Just wanted to put out there my thoughts on something to tell me when my furnace filter needs to be changed. I was thinking about a small pressure sensor in the air return right before the furnace. You wouldn’t even really need to know exact values, just be able to measure the change in pressure over time. My thinking here is as the filter clogs up, less air gets through, thus less pressure.
I like to research things for stuff like this, like Pitot Tubes and MEMS pressure sensors, but have no ability to do anything with them.
But in the end like like something with real data, this is the change in airflow, as opposed to just “hey it’s been x months, maybe you should change it?”