Size matters? Air ducts in light reflectors

[RandyL]

I look at all the light reflectors on the market in catalogs, and I noticed that they have 4 inch, 6 inch, or 8 inch holes for air cooling of the lights.

I imagine an 8 inch would be needed if you had one duct running through 4-5 1000 watt HPS lights, but what about the 4 and 6 inch sizes?

I've got 2 ventilated reflectors, one runs a 1000 watt bulb and the other a 400. I may get a third for my next grow and run 3 400 watt lights instead.

I'm wondering how much of a difference in cooling efficiency there is between a 4 inch and 6 inch. Yes, there is more airflow, but is it really needed to make a difference? Or can a 4 inch flow enough?

I've got a 450 cfm barrel fan (furnace fan) drawing air through the light reflectors and pushing it out a 6 inch duct to a window fan to get the heat out of the apartment.

 

[RandyL]

Re: Size matters? Air ducts in light reflectors.

No one knows about this?

 

[SnowBender]

Re: Size matters? Air ducts in light reflectors.

Noise from a 4" will often be louder, if that's a concern.

How long is the ducting run?

 

[ozric420]

Re: Size matters? Air ducts in light reflectors.

From what I inderstand is that for 1000w bulbs u should use 8 inch for better air flow, the 4 or 6 for smaller bulbs, I believe 8 inch will work better for u. just a thought. peace

 

[RandyL]

Re: Size matters? Air ducts in light reflectors.

Overall length of my hot air out duct will be 20-25 feet.

Right now the 4 inch duct runs about 10 feet from the lights into the exhaust fan, and from there it is 6 inch duct for another 15 or so feet to the window fan, which blocks the ducting from being seen from the outside. And when turned on, the window fan helps with the exhaust air being pulled out of the room.

 

[SnowBender]

^^^^ Then I would go with at least 6 inch ducting.

 

[TorturedSoul]

Solid ducting, such as single-wall vent pipe, will tend to be quieter than the flexible stuff. In terms of absolute airflow, it will also be less restrictive. It is also fairly inexpensive (cheaper than double-wall) and easy to wrap with insulation than the flexible stuff (IMHO).