08:56AM | 08/09/07
Member Since: 08/08/07
1 lifetime posts
I have a 3 ton unit outside and a 3 1/2 ton in the attic. We recently replaced the attic unit from 3 ton to 3 1/2. Now the air return filter makes a whistling noise and the unit seems to be sucking so hard that the filter itself is bending. (We use pleated filters) The Return size we have now is 16X25 which is only 400 Sq in. I have been told that it should be larger but the area the return is in now can't go any bigger so we have to put an additional return in. Any suggestions on the sizes? Is the general rule of thumb 144 sq. in per ton? And is that per ton from Outside unit or inside unit. (The outside unit is only a 3 now but eventually will be a 3 1/2. Approx. 1500-1650 sq living area in home

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07:39PM | 05/25/13

Did you ever get an answer form anybody? I have a similar question:
My furnace has a large 'hammock' filter. It takes about 2 years for me to see any dirt at all. It's made from the disposable 1″-thick spun fiberglass. (I realize that I may not have had it cut to the exact correct size and shape.) I'd like to replace it with something like the Disposable Pleated option shown above. I can easily cut a slot in the main return and slide in a common off-the-shelf filter.

Question is: Can I do that? The filters don't say anything about the amount of airflow they are designed for. (cfm?) How can I know that I won't be over-taxing my system?

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