I've had three different companies service my AC and all of them (including the last one that installed my new system with a warranty) said the cheap fiberglass filters were what they recommended. Just change them often. I have two filters I replace every month and it only costs me ~10 dollars/ month.

When we built the house, I had a discussion with the HVAC contractor about this subject. I asked what he used in his house. He said MERV 8 filters and he designed systems with them in mind to be be used. He also said those systems with a single return or single filter system run the risk of too much restriction being put on the air handlers with too high a MERV rating.

Our system is a 3 ton unit and we have 4 returns, each with it's own filter. We check them monthly and generally end up replacing them about every 3-4 months.

quote:

Originally posted by 12GA:
Monthly? I change mine twice per year. Damn things are expensive.

Size of filter will have a lot to do with it too. My old furnace has 1 inch thick filters and the new one has 5 inch thick filters. The thin filters obviously need to be changed more often. I checked mine the other day as it was replaced 6 months ago and it is barely dirty.

I use 8 merv 20X25X5 that I buy at Menards for $20 but may try 11 merv next time, since we have pets, but personally would not go higher than that due to possibly excess restrictive flow and don't see the need to have that level of filtering in our home.



A chart for different merv ratings. Again the higher the merv number, the more restrictive the airflow. My understanding is that a furnace with variable speed fan motors can automatically adjust for various filters if need be as long as filters are within recommended range of furnace.

Another time when I realize I may be doing more harm than good with the equivalent of a MERV 12 filter. I need to dial those back.....

My furnace came with a Merv 13 filter when it was installed less than two years ago so that’s what I’ve been using when I change it just before heating season and before cooling season.

quote:

1" electrostatic filters pretty much kill HVAC equipment and efficiencies.

Excam_Man, can you expand on this a little bit?
The local big box store sell Filtrete 1" filters that are electrostatic or non-electrostatic.

I use the HD cheap blue ones. My upstairs air handler just failed after 17 years.
It was corroded to the point of no repair but the coils were clean, no build up. They had never been cleaned in 17 years.

When I had my new HVAC installed about 5 years ago the tech told me to buy the el cheapo ones and just spray them lightly with the wife's hair spray before you install them. He said it makes them a little tackier and picks up the smaller particles better. He said he cheaper ones have a better air flow and the unit doesn't have to work as hard. He said to change them about every other month.

quote:

Originally posted by grumpy1:

quote:

Originally posted by 12GA:
Monthly? I change mine twice per year. Damn things are expensive.

Size of filter will have a lot to do with it too. My old furnace has 1 inch thick filters and the new one has 5 inch thick filters. The thin filters obviously need to be changed more often. I checked mine the other day as it was replaced 6 months ago and it is barely dirty

Height of filter also has a lot to do with how quickly they get dirty. This is the first home that I've owned with 12' and 14' ceilings, and the filters need changing a lot less frequently than 8' or 10' ceilings.

All of my filters are in the ceiling returns, and none of them are on the furnace itself. Big difference from the filter on the side of my old furnace in Anchorage where all of the cold air returns were floor level.

quote:

Originally posted by Patrick-SP2022:

quote:

1" electrostatic filters pretty much kill HVAC equipment and efficiencies.

Excam_Man, can you expand on this a little bit?
The local big box store sell Filtrete 1" filters that are electrostatic or non-electrostatic.

First, is most common size filter grills are not properly sized and the electrostatic doesn't provide enough surface area to not be very restrictive.

Second, is with any washable filter. Most of the time they are not cleaned properly and end up being plugged with debris.

Proper airflow is the most important factor in reducing equipment damage/failures and increasing equipment longevity.
Electrostatic filters have woven plastic threads, placed very close to each other, greatly reducing airflow.
When you reduce/restrict airflow this much you have equipment operating above the design temp. Leading to part failures (due to the increase in heat) and stressing the heat exchangers until one day they fail/crack.

quote:

Originally posted by 220-9er:
The better ones filter out smaller particles and miscellaneous other stuff. Shop them by MERV rating.
Decide how small you want to filter out then buy online in case quantity. You'll save a lot that way.

You have to be careful when going up in Merv rating on older installs. Many of the filter sizes were/are on the small side for the tonnage of the unit on older installs and going up in Merv rating can restrict them too much. There is a formula of how many square inches of filter per ton of Ac. It's generally about 1 sq foot (12"x12") of filter size per ton of AC.

This message has been edited. Last edited by: jimmy123x,