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After I put in a 3M filter into my furnace the air flow was massively reduced.

So, does that mean the filter is wrong or something is wrong with my furnace.

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First, does the 3m filter meet the furnace manufacturer specs? Second, do a simple test. Observe the air flow with the 3M filter in, change it out to an old filter or no filter at all. Is there a big difference in air flow? Are any of the returns covered with a carpet or other obstruction? If the no filter test greatly improves flow and there are no obstructions, you may have the wrong filter. If if doesn't improve with no filter, then call a tech and start looking at the furnace blower.

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great, thanks. I'm going to buy another filter tonight and try. I think you are right, wrong filter because without it it blows much....better (lol). But seriously, it seems like a reduction of about 40-50%. – cbrulak Jan 11 '11 at 20:49

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