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The original was posted on /r/homeassistant by /u/seriousthrillissues on 2026-04-04 22:54:18+00:00.
Replacing furnace filters based on the calendar is dumb, changing them when they need to be changed is what we want to do.
Since I can't leave well enough alone and I want to wring every drop of data out of this house, I overengineered an HVAC health monitor using ESPHome and Home Assistant in the same spirit as my mimic wall.
Under the hood, we are running an ESP32, three Sensirion differential pressure sensors on an I2C multiplexer, and three Dallas 1-wire temp sensors. And because we like flashy stuff, I built some custom LED bar graphs out of WS2812B rings.
Here is what the rig is actually watching:
- Total External Static Pressure (TESP): Basically monitoring the supply side so I know if too many vents are closed and the blower is choking.
- Filter Pressure Drop: Measuring the exact pressure difference before and after the return filter. No more guessing, I know exactly how clogged things are.
- Coil Pressure Drop: Watching the pressure across the heat exchanger and coils to catch things like frozen coils before they become an expensive problem.
- Delta T: Reading the exact temperature of the air entering the system versus the air leaving it.
I take all those raw numbers and math the holy hell out of them. The ESP32 does LED things and then blasts the whole package over to Home Assistant for logging and alerts.
It is completely unnecessary, totally overbuilt, and it works perfectly.