2k Watt Ventilation

MrDankFace

MrDankFace

Member
I am currently running 2000w in a 14x12 room. Everything is dialed pretty good, but my temps are still in the low 80s around my canopy and I'm trying to figure out how to lower that a bit if I can.

I run 2 Blockbuster 6" Hoods with a 6" inline fan pulling and exhausting out of a window box I made. The window is air tight, except for a 6" passive hole I cut. I've sealed off all the vents in the room to prevent the heat from entering. The doors aren't completely sealed off, so there is passive air coming through them. I don't seem to feel much air at all coming through the passive hole I cut in the window box...

It's always around 81 degrees about 24-30" from the hoods (where I like to keep my canopy in flower). Even when it's in the single digits outside. I've even tried adding another 6" fan to the exhaust at the other end of the lights, but it stays the same exact temperature.

Should I add the second fan to the passive air intake I cut in the window box, with a controller set at low to keep my negative pressure? That would bring the cold air from outside in to cool down the room a little better?

I feel like I'm pulling heated air from my house through the doors and cracks in the room, but I'm not sure how I can completely seal the doors and stuff from that passive air coming through.

Everything still looks great with the temps in the low 80s, but I feel like that's a tad too high if it's something I can help. Any advice or opinions would be greatly appreciated! Thanks guys!
 
NrthrnMichigan

NrthrnMichigan

Well-Known Member
Personally I pull the air from the outside thru my light and expel into the room. My temps are controlled by a fan speed controller. So easy for me to keep my temps low. 75° and steady.
This does create some condensation but it is manageable. I'll reverse this when the outdoor temps begin to rise in the spring.

Jm .02
 
A

anzohaze

Well-Known Member
I run 1300cfm thru 2 8 inch blockbuster hoods and my hand is cool 15 inches from 1000 watt. You osciallting dans to move heat at canopy. Or put a box fan on the ground and let in blow rhrew canopy and heat will go up away from plants
 
MrDankFace

MrDankFace

Member
Yea, I have 2 oscillating fans blowing on the canopy and one underneath along the pots and whatnot so fans aren't a problem. I have a foot shorter ceiling than most people to work with, which is why I went with 6" instead of 8". I kinda wish I got them 8" anyways now, but whatever. It's working out just fine, like I said, just wish it were a few degrees cooler in the high 70s.

One thing I noticed after posting last night, warm air was coming back through the passive. The exhaust hole must not be far away enough from the passive so it was sucking some of the warm air back into the room. That probably has something to do with why I can't cool it off any. That has since been sealed off, and we'll see how much of a fix, if any, it was.

Thanks for the help regardless guys.
 
MrDankFace

MrDankFace

Member
I mean, there's no problems here either touching the glass. It's not hot to the touch or anything. Apparently there's not a problem at all, I just thought low 80s were a little warmer than ideal temps, but I guess not.
 
MrDankFace

MrDankFace

Member
NorthofEngland said:
2000w for 14 x 12ft
equals less than 12watts per square foot....?

That cannot be right.
Click to expand...
The room is 14x12, that doesn't mean I use all of it for the 2000 watts that I have. The actual light footprint and space I use for the plants is maybe 8x8 or 8x10...but for the sake of air displacement and ventilation, the actual size of the room is what matters obviously.

Everything is just fine in this garden, the only question was how to lower my temps a few degrees...which, according to my plants the past year or two, isn't needed I guess...I've just always read that 77/78 is IDEAL, so I wanted to see if anyone had any advice on how to lower that 81 a few degrees is all.
 
MrDankFace

MrDankFace

Member
NorthofEngland said:
WHAT?
Care to back up that statement with a link or a quote or anything at all???
Click to expand...
Yea, I thought I've always read and been told that your passive needs to be smaller to keep the negative pressure you want in your room but I'm not 100%.

The only reason I made it the same was because that was the only holesaw I had at the time. And it seems to work just fine, other than maybe being a few degrees over ideal. There's still negative pressure in the room.
 
E

effect

Active Member
guys guys guys, it's passive, of course it has to be bigger to not be a bottleneck. you can have it way small if you want, but it'll impede flow without an intake fan.
 
E

effect

Active Member
fir3dragon said:
Wheres the link?
Click to expand...
to common sense? hahahahaha. weed forums. what is your argument? that you don't understand hvac or can't do math? the area of an 8 inch circle is about 100", so a window of about 30" wide would need to be open 6-9", to ya know, have a chance of keeping up with the several hundred cfm of air you're ideally blasting out it. that fan is pretty windy right? it blows on your hand pretty hard? well if you don't have as much air flow coming in, you're going to have vacuum right? and how does working in a vacuum effect fan performance? it lowers performance because the air is thinner, and the fan cannot spin faster. OK, so it's sub optimal to have excessive vacuum. it'll work, but the fan is working harder for less. the 2x-3x thing isn't some forum rule some guru came up with, it's just an off the cuff figure in this case to illustrate that you need a good bit more to compensate, look up ANY hvac shit on google.

i'm not linking to anything because i wrote that myself just now as a forum contribution. you wana try it?
 
