My filter is at the air-handler end of the return ducts, but most, I believe, are at the living-space end. If I were looking for filters, I'd go to the air handler to see where the return ducts originated.
That explains why you found a filter in the ceiling.
AFAIK, the air handler is always on the return side of the evaporator.
Your return duct must run from the air handler to the ceiling filter you found. If there are any forks, each duct leads to a different filter.
For example, I have floor returns in two rooms. Their ducts combine and go to the air handler. My neighbor has a ceiling return in one room and a return low in the wall in another room. Their ducts combine and go to the air handler.
All the ones I've seen here in NJ are like yours, at the air handler. That includes systems from the 50s through ones in new construction today. One reason, would be there are multiple returns in a house that would each need a filter, while at the air handler/furnace you only need one. Also a lot of systems are going in with electrostatic.
The OP found a filter in the ceiling. That's why I assumed any other filters would be accessible from living spaces, like my neighbor's.
I've looked closely at hers because she asks me to change filters. The only other filter I remember is in mine. My house was heated by coal grates for decades. Then oil stoves were added. Then a furnace took over. Then an evaporator was put in the duct. I figured hers was more likely to be typical, but with my lack of experience, it was a guess.
I was thinking of going to an electrostatic filter. Lately I read that an HVAC filter doesn't make much difference in air quality because dust spends most of its time on a surface like the floor, waiting to be disturbed if you don't get it first with a vacuum.
The purpose of the HVAC filter is to protect the air handler from dust. You need to keep the coils and fins clean or they don't transfer heat properly.
It has nothing to do with air quality or protection of people. You can get that kind of filter, but it is not standard.
Yes, if by HVAC filter you mean only the minimal filter that's included with the airhandler. But all kinds of filters are offered by the manufacturers and installed as part of the system. IDK any install I've seen around here that just use the 1" minimal one that's in the air handler.
I guess that depends on your definition of standard. On new homes going up here, electrostatic is widely used now.
You don't typically put more filters, you just put one good one of whatever type you want.
The air handlers I've seen on typical furnaces have been capable of handling 5" media type filters, electrostatic (which have little pressure drop). They are designed so they don't cause too much pressure drop. I have a 5" one here on my 3 year old furnace, nothing special about the blower. They are thick, but pleated with a lot of surface area.
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