Dr. Kool‘s

Where Good Neighbors and Good Servicemen Meet

Air Filters

The Short Story

"Frugal" people try to get the most out of their air filters, but that's false economy. If your air filter gets stopped up, bad things can happen:

  • If your ducts get dirty, it could cost you big bucks to have them cleaned. Replacement is sometimes necessary, and that could run into the thousands.
  • Your condensate drain could get stopped up, and water could come through the ceiling.
  • A choked up system is hard on the compressor—they're not cheap either.
  • Finally, good filtration minimizes allergy problems, reduces dusting requirements, and lowers utility bills.

I estimate that 15% of my billing is for unnecessary work caused by poor air filtration. To minimize these problems, use good "throw away" filters, and change them on a regular basis.

  • Some filters say, "Change every 90 days." That message was not written by Dr Kool, and should be ignored.
  • You need to have clean filters in place at all times.
  • Don't hesitate to discard a filter that looks clean.

The cost of filters is minor compared to the damage that could result from poor air flow. Register on this website, www.drkool.net, and we'll remind you by email when it's time to change your air filter.

The Full Story

Your indoor air filter performs two critical functions: first it protects your AC equipment. The second critical function is to clean the air you breath—to protect your health. I will approach the subject carefully and objectively.


Early filters were little more than a metallic mesh, which would trap medium to large particles that would interfere with system operation. Those filters could be cleaned and re-used. The next generation filter was a flat fiberglass or polyester one—more effective, but not re-useable. Then came at least one experimental filter. I say experimental, because once put on the market, the filter failed the test.

The Electronic Filter

The electronic filter is theoretically the most efficient, but comes with considerable maintenance and repair problems. Unless your medical condition requires it, I do not recommend the electronic filter.

The Electrostatic Filter

It was introduced with much fanfare as a lifetime filter—they were on sale everywhere. But, with time, this filter flunked the test. The electrostatic filter trapped some pretty minute particles, but it was restrictive to air flow, and easily became stopped up. After repeated washing, some of the trappings became permanently locked in, and air flow was even more restricted. If you have one of these filters, even if you bought it from me, I advise you to discard it.

The Media Air Cleaner (MAC)

This is a 4" filter element, which you change about twice a year. It's an excellent means of filtering your indoor air. The MAC comes with none of the disadvantages of the electronic or electrostatic filters, does a good job of filtering the air, and is not restrictive to air flow. The cabinet is a fairly expensive, contractor-installed, item, and the element is not cheap. (Actually, there's a 4" element you can use in a standard filter grille, and that's not a bad approach.)

The Pleated Filter (usually 1" thick)

At this stage of filter evolution, the pleated filter seems to be the best for people who don't want to get overly fancy. As long as you diligently follow your filter change schedule, you are not likely to encounter the problems I mentioned above—dirty coil, stopped up drain, etc. Furthermore, your indoor air quality will be excellent.

The Standard Flat Filter (usually 1" thick)

This old standby will prevent dirty coils, stopped up drains, etc. but the indoor air quality will not be as good, and you should expect to dust more often. Again, you must diligently adhere to your filter change schedule.

A Word of Mouth Pages Extra

If you register as a Kool Kustomer, and check the appropriate box on the registration form, we will notify you by e-mail on a monthly basis when it's time to change your air filter. Doesn't that take a load off your mind!

Now let me qualify the notification I just offered. We offer a single notification schedule which will fit at least 90% of the population. You will be notified every month starting April 1st and going to October 1st. In cooler weather your blower runs less often, so you can skip November, January, and March. You will not be notified for those months.


If you use the 4" media filter, our notification plan is not for you. If you set your thermostat, so the blower runs continuously, you might have to (on your own) replace the filter for the months when you are not being notified. If you run a day care center, you should probably replace the air filter every two weeks, year around.

Bottom Line

This is very important: you should always be removing a relatively clean filter element. If it's too dirty, you're not changing it often enough—even if you're following our schedule. Do not allow that to happen. One more thing: some filters come with a message that says "Change every 90 days." Don't believe it! Change your filter every 30 days, or according to our notification schedule.

Dirty Filter? How Do You Know?

Hold the filter up to the light. Compare what you see, with what you see through a new filter element.

The Scary Part

If your system gets stopped up, just call your AC specialist. His men will clean things up, but it could cost you hundreds of dollars. Is that not incentive enough for you to follow your filter change schedule?

Where to Buy Good Filters

I don't usually recommend one supplier over another, but I'm doing this as a public service. In my opinion, the very best place to buy air filters is Johnson Supply on S. College in Bryan just North of Villa Maria, and just North of the municipal golf course. (Their phone number is 979 775 5554.) The filter quality is high, and the price is reasonable. You can buy any of the filters I have described, but 1" filters come in cases of 12—that's the only way they sell them.


If you'll do a good job at filtration, you won't have as many condensate drain problems, and I don't know anyone who likes water through his ceiling. This is truly kool information that will keep you out of deep water.

Koolest Regards,

Dr. Kool signature

Dr. Kool

p.s. For a complete story on drains, read Dr. Kool's article entitled, Condensate Drains.

p.p.s. If you're not yet registered, by all means do it now—it's easy, and it's free!

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