Mechanical Hub recently posted that the Utah Department of Environmental Quality (DEQ) has issued proposed new Rule R307-230, NOx Emission Limits for Natural Gas-Fired Water Heaters, which specifies the following NOx emission limits: 

The proposed rule applies to the sale or installation of covered water heaters on the following staggered schedule of locations and corresponding implementation dates:

(Original article: http://mechanical-hub.com/utah-proposes-nox-rule-for-water-heaters)