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Our central air furnace/cooler (Lennox Elite CH33-42B-2F) takes 4" filters. They can work out quite expensive, so my question is, will the system work just as well if I change to standard 1" filters, or is there something else in the equation that I'm not considering? (fitment isn't an issue - I'd use a 3" blanking frame)

  • Pleated 4" filters have much more surface area than standard 1" ... I buy 3 packs on Amazon that works out to about $20ea for MERV 8. The increased price is well worth it in my opinion because there is far less dust in the house, than we had at our prior residence using 1" fiberglass doubled up. – Tyson May 22 '17 at 21:20
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    We currently have one dog, but have had as many as three at one time. The 4" (or is it more?) pleated paper filters seem to do a good job without having too high a resistance. I have read that blower motors can be burned out if higher MERV filters are employed than the blower is designed for. – Jim Stewart May 23 '17 at 9:06
  • Actually, reducing the air flow to the inlet of the furnace blower by any means, reduces the load on the motor by reducing the amount of air the fan has to move. A fan motor will overload if there is not enough restriction to air flow. – d.george May 24 '17 at 9:58
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I favor the thick filter. We have a SpaceGuard filter unit with pleated paper filters (Aprilaire No 201) and I think this yields a superior filtration without excessive restriction. I change it once a year.

The thicker filter is better if it is the right one for your unit, i.e., it is not too restrictive. Some people put a filter on which is too restrictive and this puts excessive load on the circulation fan motor. Our system has been in service for 25 years with the original blower motor.

The fan on the condensing unit quit last year and our HVAC service replaced it.

  • We have four cats, so the 4" filter gets changed out every month - at $30 each, I'd rather use a cheaper 1" filter if it will work. – PeteCon May 22 '17 at 20:45
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    There is no way a 1" filter will do the job of a 4" filter. You would be risking getting cat hair and dander on the evaporator coil. If I understand you, you think the cat hair piles up on the surface of the 4" filter and seals it, raising the resistance, even though the body of the filter is still unfilled so it is a waste to change the whole 4" filter. Would it be possible to put a thin low resistance filter in front of the 4" filter, change the thin filter monthly and the 4" every 6 months or yearly? – Jim Stewart May 23 '17 at 1:01
  • Another possibility (which has a risk) would be to use a stack of three or four 1" filters. Each month you would remove and discard the outermost one, advance the others, and put a fresh one behind. The risk is that the resistance of three or four generic 1" filters might be significantly higher than the one 4" filter designed for the unit. – Jim Stewart May 23 '17 at 9:00

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