Question: I have a whole house electric AC with gas heat in my home, which is approximately 1800 sq ft. There are 2 return air grills with filter in the house and a filter tray at the bottom of my furnace in the return air system.
The sizes are as follows:
Grill #1 is 20×20x1
Grill #2 is 20×24x1
The under furnace tray is 24×24x1
What filter combination should I run? Filter in all 3? And what type. I’m looking for the best airflow (low pressure drop) with the most filtration.
If you are looking for the best combination of air flow and filtration I would recommend a pleated filter with a relatively high MERV rating 10 - 12 and change it monthly. Although filters with higher MERV ratings have more pressure drop than air filters with lower MERV ratings, they will provide the best filtration. Change the filter monthly to prevent the air flow from being effected greatly.
Stacking filters is not a good idea because combined they may cause excessive pressure drop and can be far worse than having one pleated air filter with a high MERV rating. I would remove the filters from the return air grills.
If you are interested in upgrading your system, you can install an electronic air cleaner and install a pleated air filter as a pre-filter. Electronic air cleaners have almost no effect on air flow. Remove the foam pre-filter that comes with the electronic air cleaner and use a pleated filter instead. This combination will provide the best filtration and the least pressure drop.
Question: I have a UV air cleaner in my home. What MERV rating air filter do I need to use? Would it be beneficial to use a MERV 11 filter or would a MERV 8 work? I change my filter every month when it’s running but I will go for 3 months. I have changed the filter at different times and it seemed (by the naked eye) clean. Should I let it go longer or still go on the same maintenance cycles?
A UV air cleaner doesn’t eliminate the need for efficient air conditioner filters. The UV air cleaner will help to kill mold spores, bacteria and viruses but they don’t actually filter the air, they only purify it. You still require an efficient air filter to remove dust particles from the air.
A MERV 8 filter is adequate for most homes unless you want to maintain the best air quality possible. A MERV 11 filter is very efficient and will do a good job.
How often should you change your filter
It is best to follow manufacturer recommendations for filter change frequency. They know their products and can better guide you in this area.
Personally, I think changing furnace filters and air conditioner filters every month is more often than necessary. I usually change filters every 3 months in commercial buildings. If every 3 months is good enough for these applications, where there is more dust, then it should be fine for residential applications.
One thing to consider is that filters used in commercial applications usually aren’t as efficient as the ones used in residential applications so they don’t become dirty as quickly.
If you can tell by looking at your furnace filter or air conditioner filter that it is not getting dirty then it probably doesn’t need to be changed for a while.
Other articles about how often to change air filters
When To Change Your Air Conditioner Filter
Every house is different and there are many factors that determine how often your heating and air conditioning filters should be replaced. If you wait too long operating efficiency begins to decline, as efficiency drops operating costs increase. Changing your air filter more often than necessary is like throwing money away.
