean air used to run thru the lights, will not be as cool as it would be using fresh air directly. Another thing, during lights off, when exhausting air, the air also flows needlessly thru the lights.

keylime
keylime Reviewed by keylime on . Need advice on proper ventilation Indoor 12x12x8. 1000 watt halide. What type of ventilation do i need. Well insulated room. Thanks.;) Rating: 5