As of January 1, 2025, any replacement or installation of a gas-fired heating appliance in a 1 & 2 family (R3) or multifamily (R2) building will require the installation of a carbon monoxide (CO) detection system, in accordance with section R315.2 of the 2021 International Residential Code (IRC) and section 308.1 of the International Existing Building Code (IEBC).
Please see the this attached document for more information.