Filters on cold air returns

pjb999September 12, 2006

Regular viewers will know at the moment I'm particularly interested in cold air returns, and whilst painting, I've noticed how dusty my cold air ducts are. I plan to get them cleaned (I know, it's controversial) but I can see they're dusty beyond where I can reach with my vacuum.

SInce I have a dog, I'm mindful of the fact the current CARS are floor-level and will vacuum up a lot of dust etc when system's running.

I'm wondering if pre-filters are the way to go. Granted two things - one, if they're not changed or cleaned often, they'll affect the system performance, and also, I doubt they'll be very effective unless I weatherstrip around the edges so all air runs through the filter.

Is this a good idea? Will it, for example, extend the life of the system filter? Will it help keep the ducts clean, once I've had them done?

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And, for that matter. should/can the fresh air inlet to the furnace be filtered?

    Bookmark   September 12, 2006 at 8:02PM
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I had my system designed with 1 inch fiberglass filters in every return and an "air bear" filter on AH. Air bear is due for replacement next month, I'll post the results. I can easily see the pet air and smootz that the return filters are collecting.

    Bookmark   September 13, 2006 at 8:31AM
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Filters? Must be that time of year to replace the good old hardware store filters that a horse fly can get through.

Here is a link that might be useful: Home Construction Resource

    Bookmark   September 13, 2006 at 9:19AM
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Having filters on yor ducts will effect your systems performance. If need be change your regular filter more often 4 times a year maybe.

    Bookmark   September 13, 2006 at 10:47AM
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Ok, thanks. Admittedly the filter material I was looking at for the CARs is more of the 'horse fly' variety...ok for trapping gross pollutants I suppose, like the dog hairs I'm concerned about. Certainly I'll be changing the regular filter often, and I've been thinking about the electrostatic type too - the one that looks like a regular filter but has a wire etc running off it, I don't know too much about them....same principle as smokeless chimney I suppose, anode and cathode.

Right now, apres painting, my old basic two wire thermostat's hanging off the wall, it got knocked around a few times. I have a brand-new programmable 5-wire job just waiting for me to pull the new 5-wire cable through, and since the outside temp's down to 9.5C today, I guess it's time to think about getting the furnace ready...

    Bookmark   September 13, 2006 at 4:20PM
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Consider placing filter material at the outlets.
There is a blue mesh material we found at HD that
really cuts down the dust particles. Cut and place
the material inside the duct outlet, voila!

    Bookmark   September 13, 2006 at 6:04PM
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Thanks Bushleage - what did you do with the edges? Did you add seals? My system's got the returns (I assume when you said outlets you mean the return inlets) partly built into the walls/floor so they don't seal really well, I will have to run some sort of weatherstripping along the edges of the grilles to make it meaningful, or it'll just follow the path of least resistance and draw air 'round the edges of the grilles.

    Bookmark   September 14, 2006 at 1:08PM
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to many filters on a system is not a good thing. The system is designed too run with the filter on the return or inlet side of the air handler or furnace. If you add filters on the return air grilles also, that will restrict the airflow even more which could cause problems with the unit freezing up etc.

    Bookmark   September 14, 2006 at 3:44PM
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Nothing like filtering the filter's filter so the filter doesn't collect dirt from the filters filter that was filterd.

Now, if I could only filter out what I just typed.

    Bookmark   September 14, 2006 at 3:55PM
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I usually have my son change the filters but I'm tired of waiting for him. So I hauled out the ladder and went up to the cold air return. The filter has arrows on it pointing either into the duct or out to the room. Which is the correct way? I assume into the duct as the cold air would be blowing into it. Am I right or wrong? Thanks.


    Bookmark   February 2, 2007 at 12:40PM
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If you add too much additional filter media, you will need additional return registers. This is not normally a good idea. Excess filter media restricts the airflow. It just aint right.

    Bookmark   February 2, 2007 at 1:48PM
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Filters are used on the return to protecrt the heat exchanger and AC coil from plugging with dust.
Adding filters that a system was not desiged for can choke air flow and reduce efficiency and even lead to overheating or freeze up depending on the season.
Every system should have at least a filter on the return side before the blower.

    Bookmark   February 2, 2007 at 9:41PM
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Just curious if you ever tried this out (sorry to revive a dead post) and what you thought of the results. I have the same issue with a few pets and floor level air return; I took the cover off this morning and it's pretty nasty down there. Would appreciate any further info :)

    Bookmark   February 21, 2011 at 3:14PM
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I have an unframed filter with a fuzzy side and a smooth side. Which side faces into the duct? Thanks!

    Bookmark   April 17, 2011 at 8:38PM
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