J

joe macclennan

Well-Known Member
superstoner1 said:
A passive intake needs to be at least 2-3x as big as exhaust. Low 80's is perfect, I set mine at 84.
Click to expand...
It does need to be larger...but not that much. at least 25% larger is the rule of thumb.....hvac by trade
MrDankFace said:
Yea, I thought I've always read and been told that your passive needs to be smaller to keep the negative pressure you want in your room but I'm not 100%.

The only reason I made it the same was because that was the only holesaw I had at the time. And it seems to work just fine, other than maybe being a few degrees over ideal. There's still negative pressure in the room.
Click to expand...

It will put neg. pressure on the room even if it is sized right. If you put a smaller intake in it will make the fan work harder shortening it's life, and also reducing the cooling efficiency. .

and go with the 8" for thirty bucks more it is worth it. You don't have to push your fan as hard to achieve the same results.

the magnum xxxl by sunsystems used to leak a little but the new models have been redesigned and have a stronger structure as well as extra thumbscrews on the inlet and outlet. The new ones don't leak a bit....I'm quite impressed honestly.

These things ROCK imo.
 
MrDankFace

MrDankFace

Member
effect said:
to common sense? hahahahaha. weed forums. what is your argument? that you don't understand hvac or can't do math? the area of an 8 inch circle is about 100", so a window of about 30" wide would need to be open 6-9", to ya know, have a chance of keeping up with the several hundred cfm of air you're ideally blasting out it. that fan is pretty windy right? it blows on your hand pretty hard? well if you don't have as much air flow coming in, you're going to have vacuum right? and how does working in a vacuum effect fan performance? it lowers performance because the air is thinner, and the fan cannot spin faster. OK, so it's sub optimal to have excessive vacuum. it'll work, but the fan is working harder for less. the 2x-3x thing isn't some forum rule some guru came up with, it's just an off the cuff figure in this case to illustrate that you need a good bit more to compensate, look up ANY hvac shit on google.

i'm not linking to anything because i wrote that myself just now as a forum contribution. you wana try it?
Click to expand...
I don't need a link or anything personally, I appreciate you helping out and explaining. I'll be completely honest, I don't know shit about HVAC. That's why I asked. What I've been doing has worked, it's just a little hotter than what is supposed to be "ideal" temperatures.

You're right though, it's just common sense and math LOL. With a passive intake, it just needs to be slightly bigger than the exhaust...not necessarily 2-3x...which I think is why it's working out for me ok. I have a 6" passive with 6" exhaust...but there's also passive air coming from the under the door and small tiny cracks throughout the room etc...so I actually do have more passive intake than exhaust.

Rather the way I have it would be fine if the intake and exhaust fans weren't so close together. I found that warm air that was getting exhausted was coming right back through the passive intake hole the other night. Which would probably help explain why my temps aren't where they should be.

I know what I need to do now to fix it though so thanks for the input guys.
 
jrainman

jrainman

Active Member
fir3dragon said:
Wheres the link?
Click to expand...
well Sir its much more then just a link to something , Understanding the physics of air movement

what is the actual estimated BTU Load

cubic feet of area to be exhausted and exchanged with Make up air ( well you say passive air )

The amount of air you are looking to exchange in a certain time frame (cubic feet of air per min)

when you have all this information then you can equate the proper size fan, ducting and make up air (passive air)

I have said this many times here : YOU only can move a certain amount of air through a certain size whole or duct , just because you cant see AIR does not mean it does not take up space and only so much air can travel in or through a certain area of space at a certain rate of speed. most of you have the 10 pounds of $#!!) in a 5 pound bag design. No disrespect to all . this was my field of work for 30 plus years

calculating the correct amount of air to move through a certain area is physics ,Math and understanding how air moves.

example of ducting calculation: 1,500 cfm @ .08 water per 100ft of duct (water= friction Loss )

Solution: velocity at 950 FPM (feet per Min)
Duct diameter @ 17 inches (round duct)
duct dimensions @ 20'' x 12'' or 16'' x 15'' (rectangle duct)

example of Fan calculating : current conditions - 2,500 CFM. 2'' static pressure.
800 rpm and .25 horsepower
Desired conditions - 3,500 CFM
.39'' static pressure; 1,120 rpm
.69 horsepower.
 
MrDankFace

MrDankFace

Member
joe macclennan said:
It does need to be larger...but not that much. 25% larger is the rule of thumb.....hvac by trade



It will put neg. pressure on the room even if it is sized right. If you put a smaller intake in it will make the fan work harder shortening it's life, and also reducing the cooling efficiency. .

and go with the 8" for thirty bucks more it is worth it. You don't have to push your fan as hard to achieve the same results.

the magnum xxxl by sunsystems used to leak a little but the new models have been redesigned and have a stronger structure as well as extra thumbscrews on the inlet and outlet. The new ones don't leak a bit....I'm quite impressed honestly.

These things ROCK imo.
Click to expand...
Well, it's a little too late for the 8" now, I already have four of the 6", even though I'm only using two. I do wish I had gone with 8" though, and will in the future. My friend just got a few of the new Magnums too and they look awesome. I bought the first two blockbuster 6" because I was growing in a 8x4 tent for a few years. I liked the square profile to match the tent's. Would definitely just get Magnums for a full room.
 
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