The DOE rule requires the elimination of “all non-condensing natural gas furnaces,” which could force consumers to spend thousands of dollars to be in compliance.

The rule will effectively ban the sale of non-condensing gas furnaces and, according to the American Gas Association (AGA), will affect 55% of U.S. households.

The final rule from the U.S. Department of Energy, issued recently, requires newly manufactured indoor residential gas furnaces to be at least 95% efficient starting in December 2028, meaning furnaces made after then will have to be condensing models.

The NPF Hydro-furnace, Navien Inc.'s first HVAC product, claims an annual fuel utilization efficiency of 97% and can be outfitted to burn either natural gas or liquid propane.