An ESP32 ESPHome device in the furnace room reads a differential-pressure sensor across the filter and watches the furnace control board’s status LED. Home Assistant turns the raw pressure into blower speed, filter loading, and a replace-filter alert. The threshold comes from a real clean-filter-vs-old-filter experiment, not a guessed limit.

A basement dehumidifier whose built-in control restarts the compressor within 30 seconds of finishing a cycle. Two ESPHome boxes replace that with a wide, adjustable deadband and an anti-short-cycle timer, no Home Assistant, no cloud. Ships as three config pairs: a learning-only simple pair, a full pair for a home Wi-Fi network, and a full pair for buildings with no Wi-Fi at all.