The Honeywell Home C-Wire Adapter (THP9045A1098) is a handy device designed to power smart thermostats in homes lacking a common wire. It's compatible with most Honeywell Wi-Fi thermostats and RedLINK® 8000 Series models, making it a versatile choice for upgrading older systems.

Installation is straightforward, with easy push terminals and an adhesive mount for quick setup. Users report that it works well with various systems, including forced air, hot water, steam, and heat pumps with electric backup. However, it's not suitable for electric baseboard heat (120-240V).

Many customers found the adapter easy to install and effective in enabling modern thermostat features like fan-only mode. One user successfully paired it with an Amazon Smart Thermostat, though they initially faced a minor hiccup with a blown fuse that was easily resolved.

Some important notes from user experiences: The adapter combines fan and condenser wires to free up a wire for use as the C-wire. If you have an unused wire in your thermostat cable, you might not need this adapter - simply connect that wire to the C-terminal at your furnace.

While most reviews are positive, one user reported receiving a defective unit that didn't supply power to their Alexa thermostat. Always verify compatibility before purchase and check if your system already has an unused C-wire available.

Overall, this adapter gets the job done for most users looking to upgrade to smart thermostats in older homes without existing C-wires.