cat box ventilation fan

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Old 11-01-16, 11:00 AM
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cat box ventilation fan

I have figured out what to do with nasty cat smells, but I need advice on a quiet 4" fan that I'll most likely let run 24/7, in a dryer exhaust flex pipe, that will be ducted in through to the attic. I'm thinking a 12 volt PC cab. fan. I don't want it so the air is pulling so hard, the cat will not wanna get into it. Just a gently, slow air exchange. So anyone with experienced with CFM, DB and durability of a fan, I'm listening and thank you. DM
 
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Old 11-01-16, 12:25 PM
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Hi DM. Whole house ventilation is a requirement from many of the modern tighter homes and target spots like a litter box can benefit from the fresh air.

One concern I see with your proposal is the duct through to the attic. You need to continue the air flow to the outside as adding moisture into the attic during the cold weather is especially bad. In addition, the metal duct will be subject to condensation.

Here are some thoughts. A radon mitigation system involves a smallish fan designed to run 24/7 and is typically located at the other end which would reduce or eliminate any noise. Those fans are not as inexpensive as what you are suggesting but would last a long time and allow adding other sources to the air flow.

As for the amount of air, my guess would be something in the range of 10 to 20 cfm. Purely a guess, but a small bath fan will move 50 cfm, way too much.

That will get you thinking.

Bud
 
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Old 11-01-16, 01:16 PM
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You can buy "computer type" fans in almost any CFM rating you desire. They also come in several different voltages. I have two in my crawlspace, fitted into one of the ventilation openings, that I have connected to a time clock. They run from midnight to four AM and again from Noon to four PM. As I recall they are rated at about 100 CFM each. I have had these in service for at least three years with no problem.

One place (there are many) to buy these fans is Marlin P. Jones Associates, MPJA.com Generally speaking, the more CFMs the louder the fan and ball bearings will generally last longer but are somewhat noisier than sleeve bearings.

I would recommend using a 120 volt AC fan just to eliminate the need for a DC power supply. Here is the page at MPJA for AC fans. AC Axial Fans | MPJA.COM I have no connection to MPJA other than as a multi-time satisfied customer.
 
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Old 11-02-16, 02:33 AM
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D.C. Fan

Thx for recommend. However I'll do a dc axial fan with xformer ball bearings, around 75 cfm. Less electricity and quieter. Thinking I'll need to get some filter on inlet side to keep the urine fumes from gooping up the hose and fan over the life of the project
 
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Old 11-02-16, 05:16 AM
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75 cfm is 4500 cubic feet of air per hour. For a 1,500 ft² home that would replace all of the inside air (12,000 ft³) every 3 hours. That's a ventilation rate for the whole house. If this is a bathroom (say 100 ft² or 800 ft³) then just 10 cfm (600 ft³ per hour) would exchange all of that air in just over an hour. If this is a mostly enclosed litter box your kitty will need a seat belt at 75 cfm.

Also, note that attic air exits to the outside in the winter but some of that air flows back into the house in the summer, called reverse stack effect.

Even occasional use of a bath fan at 75 cfm can cause mold issues in an attic.

Bud
 
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Old 11-02-16, 05:29 AM
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How much cfm needed?

Thx for that info. Not sure what cfm I can find for a gentle draw of air. Don't want the cats spooked from going in because of the draft going into the box. Found a computer place with 4" case fans all the way down to 9cfm.
 

Last edited by drmax; 11-02-16 at 05:44 AM. Reason: Wording
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Old 11-02-16, 05:42 AM
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You should be able to find a smaller fan, I've seen them glued to the top of a microprocessor chip.

At the link Furd posted I found this one at 9 cfm. Not necessarily the right one but an example of lower air flow.
12VDC, 2in. Square X 3/8in. T&T Box Fan | MPJA.COM

You might also shrink the dryer exhaust flex pipe to a 1.5" pvc pipe or even lighter material as used in a central vac system.

Bud
 

Last edited by Bud9051; 11-02-16 at 06:01 AM. Reason: correction
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Old 11-02-16, 05:47 AM
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The length of flex hose, whatever I use will most likely be about 4'. I suppose 9cfm would be enough to pull the air that distance. Really unsure. Want to order the correct one, 1st time.
 
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Old 11-02-16, 06:06 AM
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A "gentle airflow" will not prevent odors from a litter box permeating the house.
As said, the low negative air pressure will be easily over come by occasional bathroom fan use, the opening of an outside door or drafts from the cat entering or exiting the box.

The real problem is the fact that the litter is not being changed often enough allowing ammonia levels to build up in your home to intolerable levels.
At one time litter was commonly changed when solid waste built up to reasonable level.
Lately it seems that litter sifters has cat owners thinking that litter has a near unlimited life as long as you don't see any poop.
If solids build up cats at some point will look for an alternate bathroom site but it seems that they can tolerate much higher ammonia levels than what people can.

It is theoretically possible to put together a high volume/low noise exhaust system with use of a larger fan and bigger duct work but changing litter every day or two is a better solution.
 
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Old 11-02-16, 06:09 AM
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Not sure how to compensate for the exhaust duct length and size but it will reduce the flow. Add in some loss for the filter you propose and I'm guessing a 20 cfm fan would yield about half of its free air rating which should be more than enough. All you need is a negative pressure inside the box to keep all air flow headed out.

That link is a good start and there should be many more on the internet. As for picking one over another I like Furd's link and his advice.

Bud
 
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