Cheap Blue or White Pleated Furnace Filter?

[Mike Lamb]

Is it a myth that white pleated filters are bad for your furnace because they restrict too much airflow? I have heard this too many times so I thought I would ask.

[AHI in AR]

Some expensive types designed to be ultra effective at micro particle filtration are. But your inexpensive $3 types are effective without being too restrictive. I wouldn't use the cheapo fiberglass types unless there's no other option available.

[kurt]

There is some reasonable argument that filters don't do all that much to improve indoor air quality. Filters were originally intended to keep equipment clean; whether or not they keep indoor air clean depends on a lot of variables that the single factor of a filter can't address.

I use a cheapo fiberglass after years of using a 3M model. I don't notice any particular difference.

[AHI in AR]

You can easily see through the really cheap filters. It doesn't take too much thinking to realize that they don't trap much more than the relatively large chunks of stuff passing through them. By going to a pleated design, the surface area can be expanded and filtration effectiveness increased without reducing flow too much--but only up to a point. The really dense medium used in some filters is problematic with regard to air flow. I happen to think that some of the Filtrete filters are too restrictive unless you oversize your return(s) to allow for the reduced airflow.

[kurt]

Yep. Oversizing returns to allow substantially increased filter size is essential imho. Also, unless the entire duct assembly is sealed and gasketed correctly, any restriction translates into dust getting dragged into the return, negating most of the beneficial effects of any filter.

The only filters I've seen that improve IAQ are all HEPA bypass types, run continuously, and with engineered return location and size that allows moving the massive amount of air necessary to actually effect whole house air volumes.

[John Kogel]

Yep. Oversizing returns to allow substantially increased filter size is essential imho. Also, unless the entire duct assembly is sealed and gasketed correctly, any restriction translates into dust getting dragged into the return, negating most of the beneficial effects of any filter.

The only filters I've seen that improve IAQ are all HEPA bypass types, run continuously, and with engineered return location and size that allows moving the massive amount of air necessary to actually effect whole house air volumes.

Are you saying the electronic filters that snatch dust with static electricity are inferior?

[kurt]

No, I think they're quite effective, as effective as any mechanical filter, none of which (imho) are all that great. One of the arguments for them is they don't restrict air flow like mechanical filters (Lamb's original question).

Air flow restriction vs. filter efficiency/function is the conundrum. "Good" filters can badly reduce air flow, unless they are sized appropriately.

There isn't any conventional filter that is going to dramatically improve IAQ, conventional meaning the common (approximately sized) 16x24 type filter. If you want appreciably improved IAQ without badly reducing air flow, continuous bypass systems seem to be a good alternative.

[AHI in AR]

I think we have all seen conventional filter grills where there is a lot of residue on the inside edge of the grill behind the filter. Obviously a lot of dirt bypasses the filter itself because it fits loosely in the opening. I may be a little bit obsessive about it, but I have installed compressible peel and stick weatherstripping in this area to make sure that when I close the door on the filter it fits tightly into the opening, but not so tightly that the filter is crushed. If your intake ductwork is very leaky it won't make a huge difference. But if your return is fairly well sealed it really helps.

But back to the original question: I know that many returns which I see are undersized if you go by the book. Adding an excessively restrictive filter can create other problems -- just like you have a dirty filter.

[Hearthman]

Understand the primary function of the filter is to protect the equipment--nt your lungs. If a filter is too restrictive, the high static pressure may lead to a number of problems including burning out the motor or run cap, damage the heat exchanger, carbon monoxide, poor efficiency, higher consumption of energy, etc.

