Question: After two months of our heating slowing down, and 
finding it was the filters, we bought a gauge for our air filter. 3 months in a row now we’ve found we need to change our filter once a month… we have 1 small dog, have the house cleaned and vacuumed every other week and live on a dead end off a dead end, backed up to a cemetery (no traffic). Why is our filter getting so dirty in just one month? Makes me feel like I should just go with disposable filters. What do you think?
In late December, our house was colder than the thermostat set point for hours. I called the oil co. for a service call. I swore up and down it wasn’t the filter, but he kept suggesting it was, and sure enough, it was - In less than a month the filter was actually sucked out of shape. I was so embarrassed! But we keep a note on the attic pull down with the date last changed so he knew I wasn’t mistaken.
The next month we changed at a month, and this past month we had the gauge saying it was time to change the filter again after a month.
Hubby buys whatever he can find in pleated at Home Depot, because we have to cut them (20 x 221/4) But the tech from the oil company used what I believe you call media filter pads.
Last month I had him buy 1 because I was going to order a case online but never got around to it. I can only tell you that he bought a 3 pk last night and it’s Natural Aire - Merv 8.
Just seems like so much dirt. Our return is in the hallway ceiling so the dog hair probably doesn’t even get up there.
That is a fairly common problem and unfortunately it is one of the weaknesses of pleated air filters. They are very efficient but their dust holding capacity is not great. Dust is collected on the surface of the filter and can quickly become a problem.
You have a couple of options.
1)Your first option is to install thicker pleated filters in the filter rack. Rather than cut them to fit you can order custom size filters. They are available from 1 to 4 inches thick. A thicker filter will last longer because there is a larger surface area to collect dust. Of course this will only work if your air handler will accept thicker filters.
2)Your second option is to switch to media filter pads. Although 
media pads are not as efficient as some pleated air filters they still do a very good job. The advantage of media pads is that they have a much greater dust loading capacity than pleated air filters. Rather than all of the dust being collected on the surface area of the filter, dust is collected throughout the entire 1 or 2 inch thickness of the filter material. Distributing the dust through the entire thickness of the filter material means the filter can remain in the system longer before having the same negative effect on air flow. The dust loading capacity is much greater.