The “BT Series” is well known throughout the industry for its unique single-pass design and immersion” burner technology. The single pass immersion firetube design delivers premixed air and gas through multiple burner nozzles. A corresponding flue tube (“firetube”), completely immersed in liquid, is aligned with the nozzle head inside the combustion chamber. Upon combustion, the nozzles generate a focused, high velocity flame which radiates down the center of each tube. A UL packaged water heater. The benefits of the technology in the SPW Immersion Fired Series water heaters includes: Efficiency Up to 84% efficiency Radiant heat is maximized across the primary heating surface “immersion process technology” Fueled by natural gas, LP gas, biogas or combo gases Large volume Full hot water design in less than 8 minutes – ideal for industry process heating. Low Maintenance Cost and High Longevity Elimination of thermal shock due to balanced heat transfer across primary heating surface; allowing for up to 150° F ΔT Backed by a 20-year non-prorated thermal shock warranty No Refractory Ease of Maintenance Hinged door provides quick access to burners, manifold and heating tubes for easy cleaning and routine maintenance Trimmed with non-proprietary components Full interior access for inspection within 15 minutes No refractory; thereby, eliminates thousands of $ dollars in refractory maintenance and replacement costs Simplicity of Design No complex controls which require intensive training Fewer moving parts reduces incidence of failure and required retuning Low NOx and CO Emissions Less than 30ppm NOx Less than 50ppm CO.