C.R.S. § 25-7-1503

(1) Except as described in subsection (2) of this section and as modified by rules promulgated by the executive director or the commission pursuant to section 25-7-1506 , this part 15 applies to the following new products: (a) Water heaters with a rated heat input capacity of two million BTUs per hour or less; and (b) Fan-type central furnaces that: (I) Require either single-phase or three-phase electric supply; (II) Are used for comfort heating; and (III) Have a rated heat input capacity of less than one hundred seventy-five thousand BTUs per hour, and, in the case of combination heating and cooling units, a cooling rate of less than sixty-five thousand BTUs per hour. (2) This part 15 does not apply to: (a) Products held in inventory in Colorado on the effective date of the applicable standard; (b) Products that were installed in manufactured homes at the time of construction; (c) Products designed expressly for installation and use in recreational vehicles; or (d) Products that do not burn fossil fuels.