what is the maximum number of 1000 watt sodium vapor grow lights that can be vented in series?

All of them.

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i am trying to connect three maximum, but am not sure if there is a possibility of overheating/heat cascading

I don't know. But just guessing I would say as many as you like as long as the heat is sufficiently being evacuated from the desired area and that the heat isn't so great that it causes premature heat failure to the extraction fan. I assume you will be using an inline fan. Of course you know these fans work better when pulling air, so it may be subject to excess heat. Something to consider would be figuring out how much volume there is in your desired enclosed reflector, and how many you want to use. You will also have to take into consideration what size pipe you will use.
volume in cubic inches= lxwxh
then divide this total x 5 to = cfm
(cubic feet per minute)
to figure out the cfm rating of your required fan. I would use the next strongest fan to be safe.
I am a licensed Journeyman Plumber (unlike "Joe the Plumber" what a dipshit) and I have to figure out shit like this for my job all the time. Good Luck.

I THINK I GOT WHAT YOU ARE SAYING,,, LIKE AFTER EACH ONE WOULDNT IT BE PICKING UP HEAT FROM THE LAST ONE AND SO ON UNTILL WHEN ARE YOU BLOWING STRAIGHT HEAT FROM ONE TO ANOTHER....

Yes, the temp coming out of 3 1000w fixtures can be pretty warm. I don't think the heat from say the first fixture would go into the second as long as your fan was strong enough. But more important is to keep the piping above the lights as heat naturally rises.Installing an open system would help by pulling cool air from another room to mix w/ hot air to cool air b4 going thru fan.

Venting of air cooled hoods can be accomplished in many ways that will produce the results you are looking for. Some important things to keep in mind are that you will want to have as cool of air as possible at your intake location weather that be inside the room with a carbon a scrubber at inlet if your ambient room temps are low enough or ouside the room at a cool location, 65-70deg would be good if possible. Also u want to have as large a diam ducting with as few bends as possible in the ducting and any that you do have are smooth and not sharp 90deg turns, if you can have it were when your lights are at the height they are at most with the ducting going straight through the room, you will remove the most heat.

Inline a/c's also help increase the number of lights to be able to string together. But ultimatly it's best to start with a quality 8 or 10 inch inline fan hook up three and see what your temps are at the outlet and work from there. You can always add another inline fan to boost the output, and I'm not talking about a booster fan but a inline fan. Hope this helps

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Each light should just be Y'd to a single exhaust and then the inline fan pulls on the end of the single vent. So each light will draw in cool air and feed it all to the y for extraction by the fan. Basically you will have 3 vent hoses y'd into a single. Problem of pulling the hot air from one across the others only compounding the heat problem has now been solved.

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Nodrama, that would necessitate more ducting, with more bends in it, and so more resistance on the fan, decreasing efficiency. The key is to have the air moving quickly enough that it is able to absorb the heat through a larger volume of air, for a lower increase in the temperature of the air.
It made sense in my head, I swear, looking at it now I'm not sure I explained as well as could be done. But it's as much as I can do in this condition, sorry!

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Originally Posted by ceestyle
Don't be a martyr wasting $100 or more on CFLs to prove they're inferior for flowering pot.