So what size intake hole in an 8x12x8 room sealed room with a large, not biggest, large carbon filter. It really creates a huge vacuum so enough suck but how much opening for that? thanks.
I'd say the same size as the exhaust hole. Anything bigger is almost pointless because the fan is not going to be pulling more air in than it is pushing out, and it's pushing out in a 6" hole, so a 6" intake hole would work just fine
As a general rule, you need the intake to be 2x the exhaust. So, the surface area of a 6 in hole is: A=πR² The radius is always half of the diameter, which is six in this case, so R=3 A=π3² So, this would make the surface area of your exhaust about 28.3 in A=28.3 Now you simply need 2A 2A=56.3 So you will need at least 56 in surface area for your intake. Mind you, a larger surface area for your intake might allow you to run your fan quieter, and at a lower speed.
May I ask why the intake must be two times the area of the exhaust? Is it because of negative pressure? I've just not heard of this before now.
Well, keep in mind I`m assuming that his intake is a naturally aspirated type. If he had a forced draft intake, the requirements might be a little different. I would think that the primary reasons for this rule of thumb are because it ensures proper airflow, keeps temperatures down, and also puts less strain on your fan, saving you money on electricity and fan maintenance. Also to some extent, bernoulli's principal will apply. If you make the intake smaller, the same amount of air moves through that smaller hole at a faster speed. I could see this creating problems with the temperature in lager boxes with larger fans attached becoming un-even, creating hot spots. But that`s just my best guess.
Math is wrong. Not a perfect world. Mites live in ours. Micro screen will reduce air flow. Have to keep em out you know.. so ok. Thanks also..
What part of my math is wrong? I may have rounded a couple of decimal places. Please at least explain yourself if you`re going to tell everyone I`m wrong...
I think he meant that despite the math (being correct) - the world is imperfect and won't always lend itself to such simple algorithms (like reduced flow from a screen, for example)
So you account for the screen, that's all. The math is correct to determine what twice the area of a circle is, but then you may need to factor in 20% or 30% or whatever you think is needed to account for the screen. There are two schools of thought on how large the intake should be. One school is twice the exhaust (for passive intake), as Mr. Eckted said. Idea here is to make sure there is plenty of air available to the fan (in fact more than it could handle), this will ease strain on the fan motor and extend its life, as well as it probably will run quieter. The other school of thought, however, is to make the intake smaller than the exhaust in order to create negative pressure inside the grow space. The idea here is to control odor as well as possible by making sure that if there are any tiny cracks in the grow space that negative pressure will pull air in rather than allowing any MJ-scented air to escape. This puts greater strain on the fan but, the thinking goes, better to have to replace a fan a little more often than to compromise stealth. A key to Mr., Eckted's math is that you cannot take one-half of a circle's diameter if you want a hole with one-half the area, the ratios don't work like that because you are working with the square of half the diameter. In other words, two 3-inch circular holes are not the same area as one 6-inch hole, in fact it would take four 3-inch circular holes to get about the same area as one 6-inch hole. By the same token, one 12-inch hole would be way more than double the area of one 6-inch hole. To double the size of a 6-inch hole would take one 8.5-inch hole or two 6-inch holes -- before accounting for a screen.
excellent posts, guys. Glad I haven't cut my intakes yet! I was going to cut them both the same size. How would one take a carbon scrubber into account? I've got a 4" exhaust hole from a fan at 150CFM (5" to 4" reducer, unfortunately, for now) pulling through the filter - still have to determine the size of my carbon filter, but airflow should be good. I plan on doing something similar to this DIY scrubber - A lot of people on that board rave about it, I guess. From what I've seen and read it seems pretty efficient and perfect for my needs (in size and shape)
Great point Toastybiz, i should have mentioned the sizing issue as well. As far as a carbon scrubber goes, I think that I would adjust for this by using a slightly more powerful fan, as opposed to changing the intakes.
I have an MBA in Finance so I sort of did the math already.. Yes that is the right answer. And the other guy is right on too. You don't want seem to leak out the weak areas. I don't have any really anymore though.. But you are both right and both sort of wrong.. Just the facts maam just the facts..... My strain smells like a dead skunk in the desert so I am watchful.....
Who are both right and both sort of wrong? And what is "sort of wrong"? You don't say why you think so. Who is not sticking to "just the facts"? What non-facts are you referring to?
yeah I find that post confusing. Didn't you make this thread to ask a question? Why ask it if you already know the answer?