Session Info

Ultraclean Condensing Furnace


Residential natural gas furnaces are widely used for space heating in US homes. However, the acidic components in furnace combustion gases, such as SOx, NOx, and formic gases, pose a significant environmental challenge. In particular, the acidic gases combine with water vapor to form an acidic condensate with a pH ~3, which is more acidic than typical acid rain. The acidic condensate leads to corrosion and fouling problems. Furnace manufacturers and utility customers are actively seeking a solution that eliminates acidity in furnace condensate, reduces emissions, and achieves high efficiency and simplified installation.


The Ultraclean Condensing Furnace addresses these challenges. By incorporating compact and cost-effective acidic gas reduction (AGR) components, the technology achieves ultraclean flue gas and neutral condensate. The novel furnace design can remove more than 99.9% of acidic gases and other emissions, including trapping over 95% of SOx, reducing over 95% of NOx, and oxidizing formic acid/CO/HC/CH4 by nearly 100%. This results in the discharge of neutral condensate. The neutral condensate allows for a simpler and less expensive furnace design by utilizing a large low-cost secondary heat exchanger (HX). That enables ultrahigh furnace efficiencies and eliminates the need for an acidic condensate treatment system.


The Ultraclean Condensing Furnace has the potential to revolutionize the residential heating market. With the majority of 118 million homes in the US relying on natural gas furnaces, the technology’s impact on environmental emissions can be substantial. The AGR-enabled furnace achieves ultralow emissions compared to the US EPA furnace standard. Additionally, the absence of CO emissions substantially simplifies ANSI certification for original equipment manufacturers and allows for safer operating conditions. The neutral condensate enables a simpler and more cost-effective furnace design, providing higher efficiencies and eliminating corrosion concerns. The applicability of AGR and clean furnace technologies can extend beyond residential condensing furnaces to other natural gas HVAC devices.


Gao, Zhiming, et al. “Nondestructive neutron imaging diagnosis of acidic gas reduction catalyst after 400-Hour operation in natural gas furnace.” Chemical Engineering Journal 454 (2023): 140099.

Gao, Zhiming, et al. “Ultra-clean condensing gas furnace enabled with acidic gas reduction.” Energy 243 (2022): 123068.

Intellectual Property

“Advanced Adsorption Technology for New High-Efficiency Natural-Gas Furnace at Low Cost,” Invention Ref. No. 201804153


For more information, please contact Andreana Leskovjan (865-341-0433,


Zhiming Gao

Zhiming Gao