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Community and Q&A

Clogged furnace filter air restriction

Alan B | Posted in Mechanicals on

I remember reading an article not too long that mentioned a test and after 5 years there was not much change in reduced airflow from a clogged filter, but i can’t find the article for the life of me, i believe it was on GBA.
Sound familiar to anyone?

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  1. GBA Editor
    Martin Holladay | | #1

    I don't remember such an article on GBA.

    It's hard to generalize about furnace filter clogging rates. I think it's fair to say that a furnace filter will clog faster if a house is dusty (which might be the case if a house is located next to a gravel road, or in a polluted urban area), or if construction work (drywall finishing) is ongoing, or if residents bring in lots of dirt from gardening activities or firewood handling, or if the family has many dogs and cats.

    A furnace filter may remain clean for a long time in a house with one or two elderly residents who are meticulous housekeepers.

    Some furnace blowers can't respond well to a clogged filter, so airflow rates are quickly reduced by a clogged filter. On the other hand, furnaces with ECM blowers can respond to a clogged filter by increasing the blower speed, maintaining furnace performance at the expense of increased electrical usage.

  2. Alan B | | #2

    It must have been elsewhere, it was an article where the writer had set up some equipment and tested the pressure drop caused by the filter gathering dust but could not measure much restriction after several years.
    If i find it again i will post it

  3. Nick T - 6A (MN) | | #3

    I have a pressure gauge across my filter at home, it most definitely changes with dust accumulation.

    I don't have the actual numbers off the top of my head - but its on the scale of say.... clean cheap pleated filter is .3"wc differential and noticeably dirty is .4"wc... I change it every 1-2 months during heating or cooling seasons since they are <2$.

    My guess is the person was measuring the power consumption on a non-variable speed fan (old style, non-ECM) - expecting energy to go up when dirty (as people often state...).

  4. Alan B | | #4

    Very interesting thought, i had forgotten about that feature

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