Vent fan question

[jsizemore]

Here is one of the fans I've used.

http://www.ebay.com/itm/Jenn-Air-Ele...item19ffa242c8

It has brackets built into the design that can be rotated to fit about any mounting situation. I've worked on these in the crawlspace and basement of a few houses. 6" intake and 5" exhaust. Hooked up to a variable speed control you'll be right where you want to be.

[abunaitoo]

I think I might have found a squirrel fan.
Have to wait until Monday to pick it up.
Hope it will work.
Crossing my fingers and toes.

[abunaitoo]

Picked up the fan today.
Smaller than it looked in the picture.
Guy said it came off of a stove vent from an older house.
It feels like it sucks more than the fan I'm now using.
I'll post a picture later.

[rosewood]

Is there some kind of chart that would show the sucking CFM????
All the fans/blowers I see have only the blowing CFM.

Input = output. If it blows XX CFM, it will have to pull XX CFM. Simple fluid dynamics.

[rosewood]

Picked up the fan today.
Smaller than it looked in the picture.
Guy said it came off of a stove vent from an older house.
It feels like it sucks more than the fan I'm now using.
I'll post a picture later.

Man, I am sure glad you got a fan that sucks.

[Cmm_3940]

Based on what I've encountered when buying computer cooling fans, there's also something called 'static pressure' involved that seems only indirectly related to CFM.

[GrayTech]

Input = output. If it blows XX CFM, it will have to pull XX CFM. Simple fluid dynamics.

Due to very slight compression by the fan the in volume would be minutely larger, but that's splitting hairs....

[trapper9260]

I had set up for casting in my attic to the chimmy that can not be use for wood anymore due to age and other problems and got a bathroom vent fan from menards and a hood to hold it in place and try it out yesterday and work out just fine and no problems at all.Might have to put a dimmer switch on it to control the speed to slow it down some not sure yet about it.

[retread]

I use a squirrel cage fan from an old forced air furnace. Great for low noise and good volume.

[rosewood]

Due to very slight compression by the fan the in volume would be minutely larger, but that's splitting hairs....

This is true. However, the moles would be the same. Didn't want to make it to confusing.

[abunaitoo]

Picture of what I have.
Attachment 139830Attachment 139831

[JeffG]

Here's my setup, it does amazingly well.

[jsizemore]

Picture of what I have.


Attachment 139830Attachment 139831

That's from the good old days. I bet it's got another 50 years in it.

[abunaitoo]

I tried it today.
Made a mount to the top of the casting bench.
Formed a funnel out of cardboard.
Fan to small. Need to look for a bigger fan.
Back to the drawing board.

[mongoose33]

I tried it today.
Made a mount to the top of the casting bench.
Formed a funnel out of cardboard.
Fan to small. Need to look for a bigger fan.
Back to the drawing board.

That's the biggest problem w/ my setup--I'm just not moving enough air. I may be able to counter some of that by having a better collection hood. Here's what my current setup looks like:



I'll either make a better collection hood or, if I can find one cheap enough, use a kitchen hood like is shown earlier in the thread.

[abunaitoo]

See what you think about this.
Does the placement, of the fan in the ducting, make a difference on how much suck you have?????
Would you feel more suck, on the inlet, if the fan was father down in the ducting?????
My thinking is that the air would move faster, or smoother, by being directed through the ducting.

[mongoose33]

See what you think about this.
Does the placement, of the fan in the ducting, make a difference on how much suck you have?????
Would you feel more suck, on the inlet, if the fan was father down in the ducting?????
My thinking is that the air would move faster, or smoother, by being directed through the ducting.

Think about where you want the pressure to build, both positive and negative.

In my setup above, I don't have a completely airtight setup. Thus the fan at the outlet in the window. If I positioned the fan at the hood, any smoke it sucked up would be partially expelled at any point in the ductwork further on. Any smoke that currently gets in the duct stays there because there's a negative pressure behind the fan.

[jcren]

"Blade" type fans are very sensitive to placement. If using a duct booster, the fan should mounted at the hood for max effectiveness. Squirrel cages/centrifugal fans are closer to positive displacement and have higher suction ratings, which is why they are used in vacuums.

[skeettx]

Really, your fan should almost fill the vent stack
If not, you will create a vortex situation and the fan will not
be very effective

Maybe this one will fill the stack better

http://www.ebay.com/itm/Broan-Replac...item3aa9d1d0ce

Mike

[durango]

You guys are spending too much money on this project--its soooooo simple--use an old dryer fan!!!! You'll have to do some creative engineering for mounting etc. You'll also have to find someone who knows these motors to pick out which two of 4-5 wires to power up. The motors have several speeds and all you want is high. I built mine to an old kitchen hood for a paint booth for model railroading. For smelting, I use a blower from a furnance, sucking from the pot blowing outside with a 20" box fan blowing makeup air into the shop. Steve