Do you have rooms in your house that are colder than other rooms in the winter? If you have air conditioning, are those same rooms warmer than other rooms in the summer? It's common for that to happen to rooms farthest from the blower on the furnace or air conditioner. You can buy booster fans that sit on top of or under registers to blow more air into those rooms.

With this project, you can make your own booster fans. The idea is to use commonly available and inexpensive PC case fans to do the work. A small circuit board and microprocessor provide the smarts. When the furnace or air conditioner is blowing warm or cool air into the room, the Ventbot automatically turns the fans on to provide a boost. When the furnace or air conditioner stops blowing, the Ventbot turns the fans off. It should be the case that once you have it built and installed, you can just set it and forget it.

The project uses this custom PCB, an ESP32 microprocessor, off-the-shelf PC case fans, and a 3D printed enclosure. With provided custom firmware for the ESP32, it can operate stand-alone or be easily integrated into a home automation system.

For details build instructions, including many photos, go here: https://www.instructables.com/Ventbot-a-DIY-Home-HVAC-Vent-Booster-Warm-Side-Coo/

If you want to read the "behind the scenes" project log, you can find it here: https://hackaday.io/project/186808-ventbot-warm-side-cool-cool-side-warm