[adventured]

Perhaps strain on the cheap box fan motor as it tries to pull its air through the filter. I've gone through a number of those style of cheap box fans over the years, any kind of long-term resistance very near the intake seems to cause the equally cheap motors harm and shorten their functioning life considerably. I haven't seen the same motor damage problem with resistance added to the exhaust side. In absence of that experience I would have guessed that similar resistance on either side would harm the junk motors all the same.

[joezydeco]

I'd agree with this.

I used to put the high-efficiency filters on my furnace, my HVAC guy said these filters are so heavy that they put a strain on the blower motor. It's better for the motor to use a plain blue fiberglass filter (MSRP $1). You're not really filtering that much out of a closed house, unless you run your forced-air A/C or Heat with the windows open.

[adventured]

I did the same thing with my furnace. Just to try it I switched to a high merv filter rating and could immediately notice the considerable reduction in air flow that it was causing (and presumably increased strain on the furnace). Seeing as it was a bit more restrictive than I expected, I ended up ditching that and going back to a weaker merv rating filter (haven't gone back to the blue fiberglass style filters, just going with a weaker merv seems to do the trick, haven't had any problems with increased wear on the furnace in the last ~8 years).

[johnbrodie]

We upgraded to a "media filter" when we got new HVAC at my house. IIRC they are 4 inches thick, which gives a lot more surface area due to the deep pleats. You can then run fairly tight filters without putting undue strain on the motor - plus they last quite a bit longer. It made a moderate difference in our house in regards to dust in the air, but we also have 3 pets and live in a very dry, dusty area.

[olivierlacan]

I'd peruse this research on High-MERV Filters and their impact on airflow and pressure instead of taking one HVAC technician's word for it: http://www.homeenergy.org/show/article/nav/issues/page/4/id/...

This graph of airflow vs. MERV rating isn't very conclusive in my mind: http://www.homeenergy.org/UserFiles/file/26-6_p34big(1).jpg

Granted there are about a million variables in all HVAC systems that could affect the results.

[joezydeco]

You know, I'm going probably believe the guy that replaces blower motors day in and day out for a living as opposed to the group that sets up a "test box". Sorry.