cfm air replacement fans

[donnam]

I was curious as to whether or not it would be of any benefit to get a squirrel fan at 1200 cfm for my vent hood and then a higher fresh air replacement fan at a higher cfm such as 1800 or is that overkill? How about a 1000 cfm vent and 1200 replacement?

Thanks!

Donna

[Dale M.]

I was curious as to whether or not it would be of any benefit to get a squirrel fan at 1200 cfm for my vent hood and then a higher fresh air replacement fan at a higher cfm such as 1800 or is that overkill? How about a 1000 cfm vent and 1200 replacement?

Thanks!

Donna

IF you do proper calculations of what vent hood plus duct work requires (CFM) and you have adequate large opening for make up air (open door or window) there is no need for powered make up air... Most you will do is cause so much turbulence in studio that you may actually reduce ventilation efficiency...

There is at some point you can over do things and cause less efficiency in system....

Dale

[MikeAurelius]

Yeah, I agree with Dale - fresh air should be passive - let the system draw the air it needs, especially if you are in a part of the country that needs the outside air to be heated or air conditioned. You don't want to be pumping too much outside air inside.

[donnam]

Ok, maybe I had better give you a few details...I will be in our basement. My husband has it divided into 4 separate spaces with walls. The area I will be in is about 13 X 11 at the front of the house and it only has one small rectangular window (slides open to one side). My husband was going to pipe in air from the back of the basement from the rear of the house (same side as my workshop) using a squirrel fan and ducting to get it into the room where I will be working otherwise there will be no fresh air replacement within the room itself.
I am going to have him build a vent hood with baffles approx 42w by 30 d by 30 h and vent it out of one side of the basement window. I want to make sure I have enough replacement air as I saw a thread somewhere that talked about sucking too much air away from the gas heater etc without adequate replacement which caused problems.
Thank you both for your help. It is much appreciated!
Donna

[Dale M.]

As long as make up air path has little restriction (static pressure) the opening should be at least same size as actual vent duct to outside or larger.... If you want to bring air in for fresh air circulation in other rooms its ok, but you have to consider if you are using a 30X42 inch hood, that calculates out to about 9 sqft (30x42=1,280 / 144 = 8.75) opening and at a rate of (minimal) 100 cfm per square foot of hood opening, you need a 900-1000 cfm blower... And considering room is only about 1,144 cubic feet, you are going to be changing out room air about every 1.5 to 2 minutes... Since you are going to use window as out bound vent its not going to be able to be used for fresh air source unless you duct exhaust up and away for window (at least 10 feet outside).. IF you want to bring in fresh air why not use "large passive" duct and let exhaust blower in studio power whole system... Its a lot easier to suck air out than to push air in...

Remember you need to calculate all aspects of vent system, numbers and flow rates I use in this example may not actually be accurate enough to base system on, these are just general calculation based on basic numbers you have provided.

Dale