When it comes to home HVAC units, most can accommodate a filter with a MERV 13 or lower. A 1 MERV 13 pleated filter has a pressure drop of about 0.27, while a 1 MERV 8 has a pressure drop of about 0.14. The pressure drop of a fiberglass filter is approximately 0.1 inches of water. Inches of water are a measure of the pressure differential, which may sound contradictory when talking about air, but can be read more about here.Cheap filters are thin, flat, and usually green or blue, usually costing less than a dollar.
Technicians often wrongly recommend them due to their extremely low pressure drop. However, what they don't tell you is that replacement filters for existing filter channels in existing air conditioning units will normally have a rated speed of approximately 450 to 550 FPM, as part of the original equipment design relative to the maximum surface velocity of the adjacent coil (water retention).Oversized filters will measure the lowest pressure drops as their rated speed decreases. When the rated speed is closer to the median of 500 FPM, the filter material and fold designs will serve to balance pressure drops with the MERV. The load-bearing qualities of the filter can also affect its lifespan. In any case, if the filter slot located in the oven is too small for anything other than a cheap fiberglass filter, it should be removed and placed back in the grille.
The fan must then overcome the added resistance of the filter. In the case of large, deep filters, this can take a long time, and they will look absolutely disgusting long before the pressure drop indicates it's time to change them. In addition, if the Aprilaire filter chamber is aligned with the return duct, there is dirt in the return ducts before the filter and they need to be cleaned periodically. Even 1-inch pleated filters with the lowest MERV have more than twice the pressure loss of a fiberglass filter, making it an easy choice. Just because a filter fits a system doesn't mean it's the best for it. If return ducts are fully channeled, it is possible to replace return grilles with filter grilles and eliminate the filter from the oven.
This way, air travels along the path of least resistance and, in case of a leak between the filter and equipment, it will pass through the filter grid. If you have fully channeled returns and it's easier and less expensive to convert return grids to filter grids and lose the filter in the furnace, use a premium fiberglass filter such as Glasfloss “PTA” for excellent equipment protection while allowing maximum airflow without wasting energy or damaging your oven. One more variable to consider is that four-inch filters have five times more surface area than one-inch filters and can therefore hold more dirt before clogging up your motor. Depending on your type of filter being used, you may need to make a small hole in it with a sharpener or screwdriver to thermostat. Finally, keep in mind that because some systems have two filters, having one with high MERV could be doubly bad. Understanding how average filter pressure drops work is essential for ensuring your HVAC system runs efficiently and effectively. Knowing what type of filter you need for your system and how often you should replace it can help you save money on energy costs while keeping your home comfortable.
