On Tuesday, September 5, 2017 at 10:19:28 AM UTC-4, wrote:
On Tuesday, September 5, 2017 at 8:20:04 AM UTC-4, TimR wrote:
The purpose of the filter is to protect your coils or heat exchanger, not to clean the air for humans.

It seems reasonable to me that a dirty filter will catch more dust than a clean filter and be better for your coils, up until the point it impedes air flow.


yeah i agree,

and if you keep a thermometer in the duct to monitor the air temperature, if the air flow is significantly impeded, the air temperate will rise in the heating season or drop in the cooling season.

If the duct air temp is normal , the air flow is normal.

m

The air flow may be normal, but the blower could be using more energy
to run. Many newer furnaces have ECM motors, where the motor is
programmed to maintain a constant air flow. How exactly they do that,
IDK. How much of a factor that is in the overall energy usage, IDK,
but if the blower is working harder it will use additional energy.