need an extraction fan but how big?

[Pactivist]

Hey people! I am getting ready to rebuild my room for the last time, i hope . and I am having a bit of a problem. the new room design will be 5'5" x 6' and I have a veg/clone room that is 2.5' x2.5'. these rooms are side by side and are located upstairs in my house. both rooms have a 7'9" ceiling. I plan on locating my exhaust fan in my attic, above the rooms and to vent the air out of my attic vent. odors will not be a worry but it will need to be quiet, and still be able to move enough air through both rooms to keep it fresh. so my question for all my IC friends is, how big should my fan be (cfm), what style should i use (squirrel cage, other), and lastly how do I keep it Quiet? I occasionally have unexpected visitors, and my current air system howls like a banshee. so if you can help out an old hippie, i will really appreciate it. thanks, peAce

 

[teddynugent]

There's a formula that works well to give you a real good idea of what size fan you need. Instead of typing it all out, I'll just copy and paste. This is from the GrowFAQ over at OG:

Whether at the design stage or struggling with an existing problem, the following formula can be useful in assessing your situation. Its pretty basic in terms of heat transfer but from experience has proved to be pretty accurate for our purposes.

The formula is:

Q = V x P x C x dT

where:
Q = Amount of lighting (kW)
V = Volume of air being ventilated (m3/s)
P = Density of air (assume 1.2 kg/m3)
C = Specific heat capacity of air (assume 1.02 kJ/kgK)
dT = Temperature difference between ambient and growspace air in degC

You can use this to determine what the temperature rise in your space will be (dT), or given a desired temperature rise you can use it to work out how much ventilation you will require (V)

To get from CFM to m3/s divide the CFM by 2119.

Examples
Here are some examples of how you could use the formula in three different ways, each using the same basic figures for clarity.

What temperature am I likely to get in my growspace?
Assume: Lighting = 400W (0.4kW), ventilation = 240m3/hr (0.067m3/s) and temperature of air entering room = 21degC

Q = V x P x C x dT
=> dT = Q / (V x P x C)
=> dT = 0.4 / (0.067 x 1.2 x 1.02)
=> dT = 4.87, i.e. 21 + 5 = 26degC in growspace

How much ventilation am I likely to need?
Assume: Lighting = 400W (0.4kW), temperature of air entering room = 21degC and temperature of growspace to be no more that 26degC

Q = V x P x C x dT
=> V = Q / (P x C x dT)
=> V = 0.4 / (1.2 x 1.02 x (26-21))
=> V = 0.065 m3/s i.e. 240 m3/hr

What is the most lighting I can put into my growspace?
Assume: Ventilation = 240m3/hr (0.067m3/s), temperature of air entering room = 21degC, temperature of growspace to be no more that 26degC

Q = V x P x C x dT
Q = 0.067 x 1.2 x 1.02 x (26-21)
Q = 0.41 kW i.e. 400 W

So that’s it, once you get used to using it its very simple really, Just stuff the formula and figures in a spreadsheet and let it do the work.

^^^^^Good stuff^^^^^ I hope that'll help you out.
As far as what type of fan to get, I myself like blowers. A nice quality, high CFM inline fan would work well for your application too. Are the rooms sealed off? Do you have intake and exhaust fans allready?
As for quieting the fans down, you can install silencers on the ducting. They sell them online and possibly at your local grow shop. I'm not sure about Home Depot, but you can check. You can also make one yourself. I've seen plans for them, but can't find them right now. I just looked quickly though, and will give you the link when I come across it again. If you have any other questions, or if I didn't answer these questions good enough, just let me know and I'll do all I can to help you out.
Hey, got any pics of the grow room? I'm curious to see it.

-Teddy

 

[Pactivist]

got this, think it will work?

got this, think it will work?

One Year Warranty
500 CFM
115 Volt
1/10th Horsepower
3.3 Amp
1625 RPM
Single-Speed
Mounting Bolt Pattern – 6" x 5"
Overall Size 10" x 12" x 11"
MSRP: $160.00
New Unit – Never Been Used
Model Number: 7008-6033
I got this squirrel cage blower on Ebay for $40.00 I think this will be big enough (maybe too big ) I am gonna use this fan to exhaust the air from both rooms, with this old ass house the intakes are already taken care of by the old heat vents and i am gonna circulate with a couple of oscillating fans. so will this work? how loud are these fans? and how close to my rooms ceiling does this fan need to be? in other words how far will a squirrel cage fan move air efficiently? thanks y'all and peAce

edit: P.S. the pics in my gallery are of the old room before the rebuild, I don't have my own digicam but i can borrow one, and I will post new pics soon.

 

[Guest]

Having just lost a pile of bud to mold, my sugestion is the following:

Get more fans, more exhaust, and more circulation. Hepa or similar filters on the intakes would be on my list also. The filters sure seem to help with the airborne spores and particulates. Spring is in the air along with every other mold spore and seed.

On the older houses the heat and a/c registers are usually on the floor and draw up from under the house(in my case a pier and beam setup) And although the air is cooler coming from underneath the moisture and damp air have to accounted for sooner or later. Good circulation is key.

I use canister fans myself for the longer warranty, higher duty cycle rating, higher cfm, quieter, and able to adapt directly to standard canister carbon filters without adapters or mods. Cost a little more but not much. Standard 4", 6", or 8" round flanges on both ends so you can easily put it in an inline light exhaust syatem.

If one fan is good three are better in this case.

My .02

Texas Kid

 

[billy whizz]

squirrel cages are both powerful and noisy.
inline duct fans are easier to work with quietly.
an oversized fan running at reduced speed is alot quieter than the correct sized fan running at full speed but beware - if you run a fan at reduced speed you will need a controller to do this. and if you don't have the right controller it can cause a hum nd actually end up causing more noise than it save. i believe you need a controller with a stepless thyristor to ensure stealthy ventilation, but i'm happy to be corrected on that one.
also be aware that moving air upwards is damned hard work, your fan needs to be up to the job.
mount fans on rubber bungees. if necessary, mount fan on rubber bungees inside an insulated box mounted on bungees..
and the slower air moves the quieter so if you can manage to use ducting bigger than recommended, this should help out.
making your vent system efficient will also quieten it down. for example, avoid bends of more than 45deg, ensure a straight run of duct of at least 2x the duct diameter after the fan
.02
bw

 

[Pactivist]

thanks!

thanks!

wow thanks for all the info! hey billy whiz, I was wondering what a "stepless thyristor" is? is this some kind of potentiometer or variable resistor? never heard of that before.
Texas Kid, i can sympathize man, my house is seriously old,- for example- plank walls, no insulation, and lathe and plaster throughout. my intake vents are located on the floor of the second story, and the air comes from above a false ceiling, through a closet in the bathroom. weird huh. this house used to be heated with wood only and they let the heat upstairs through these vents, and when they installed the central heat they just hid the vents, so I don't think moisture will be a problem, the air comes from inside my house.
Odor shouldn't be any problem since the air will be vented about 30' up, and we have about 20mph winds everyday(windmill anyone?). so my only real concern is having enough air, and trying to keep the noise down, but it doesn't have to be silent. again thanks.