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Home Care Library

Forced Air Heating

The Home Wizard app calculates your ideal home care program to avoid problems with your Forced Air Heating, but sometimes trouble can still occur. Here are answers to questions about forced air heating air flow direction.


Dear Wizard,

Can you please tell me how I can determine the air flow direction in my forced hot air system. I know that the filter is installed between the square opening in the duct work and the fan motor but?????which direction does the arrow on the filter go??????


Dear Michael:

There are a couple of ways to verify which direction air is flowing through the air handler for your forced hot air system, because you are correct that air filters are made to go in a certain direction, which is why they have the arrows on them showing which way they should be put in. But like you said, you need to confirm which way the air is flowing to be sure you are putting the filter in the right way. This is especially important if you are moving to a new house where you can't be sure that the previous owner placed the air filters correctly in the right direction.

So, here are a couple of ways to determine air flow through an air handler for a forced air heating system:

1) if you can follow the ductwork on either side of the air handler, check to see if that side goes to a return vent or to an air register. Air comes in from return vents, and then goes through your air handler, then out of an air register. So if you can see where either side of your ductwork goes, it will allow you to determine the direction of air flow.

2) on the other hand, a sure-fire way to determine air flow through your air handler, is to tie a string to your finger that is about 6 inches long. With your filter out, turn your air handler on, and then put your finger with the string on it near the opening to where your filter would have gone. The direction that the string goes is the direction of your air flow through your air handler. One hint: tie the string on to your finger well, otherwise if it comes off, it could get sucked inside.

Hope this helpful.

Forced Air Heating