Venting fan question

[outhouseinn]

I just built a shed in an upstairs room to put all the cat pans in, keep the dogs out, keep the dust in-house down, easier to sanitize and keep clean, etc.

I put one of these dryer vent caps through the outside wall of the house and into the back wall of the shed. It has a standard four inch pipe.

Then I went looking for a four inch booster fan. I read reviews that the four inch didn't vent plant houses that well.. if it didn't vent well simply for heat, I thought it wasn't going to clear the air of dust when I am cleaning pans and such.

Then I bought an 8 inch duct booster fan

And also a 8 x 4 reducer

I put it together tonight. It seems to work fine. There is naturally some backflow.

My questions...

1) Will this strain kill the fan quicker?

2) Is it venting the dust as well as if I ignored others reviews on the fans and had bought a 4 or 6 (with 6x4 reducer)? Or is it kicking too much dust (stirring) back into the shed?

3) Would you (opinions please) go with a smaller fan? (while I can still exchange)

 

[outhouseinn]

Answered my own question for anyone interested.

In daylight you can see that the vent cap flap on end doesn't even have enough airflow to open.

Switching out for 6X4 or just 4.

 

[Sponsor]

 

[PorcelainVacation]

There are 4" duct fans designed for venting bathrooms. I would use something with at least 100cfm if I was going to rely on it for comfort while changing cat litter, that's a disgusting job.

 

[Jadnashua]

The effective air flow in a ducted system depends on several factors, which includes the CFM of the fan, the length of the duct, and that functionally gets longer with every elbow or other restriction. How 'leaky' the area is you are trying to vent for makeup air also plays a lot into it. A tight house or room, and you might try to blow a lot of air out, but will just end up lowering the pressure in the room, without much air movement. You need a free flowing air source inlet in order to blow air out of a room.

 

[Dana]

A 400cfm fan is ridiculous overkill for your application. What makes more sense is a LOW cfm low wattage/high efficiency fan that runs 20 continuously to keep the stink from building up in there. A Panasonic Whispergreen FV-05-11VK1 bath fan runs $125-145, but at low speed it's pulling only 3.5 watts (about 8% of the power of that monster duct blaster, about 30% of the 4" VIVOSUN duct fan) , and delivers up to 50 cfm at that speed (exact cfm depends on duct impedance.)

Running the Whispergreen 24/7 x 365 will only use ~30 kwh/year. At 20 cents/kwh (the CA average is 19 cents) that's $6/year, and the room stays reasonably pleasant. There is an additional cost in slightly elevated heating/cooling load, but without local climate & equipment efficiency data it's hard to say how much that would add up to.

There's no such thing as "...venting the dust..." but there is such a thing as "...kicking too much dust...". The source of dust in most houses is typically outdoor air infiltration- the tighter the house, the less dust will accumulate. A low cfm fan won't depressurize the space as much as the bigger fan, and will draw less dust in via air infiltration paths. But it will depressurize the shed space sufficiently keep dust from moving from the shed into adjacent spaces, unless you're running some monster oversized kitchen exhaust fan or something.

If you run your oversized van intermittently, only when your cleaning the space you'll have to let it run for several minutes to achieve even one air exchange, but it'll use less power and pull less infiltration dust into the house. But it won't keep dust from migrating from the shed space into adjacent spaces, since the open vent channel allows outdoor air to flow from outdoors into the shed space whenever there is wind, stack effect, or exhaust fans depressurizing the adjacent spaces relative to the outdoors, thus pulling cat-shed air and dust into the rest of the house.