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

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.

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

Having filters on yor ducts will effect your systems performance. If need be change your regular filter more often 4 times a year maybe.

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...

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!

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.

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.

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.

Pat

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.

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.

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 :)

I have an unframed filter with a fuzzy side and a smooth side. Which side faces into the duct? Thanks!

^^

#fuzzyontheinside

I think it's a great idea to have filters on each c.a.r. This will allow you to use a better filter (smaller micron/higher merv) without restricting the airflow to the blower fan, due to having a much greater filtering surface area. Consider the filter area at the return, 25" * 16" for example, then consider the total area you would have by adding the surface area of all return grills together. You can make a u-tube manometer in order to test the negative pressure inside the blower compartment without any filters installed, determine how much pressure difference is acceptable to you due to restriction from the filters, then install your filters and compare pressure readings.