homeassistant

how do you typically notice the filter needs to be changed now? does it:

• draw more power than usual? wattage sensor
• give some alert like a “change filter” light? esp32
• need changing after a certain time/usage amount? power consumption sensor
• need changing every X days? you might just need a calendar alert

of course the mega nerd approach would be to put a particulate sensor in the duct like a PMS7003 that measures PM10 particles like dust, strap on an esp32 and set some alerts using your favourite monitoring tool.

If you have your thermostat in home assistant you only need to track the run time and then have it alert you or trigger a sensor when it's been running for a set number of hours.

Not automated but you can get a radon manometer to identify pressure differentials. Install on both sides of the filter. Identify where pressure is with a new filter, mark it, and see how it changes over time and determine when to replace it.

A modern sensor would be a mass airflow sensor, but a sail switch that you can adjust the amount of surface area that it hits so it alerts if the amount of air isn't high enough it doesn't activate when the furnace is running.