What I'm Seeing Now


With Air Filters The Air Flow Arrow Should Point Toward The Unit

With air filters the air flow arrow should point toward the unit.

While I have never kept track statistically, I bet that more than half the time the HVAC filter air flow arrow is pointing in the wrong direction.

Twice in two days I have seen this.

The arrow is pointing away from the unit.

The air flow arrow is there for a reason.

One side of the filter is made differently from the other.

The filtration mesh is one product and there is a thin, wiry metal, or cardboard structure on the other.

The purpose of the extra structure on one side is to provide additional strength so the mesh material is not drawn into the unit over time.

As the filter clogs and becomes more resistant to air flow, the air pressure will push harder and harder onto it.  At the same time the mesh will become weaker.

In this house a day later I found this.   The larger photo has been cropped to show that on this furnace an air flow arrow was drawn onto the metal return duct above the filter slot, and still the arrow is facing the wrong direction!

One more thing to mention would be regarding the filter slot itself.

The filter slot should be covered!

Air should be drawn THROUGH the filter and NOT AROUND it.

When the slot is vertical and on the side of the return duct, as shown in the photo, the easiest way is to cover it with aluminum tape.

Sometimes the installer will fashion a piece of bent metal or a metal door to cover the slot, which could itself be further sealed with tape.

But still, it is very important that the air is filtered completely.

Which filter should you use - the really cheap one or the expensive, high-filtration one?  You can read about that debate on a previous blog I posted six years ago.  Click here.

My recommendation:  don't discount the small stuff!  Little things like air flow arrows and gaps around the filter make a big difference over time.  You want your system to be clean!  You want your system to last a longer time!  And pay attention to how dirty they get!  During months of high use the air filter should be cleaned or replaced every month!  That might be 8, 9 or 10 filters a year.  Maintenance is maintenance.  And your system will appreciate your diligence and regularity in filter replacement.



Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


Comment balloon 9 commentsJay Markanich • December 15 2016 12:01PM


Jay,  important information especially this time of year with the way the heating systems are working!

Posted by Ginny Gorman, Homes for Sale in Southern RI and beyond (RI Real Estate Services ~ 401-529-7849~ RI Waterfront Real Estate) about 4 years ago

Ginny - where you are that is true!  In some areas the AC is running far more than the heat.  So the advice in this post works there as well.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 4 years ago

Good morning Jay. Too many take filter replacement too lightly! Not a good thing! Enjoy your day with the arrow in the right direction!

Posted by Wayne Martin, Real Estate Broker - Retired (Wayne M Martin) about 4 years ago

Just slap it in there and get on with the day, right Wayne?

You nailed it.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 4 years ago

Great information, Jay. Amazing isn't it how often all you need to do is read the instructions!

Posted by Nina Hollander, Your Charlotte/Ballantyne/Waxhaw/Fort Mill Realtor (Coldwell Banker Realty) about 4 years ago

Good morning Jay. In my former house I used these and never knew that. I simply replaced it as it was.

Posted by Sheila Anderson, The Real Estate Whisperer Who Listens 732-715-1133 (Referral Group Incorporated) about 4 years ago

When they are paying to have their evaporator coils cleaned maybe it will register... lol

Posted by Fred Hernden, CMI, Albuquerque area Master Inspector (Superior Home Inspections - Greater Albuquerque Area) about 4 years ago

Were happy to find them replaced regularly let alone installed in the proper direction. Rocket science it is not.

Posted by Kevin J. May, Serving the Treasure & Paradise Coasts of Florida (Florida Supreme Realty) about 4 years ago

Nina - and you don't even have to "read" an arrow!

Sheila - let's hope it was done right originally!

Fred - in education that is called a connection.  Not everyone is a connection type.

Kevin - it is air and motion dynamics science.  Rockets might fit into that somewhere, but an arrow is pretty simple nonetheless.

Say, isn't a rocket kind of like an arrow?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 4 years ago

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