The TPB Immersion Gas Fired Series of hot water boilers (20 HP to 125 HP) is well known throughout the industry for its unique SMALL footprint from a compact two-pass firetube design and burner technology. The two pass immersion gas fired 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. The benefits of the technology in the TPB Immersion Gas Fired Firetube Series hot water boilers include: Natural Efficiency Up to 84% efficiency Two-pass design captures additional flue gas heat after heating primary surface Fueled by natural gas, LP gas, or Biogas Full load of hot water within 14 minutes! Compact Design Saves Space Utilizes the same single-pass immersion technology Very compact footprint ( sizes 24 sq. ft. to 42 sq.ft) 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 -Best in the Industry ! Ease of Maintenance Hinged door provides quick access to burners, manifold and heating tubes for easy cleaning and routine maintenance No refractory; thereby, eliminating annual maintenance and replacement costs ! Trimmed with non-proprietary components Simplicity of Design No complex controls which require intensive training Fewer moving parts reduces incidence of failure and required retuning UL packaged Low NOx Emissions Less than 30ppm NOx.