Best air filter for heat pump? Is a high MERV too restrictive?

If you want good filtration and low pressure drop, you gotta go to 5" deep filters. I personally love Healthy Climate filters MERV11 & MERV16. I use the MERV16 as it has ridiculously low pressure drop and I can get 2 years out of one easy due to all the pleats/surface area.

If you are using 1" filters, forget about it.

If a 1 inch thick filter, yes, consider a MERV 4 non-pleated fiberglass spun filter made by Flanders - a high MERV 1-nch thick pleated filter can increase total external static pressure ((TESP), i.e., resistance to air flow, to such a degree that it reduces air flow through the ducts or places additional “strain” and power consumption on the blower motor - potentially shortening its life (depends on whether you have a PSC or EMC blower motor). As far as the HVAC manufacturers are concerned, the purpose of the filter is to protect the equipment, not improve IAQ for the occupants.

But as stated if your air handler or air return grills can accommodate a thicker filter, then a higher MERV pleated filter, MERV 8 or higher is perfectly acceptable. But many air handlers-furnaces or air return grills can only accept a 1 inch thick filter.

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So our return air can only handle a 1” filter. I have a MERV 11 on it now. It is loud and sounds restrictive for sure. Our dog is already non- shedding and we don’t deal with allergies too much.

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With filters in grills, there is no point in getting high filtration filters. there is so much volume in the return between the filter and the air handler that any restriction causes air to be sucked in through cracks in the walls such that you get MORE unfiltered air than filtered air. For return grills get the MERV rated fiberglass filters mentioned above. You can get some MERV 4 fiberglass filters that do well and dont restrict much.