I have pleated air filters for my furnace that have a wire meshing on one side. Which way does the filter go in the furnace with regards to airflow direction. With the wire side opposite of airflow or on the same side as the direction of airflow?
Also, for replacement, what Merv value should I use, is it best to find the highest value or is some lower value actually better?
Why Manufacturers Use Wire Mesh
Many pleated air filters have an aluminum wire mesh on one side of the filter media. This wire mesh is used to improve the filters ability to stand up to the forces exerted on it as air passes through.
Common Characteristics of these Filters
Pleated air filters with wire mesh on one side usually have two characteristics in common:
- They have lower MERV ratings of about 6 to 8 which means they are less efficient than filters with higher ratings and remove less dust.
- The filter material used in these filters is usually cotton or some other material that is not sturdy enough to withstand the stresses encountered in a heating or air conditioning system.
The longer the filter is in use the dirtier it becomes and as it becomes dirtier the forces exerted on it become greater. If there were no wire mesh to help the filter maintain it’s shape it would probably collapse and be sucked out of the filter rack.
Which Way To Install Filters With Wire Mesh
The filter should be installed so that the wire mesh side is toward the fan. This prevents the filter from being sucked into the duct system and causing problems.
These Pleated Filters Do Have Benefits
One of the benefits of these filters is that they have less impact on air flow than filters with higher MERV ratings. This can be very important for systems that have low air flow which is usually the result of undersized duct work.
An Undersized Duct System Can Cause Problems
An undersized duct system can cause efficiency problems and evaporator coil ice ups because air flow is below design parameters. This is where filters with a lower MERV rating shines because they have less impact on air flow than filters with higher ratings.
Don has been working in the HVAC industry for more than 25 years and shares his experience and knowledge on this site. You can also follow him on: