Air Cooled Hood Ventilation Questions - 4" fan with 6" hood

[osecretgardeno]

Hey everyone, I was hoping to get some advice on how exactly to run cooling on my air cooled hood... this is my first time using air cooled, so I am a super noob on this one.

I have an air cooled hood with 6" vents on it. I was hoping to utilize a inline fan I already have, which happens to be a 4" and it pulls 85cfm. I was hoping to use that fan for strictly cooling the hood.

So my question is this:

Do I run 6" ducting from outside (cool air), to the hood, out the hood then use a duct reducer at/nearby the 4" inline fan?
OR
Do I run 4" ducting from outside, to a duct reducer basically on the hood, into the hood, to another duct reducer on the other side of the hood and continue with the 4" ducting to the 4" inline fan?

Like I said, I have no experience with this so I am a bit bewildered. All questions or criticism are more than welcome

Thanks in advance for the help on this, this place is full of great people.

Peace,
-sg

 

[DiscoBiscuit]

How big is your bulb? IMO, 6" from outside to the hood intake. Reducer on hood exhaust. 4" line to the fan. Make sure your lamp socket is on the fan side of the hood.

IMO, the system should be sealed so you don't have to scrub the air. With no scrubber, the fan will work best mounted as close to the hood as possible. Directly mounted to the hood reducer would be best. The fan will suck heat directly out of the hood and push it through your 4" duct. The noise won't be as bad at the end of the line.

 

[osecretgardeno]

Thanks for the quick response DiscoBiscuit.

It's a 600W HPS.

I was planning on either sealing the system or running a seperate fan on a scrubber strictly for the scrubber, so this fan will be working strictly for the cooling of the hood.

So, if I mount the inline directly to the hood reducer (I assume you mean a reducer directly mounted to the hood and the inline directly to that?) how far will it efficiently push air through the 4" line? I would need it to push probably only 2'-3'. It would be nice to avoid the wooosh sound coming out the end of the line though.

I am also trying to utilize a duct muffler, but that may end up happening at another point.

Thanks again DB, any more opinions out there?

 

[DiscoBiscuit]

If you have a scrubber or muffler in the line, 85cfm may not be enough fan. (It might not work anyway.) If you have to use a scrubber you may have to put the fan at the end. Fans pull better than they push. I'm not sure 3' of duct would make much difference in the fan noise. Insulated duct might be quieter but it'll heat up and won't move as much air.

EDIT: With no scrubber or muffler, your fan will push through three feet of duct no problem.

 

[osecretgardeno]

There will be no scrubber on the air cooling line; it is strictly for the hood.

I guess I sort of mis-named the inline muffler muffler. It's basically just a box full of insulation / noise quieting material, that the inline goes inside so that the fan itself doesn't produce a lot of extra noise. In this case it shouldn't increase or decrease the flow of air in any way.

I had thought that the fans pull way better than push, so I will be keeping that in mind.

You mentioned insulated ducting heating up and not moving as much air? I had planned on using the insulated ducting, but I'm not sure I understand the correlation between heat and air flow. I assumed that the insulated ducting kept heat in, but I assumed that this was beneficial in my case (trying to keep the room sealed).

Thanks again, your explanations have been great so far.

 

[DiscoBiscuit]

Sheet metal duct is more air flow efficient than flex. Regular flex is more air flow efficient than insulated flex. Heated air expands. The longer it takes to exhaust heat, the more heat builds up in the grow area. I'm not saying the insulated duct won't work. If the duct insulation also heats up, it may be hurting more than helping. You may have to tweak a few things to get the best outcome.

 

[osecretgardeno]

Duh, I should have figured that out. Hot air expands!

I'm going to grab some insulated ducting along with non-insulating and see what works best for my situation.

Thanks for all the advise DB, I truly appreciate it.

 

[Jnugg]

Oversized ducting allows for better airflow...my vote is 6" insulated ducting all the way..no reducer as that will add unwanted static pressures.

 

[DiscoBiscuit]

How ya gonna hook a 4" fan to 6" duct with no reducer?