Ventilation: adding lights

I currently run 2 6" 600w XXXL hoods cooled with a 6" 450CFM vortex fan drawing air from the top of the room, pushing it through the hoods, and out through the attic. I do not use a carbon filter.

I am adding two more 6" 600w hoods. My plan was to add another 6" vortex to the system on the exit side of the new lights.

My first question is: do I need to add the additional fan or do you think all four hoods will stay cool enough with the one fan? Right now I can hold my hand to the glass for extended period of times without more discomfort than a hot sunny day.

My second question is: I already have a 4 inch ~ 150 cfm inline fan and some 4 to 6 inch adapters, will adding the 4" fan on the exit side of the new hoods help at all, or will it actually hurt my airflow?

In a perfect world I'll add the 6" and also throw a carbon filter on, but if possible I'd like to run for a bit without spending just yet.

I do have multiple duct boosters available, but in my experience those don't really do anything by themselves, perhaps with the vortex?

Any input is appreciated, I'm not in a rush to fire up the additional lights just yet

a 6" duct will only move around 120 cfm so yes your 450 cfm fan will cool them all. You need to upsize your exhaust or add a second exhaust though. One six inch exhaust is not enough.

joe macclennan said:

a 6" duct will only move around 120 cfm so yes your 450 cfm fan will cool them all. You need to upsize your exhaust or add a second exhaust though. One six inch exhaust is not enough.

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Is this based on each hood teeing into a mainline (saddle connectors or wye). What trunk size? 10"?

it's really dependent on length of runs and elbows and such. BUt yes 10" trunk would be about right reducing down a size after each six inch hood. then back up to 10" or so after the hoods for the exhaust to reduce static loss.

THis is assuming the lights are in parallel not series.

I have seen two 6" xxxls ran in series off one 4" fan cool well. I wouldn't recommend more than two hoods ran in series.

There aren't any elbows in the sense of 90 degree turns. a I have a Y attached to the blower (F*** home depot and their Wye's), from there it's about 3 ft of flex duct to each hood, then flex duct back to a Y and out the attic (10-15 ft). From blower to final exhaust is about 20 ft. Adding the two lights will add about 5-6ft.

It sounds like the 6" cooling 4 lights is a maybe and adding the 4" fan is a no.

what are your y's? 6x6x8? if so this isn't too bad but i'd still like to upsize to 10"

but four 6" xxxls into one 8" duct from a 450 cfm fan is better than trying to exhaust all of it into a 6" outlet.

the bigger your intake/exhaust duct the quieter too.

oh also if you do decide to put a carbon filter in for sure upsize it to an 8"x24 or larger.

Thanks, I was thinking 6" fan 6" accessories, but I can see how having larger exhausts would be more efficient.

static loss and back pressure. With a smaller exhaust you will be pressurizing your hoods too . and it will be louder


think of it like blowing through a soda straw...It's kinda tough...Now blow through a two inch pvc pipe...Much easier see?

The same principle applies here brother. and elbows also restrict flow, so the straighter the duct the better.

Does this make sense?

Like that stupid plastic corrugated tube toy kids blow thru and it makes noise. Lol

lol.......