Bryan RV Series “Flexible Water Tube” steam and hot water boilers are forced draft gas, oil and dual fuel fired. They are available in eight standard sizes from 3,500,000 to 8,000,000 Btuh. Bryan guarantees the RV Series’ efficiency to be 84% for hot water boilers and 82% -15psi/80% -150psi or better for steam boilers. Bryan’s exclusive “Flexible Water Tube” design eliminates the possibility of damage from so-called “thermal shock.” Tubes are easily individually replaceable without welding or rolling.