2 x 1000w HPS Ventilation Question

In the process of setting up my new room and just had a quick question. Plan on running 2 air cooled 1000w HPS in a row with one fan. Both hoods will be Magnum XXXL with 8" flanges. Will a 8" Max Fan rated at 667 CFM be enough to cool both of the hoods? The ducting run will be minimal, under 10' total. Plan to use sheet metal ducting for everything. From what I've been reading it should be plenty, but just wanted to get a few more opinions from people running a similar setup before going ahead and ordering it. Thanks in advance for the help.

There are a lot of unknown factors in your question including the size of your room, whether or not you are also using the fan to vent the room, how many angles in the ducting, type of ducting, addition of a carbon scrubber, and on.

It's easy to figure out. Follow the formula here:

http://boards.cannabis.com/indoor-gr...ml#post1634834

I'm going to be running a sealed room setup. The fan will only be used to cool the two hoods. Fresh air will be drawn in from outside, through both hoods, and exhausted back outside. Should be roughly 3 feet of ducting from intake flange to first hood. 2-3 feet of ducting between the hoods and another 3 feet from the second hood to the exhaust. There will be one 180 degree bend to serve as a light trap, but all other runs will straight.

I've just never fan two 1000w lights in a row before, my old setup has always been a pair of air cooled 600w each with their own fan, so not really sure how to calculate the cfm requirements for this new fan.

To start, you only need a 90 degree elbow for the light trap.

This gets a bit trickier b/c you have to know intake vs. exhaust temperatures to do the calculation. Further, if you are drawing from outside your intake temperatures are subject to change by time of day and season.

Is this the old fan from your previous setup? If so, I would start with that and a fan controller to see how far off you are - if at all. I recall reading somewhere that a good rule of thumb is to increase your fan by 100 CFM for every 10 degrees you need to lower the temp. You should try to verify this as it is hearsay. Also note that I have not had to deal with your situation directly so my comments are based on related experience and reading...

I'm going to assume you have the old fan. So, hook it all up with the existing fan. Make sure that the thermometer is not in direct light! It should be in the shade about 1/2 up the wall. Let the lights run for 1 hour without the fan. Take a temperature reading. Next, run the fan on full and take temp readings at 1, 2, and 3 hours. At 3 hours you will know how far off you are. If your temps are 10 degrees too high then get a fan with at least 100 additional CFMs. If it is 10 degrees too low then dial back the fan. Also consider getting a fan speed controller that is temperature activated, if you don't already have one.

Always overestimate your fan needs. You can always dial it back. If you are drawing air from an external source and if it is cold where you are, consider the implications for warmer weather.

I pretty much have the same setup you have except no magnums, and I have a a/c unit in the room,during summer a/c is a must,but its so cold at night right now i can get away w/ it off most of the time...but I also have a small room(5ft wide 9ft long 6 1/2 ft high needs 275cfm w/o anything added to equation)...you have to calculate how much CFM your room needs...if your room only needs say 250-500 cfm then you should be good IMO...

He's doing a sealed room so the lights run in an external loop. i.e. no exhaust from the room. Just the lights pulling from an external source. Should greatly reduce the CFM requirements. Depending in intake temps I can't see needing a 600+ CFM fan.

Thanks for the replies. I think I'll just go with the 8" Max-Fan and try it out, have a speed controller if I need to dial it down. Rather go overkill on the fan then not go big enough.

I do have the fans for my old setup, but they're only 4". I'd try out your suggestion bigsby, but wouldn't the 8" to 4" reduction make quite a big difference in the math? Thanks for the light trap tip too. I've always used 180 degree turns thinking it was necessary.

When I get this put together would anyone be interested in a DIY guide to putting together a sealed room with top drip to waste system for a couple 4 x 4 tables? Not sure if there's anything like that posted on here atm. I know I wish I had a guide to follow when I put my first one together.

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Originally Posted by gbf4ever

When I get this put together would anyone be interested in a DIY guide to putting together a sealed room with top drip to waste system for a couple 4 x 4 tables? Not sure if there's anything like that posted on here atm. I know I wish I had a guide to follow when I put my first one together.

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I'd certainly be interested. Perhaps you might do it as a build log?

I built my room from scratch with the capability to convert to a sealed room in the future. In other words, it is air tight. I would just need to add the CO2. I'm relatively new to indoor growing so I want to get a few more runs done before I make it any more complicated. But a how-to here certainly would be useful.

My greatest concern is smell. I can't have any odor as I entertain lawyers and business elites directly above on a regular basis... There is no room for error! Do you get odor with a sealed room? It should be contained right?

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Originally Posted by gbf4ever

I'm going to be running a sealed room setup. The fan will only be used to cool the two hoods. Fresh air will be drawn in from outside, through both hoods, and exhausted back outside. Should be roughly 3 feet of ducting from intake flange to first hood. 2-3 feet of ducting between the hoods and another 3 feet from the second hood to the exhaust. There will be one 180 degree bend to serve as a light trap, but all other runs will straight.

I've just never fan two 1000w lights in a row before, my old setup has always been a pair of air cooled 600w each with their own fan, so not really sure how to calculate the cfm requirements for this new fan.

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Your gonna need some type of passive vent coming back into the room adding fresh air.Sounds like a good set up.:thumbsup:

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Originally Posted by GaGrown

Your gonna need some type of passive vent coming back into the room adding fresh air.Sounds like a good set up.:thumbsup:

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No, not with a sealed room. In this case a co2 element replaces the need for fresh air. At least, this is my understanding. I'm certainly willing to be educated though!

Your right! I guess with still seeing things blurry from the damage done New Years Eve, I missed that.Remember,though..cO2 is produced in the dark cycle.:thumbsup: