Older boiler ratings: heating area sq ft?

Gilmorrie

Older heating boilers' nameplate ratings often included heating surface area, in sq ft. For example, my 70-year-old firetube, Kewanee hot-water boiler has 41 sq ft. This is the total surface area of the firetubes. A larger heating surface area should help wring more heat out of the flue-gas and help improve efficiency - so, heating area was something to consider when comparing boilers. Nowadays, the heating surface area is seldom if ever mentioned or listed in specs. Why?

bburd

Manufacturers are now required to rate the efficiency of their boilers using standardized testing methods. The heat exchanger surface area is therefore no longer relevant to the heating system designer or owner. 

EBEBRATT-Ed

Heating surface was an old way of trying to compare boilers and is a holdover from back in the coal burning days. It was never all that accurate. Sometimes still used when discussing larger scotch marine boilers

pecmsg

Gilmorrie said:

Older heating boilers' nameplate ratings often included heating surface area, in sq ft. For example, my 70-year-old firetube, Kewanee hot-water boiler has 41 sq ft. This is the total surface area of the firetubes. A larger heating surface area should help wring more heat out of the flue-gas and help improve efficiency - so, heating area was something to consider when comparing boilers. Nowadays, the heating surface area is seldom if ever mentioned or listed in specs. Why?

I believe that rating was Sq Ft of Radiation!

ethicalpaul

pecmsg said:

Gilmorrie said:

Older heating boilers' nameplate ratings often included heating surface area, in sq ft. For example, my 70-year-old firetube, Kewanee hot-water boiler has 41 sq ft. This is the total surface area of the firetubes. A larger heating surface area should help wring more heat out of the flue-gas and help improve efficiency - so, heating area was something to consider when comparing boilers. Nowadays, the heating surface area is seldom if ever mentioned or listed in specs. Why?

I believe that rating was Sq Ft of Radiation!

Not if it was 41 feet 😅

EBEBRATT-Ed

Older boilers were rated in sq feet of heating surface. Some were rated in sq feet of grate area. Scotch marine boilers are rated at 5 square feet of heating surface /boiler horsepower

Gilmorrie

Thanks for your comments, very helpful.

Correct - the 41 sq ft applies to the heat transfer area between the flue side and the water side of the boiler - not room radiators. That 41sq ft is on the boiler nameplate. My radiators are very much larger.