Old Boiler Nameplate Terminologly

Gilmorrie

In years past, boiler nameplates listed the heat transfer area in sq ft. For example, my 65-year-old Kewanee boiler lists its heat transfer area as 41 sq ft. (As a fire-tube boiler, the heat transfer area comes out to the outside area of the fire tubes.) A "figure of merit" was the Btu/hr/sq ft - the lower the better. What was that all about? Bigger is better, and fuel is cheap?

My boiler has Btu/hr ratings, input and net, for "mechanical" firing and for "hand' firing. I believe that hand firing was for coal and mechanical firing was for either gas or oil. How did those terms come to be used?

My boiler's Btu ratings for mechanical firing are significantly higher than for hand firing. Why?

My boiler's maximum working pressure is 15 psi for steam and 30 psi for water. Why the difference?

The boiler has an ASME "H" stamp.

EBEBRATT-Ed

Most "modern" boilers (scotch marine & steel firebox boilers) are rated at 5 square feet of heating surface/ boiler horsepower=34.5 lb. of water evaporated/hour @ 212 deg= about 33,475 btu/hour. Older boilers(HRTs & Locomotive boilers) were usually rated at 10 square feet/ boiler hp.

Burning coil and wood required a larger combustion area than gas or oil is one explanation

SWEI

Gilmorrie said:

My boiler's maximum working pressure is 15 psi for steam and 30 psi for water. Why the difference?

30 PSI water and 15 PSI steam are considered low pressure boilers, which are allowed (in most jurisdictions) to be installed by a plumber or a heating contractor. Anything with higher pressure or above a certain size (400,000 BTU/hr in many jurisdictions) requires a different type of license (not to mention insurance.)