Just search it and you'll find the formula. As for what brand of fan..I personally am not as big on brands as I am on saving cash. SOMETIMES, trying to save ends up costing more...but I've been doing just fine with the cheaper stuff of everything.
I find digital LUMA 600 and 1000W light kits (with cooltube, 2 bulbs, timer, yoyos..) for around $170. Have never had a problem. The bulbs they come with are no-name but work fine. I buy more no-name bulbs for $20 or $30 each and switch them out every 3 cycles. I would do that with expensive bulbs too.
I bought a 440cfm fan with carbon scrubber and ducting for $150. A couple weeks later I bought a 750cfm kit (complete) for $130. They too work just fine. The big (8"...the 440 is a 6" set-up) fan sometimes makes some noise when starting but I'm ok with noise. My 6" doesnt do the occasional noisy start-up.
A scrubber only lasts so long before you need to replace it (or replace the carbon inside). I'll probably replace mine annually. I don't think I can get the carbon and pay for shipping and come in under $100(?). It might be worthwhile for me to buy a whole new system for $130. I can use the extra fan or keep it as a backup. I can use the extra 30' of free ducting too.
So..even if I buy a whole new system every year, I'd probably get about 3 years worth (3 kits) for the price of an expensive kit..which would also need re-filling or replacing annually.
Just like the cheap light kits...I can get 3 of them for the price of one Quantam or Lumatek system. The 3 cheapos though give me a total of 6 bulbs and back-ups of everything else. That's some pretty cheap peace of mind.
There isnt a whole lot of our equipment that lasts forever. Everything is "consumable" from bulbs to carbon to pumps (I replace them often to avoid pathogens and other nasties), tubing/piping, tubs, medium, airstones..
I know a lot of that stuff CAN be re-used indefinitely but for me, who buys the cheap stuff (like DIY RDWC systems with cheap hardware store parts), I can just replace stuff before it becomes problematic.
A lot of times the cheaper alternative is not worse than it's pricey counterpart. Take for example a water cooled CO2 generator. Those are like $300. If you search the same thing but call it an inline water heater it's a hundred bucks for the EXACT same unit.
Bottles of CO2. Can be hundreds at a growshop, $100 at a welding shop...or...thirty bucks from the coca cola distributer. Actually more like 20 bucks for the bottle and 10 or 15 for the gas. SNS-217 = Rosemary oil. Sweeteners=molasses,
MOAB=MPK and MAP and B1...
Almost EVERYTHING we use has a cheaper twin and if you don't care about brand names...you can save a fortune and a lot of stress. It really feels good knowing you have extra EVERYTHING.
If every single thing in my room broke at once I could replace everything right now...and still for cheaper than I would pay for one name brand unit...which...can also fail.
So yeah...figure out the size of fan you need and start shopping. Do some research and you'll find what fits for you and for well below retail. if you're thorough and patient.
PEACE.