The same can happen when you have no filter or an improperly sized/ fitting one or one the correct size but the filter rack allows it to flop around causing bypass of the filter media. Aside from the adverse affects to a furnace, it will lead to clogging an attached coil, which inhibits airflow thus hindering performance. This often leads to overcharging and other silly attempts to 'fix' the problem. [:-monkeyd

I agree with Kurt to focus on proper sizing of the return (which is almost always undersized), including a proper broad radius bend, possibly even with turning vanes, properly sealed with UL 181 mastic or tape, a snug fitting filter rack properly sized and mounted and then, your filter media. The code calls for a media of 8-12 MERV rating. If you choose one, such as those 3M Filtrete that are a higher MERV (yes, I know 3M claims it is a lower Merv but they're full of crap), it may do ok when new but they will quickly load up and your static pressure will climb accordingly. When in doubt, measure the static pressure drop across a filter then across a coil ,then the total external static pressure TESP and compare to the equipment specs. ).5 wci is the most common max. TESP. Any higher and your fan curve will veer out of the room. [:-alien]

[Erby]

See floppy filters and dirty fans quite often. Can't always see the coils:

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The filter was not properly in place to filter the air, and the main blower fan blades are covered with crud, which impedes the operating efficiency of the unit. This has also usually allowed dust to come in contact with the wet air conditioning coils. Wet plus dust equals mud on the coils equals coils being partially blocked. I can't see the coils to verify this though. Have the heating and cooling unit serviced and cleaned (to include removal and cleaning of both the fan and the coils) by a heating and air conditioning contractor.

===========

It's a wonderful life we lead!

[Marc]

Understand the primary function of the filter is to protect the equipment--nt your lungs. If a filter is too restrictive, the high static pressure may lead to a number of problems including burning out the motor or run cap, damage the heat exchanger, carbon monoxide, poor efficiency, higher consumption of energy, etc.

The same can happen when you have no filter or an improperly sized/ fitting one or one the correct size but the filter rack allows it to flop around causing bypass of the filter media. Aside from the adverse affects to a furnace, it will lead to clogging an attached coil, which inhibits airflow thus hindering performance. This often leads to overcharging and other silly attempts to 'fix' the problem. [:-monkeyd

I agree with Kurt to focus on proper sizing of the return (which is almost always undersized), including a proper broad radius bend, possibly even with turning vanes, properly sealed with UL 181 mastic or tape, a snug fitting filter rack properly sized and mounted and then, your filter media. The code calls for a media of 8-12 MERV rating. If you choose one, such as those 3M Filtrete that are a higher MERV (yes, I know 3M claims it is a lower Merv but they're full of crap), it may do ok when new but they will quickly load up and your static pressure will climb accordingly. When in doubt, measure the static pressure drop across a filter then across a coil ,then the total external static pressure TESP and compare to the equipment specs. ).5 wci is the most common max. TESP. Any higher and your fan curve will veer out of the room. [:-alien]

Your expertise has a surprising reach. All the way from minute details about solid fuel burning appliances to RA restrictions vs vapor line pressures.

Marc

[Tom Raymond]

Is this return large enough?

Click to Enlarge

36.07 KB

[Les]

Dear Tom,

it obviously is horizontal when it should be vertical. rotate photo to correct the air flow.

Sincerely

les van alstine

[Awenthomas]

Hi,

Pleated air filters are the best choice, because these are more effective than electrostatic filters. Generally, Pleated filters have an average efficiency of 25-30. Pleated furnace filters include cotton, synthetic and polyester material for filtration. Some pleated filters contain charcoal or carbon to help eliminate odors in addition to filtering dust and impurities. 1 Inch pleated filters effectively remove pollen, dust, pet dander and dust mites for circulated indoor air.

Thanks!!!!!!!

[mjr6550]

I think the problem with the 1" thick pleated filters is that as dirt accumulates that become very restrictive and can effect airflow significantly. You have to change them often, which gets expensive, and nobody wants to bother.

I like the 3" to 4" wide pleated filters. Much less restrictive and better filtration.

[Scottpat]

We just tack an old bath towel over the return and spray it down with water a few times a week. Seems to work pretty dang good and it's washable![]

[Neal Lewis]

Scott, I bet that's quite a fashion statement!

[Awenthomas]

Is it a myth that white pleated filters are bad for your furnace because they restrict too much airflow? I have heard this too many times so I thought I would ask.

White 1'' pleated filters are bad, white 4" pleated filters are good.

Myths are usually discussed in the ARP section.