Yes, you can replace your Kidde FX-HD heat detector with the Kidde KIR-HD Intelligent fixed temperature/Rate-of-rise heat detector. The KIR-HD is designed as a direct replacement for the FX-HD, so you shouldn’t encounter any compatibility issues. However, it’s always a good idea to double-check the specifications and installation instructions to ensure a seamless replacement process. If you have any concerns or questions during the installation, feel free to reach out to our support team for assistance.