88,000 BTU Modulating Gas Furnace 97% AFUE vs 66,000 BTU Low NOx Modulating Gas Furnace 98%

Buy the 88,000 BTU furnace if you are heating a larger home or a colder climate; its extra capacity and wider cabinet move more air. Buy the 66,000 BTU Low NOx unit if you have a smaller or well-insulated house, or live in an area with strict NOx rules. Both are modulating, variable-speed ECM furnaces with 97–98% AFUE and non-communicating controls, so comfort and efficiency are close. The 66,000 unit is the more efficient and cleaner-burning of the two; the 88,000 unit is the more capable.

• Choose the 88,000 BTU furnace if your home is large or leaky, or winters are severe, and you need the higher airflow and heat output.
• Choose the 66,000 BTU Low NOx furnace if your home is smaller or tight, or your local air-quality rules require a low-NOx appliance.