PFTA 4-Pass (Steam)

In 1978, Johnston introduced the first single furnace waterback 4-pass Scotch Marine boiler. Water backed reliability with 4-pass design efficiency? A dream come true. Every Johnston 4-pass maximizes effective heat transfer using a full five square feet of heating surface per BHP, while at the same time eliminating tube sheet stresses and costly maintenance repairs that are common with dry backed designs.