I'm using a fan rated 315 CFM with a carbon filter rated 400 CFM.. can I dim the fan down to 35% with the speed controller?
I don't fully understand how CFM works with carbon filters. At 35%, the fan is only pulling about 110 CFM through the 400 CFM filter. No problem, or should I crank the fan's speed up?
I can't believe the crap info you're getting fed so far.
Always get a filter rated higher than your fan rating for best odor control! Not to mention less work for your fan to pull air thru it.
The slower air passes thru a filter the more time the carbon has to absorb odors. I got a 600cfm filter last year and plan to use it with my 400cmf fan throttled back to to 200cfm. I'll leave half the plastic wrap on so it's basically a 300cfm filter with a 200cmf fan pulling thru it.
Once it starts letting stink thru I'll wrap plastic around the bottom half and let air thru the top half for another 2 or 3 years use out of it. A year so far and it's still sitting in the box all sealed up and brand new. Decent unit too with 100% virgin Australian charcoal. My last two crops weren't smelly enough to bother setting it up.
Another issue to think about is air exchange. To say you need X number of air exchanges per unit time is bullshit.
You need to have enough airflow to maintain heat and RH at optimum levels for your plants while keeping CO2 levels close to ambient unless using CO2 supplementation. These days 400ppm is ambient.
To aid with that I have my 6" inline exhaust fan connected to a Temp/RH controller that feeds it's power to a speed controller. That way my exhaust fan only comes on when the temp or RH exceeds my settings. It's just a simple bathroom fan controller wired to a cheap heat/cool thermostat wired on the cool side then piped to the speed controller which is a self-wired ceiling fan controller. Do not use a light dimmer for speed control!
Now depending on your temps and RH you may not get enough fresh air into the room to keep plants supplied with enough CO2. For most that's not a problem as too much heat keeps their exhaust fan running all the time bringing in lots of CO2. My grow room is in a concrete bunker underground and I always need heat unless I'm running a 1000W HPS. Once it's light's out I have a heater on a thermostat to keep it from getting too cold in there. Almost the end of July and the basement outside the grow room is barely 63F and that's where my grow room draws its filtered air from. Was 85F in the house today.
Last year for almost $300 I bought a simple CO2 controller but haven't had enough spare cash to buy a tank of CO2 but still can use it to monitor CO2 levels. Found out that just burning a candle in a 500 cubic ft room can get the CO2 up over 1500ppm in 20 min if the exhaust fan is off. Sitting in the same room working on the plants for a half hour does the same! I made a couple of alcohol lamps to burn cheap methyl hydrate, aka wood alcohol, and get the CO2 well over 1500 in 10 - 15 min.
If it's cold and the exhaust fan won't kick in then I fire up that sucker to keep the CO2 up to at least ambient levels. To keep it safer I have it contained in the grow room. I have smaller ones too.
As you can see by the childish arguments hijacking your thread above this post most of these 'pros' really don't have a clue but like arguing about their own ignorance. I went back to school on my 30s for 3 years to earn a diploma in environmental chemistry so not everything I say comes out of my ass.
The thousands of hours I have well wasted growing and studying cannabis gives me confidence in sharing my knowledge as well.
Good luck with your grows and grab a few of these books while the link still works.
I found a great spot to download
FREE POT BOOKS. I downloaded a grow bible first and got lots more. Books look great and complete like the real ones I have here. No web site but just a page of links. Just right click on what you want and then "Save Link As" to download so they don't open first as some are 50+ megs. They got lots. Enjoy.
