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# CALCULATING BTU OUTPUT OF CAST IRON RADIATORS WITH HOT WATER

Member Posts: 10
TRYING TO FIGURE OUT THE BTU OUTPUT OF MY CAST IRON RADIATORS. THEY ARE CURRENTLY USED WITH STEAM BUT IM GOING TO INSTALL A NEW BOILER AND USE THEM FOR HOT WATER. THEY MEASURE AS FOLLOWS 38" HIGH AND 5 TUBES PER SECTION . THE SYSTEM IS DESIGNED WITH A 180 DEGREE TEMP WHAT IS THE OUTPUT PER SECTION WITH THESE ANY HELP WILL BE GREATLY APPRECIATED

• Member Posts: 552
Sections

How many section of radiator are there.A picture will help.
• The BTU

output for steam rads is 240 sq/ft.
HW in the same rads is another matter that depends on the water-temperature.
This can only be determined by a complete HL calculation.
180 is a pretty high design temp to use, the lower temp you can get away with, the more efficient the boiler you can use.
However, here`s some info from Burnham that should help determine what you have.

Dave
• Member Posts: 1,404
From Burnham's table

Compared to 215°F (0.9 PSI) steam at 240 BTU/SF

@ 180°F: 170 BTU/SF (71%)

@ 170°F: 150 BTU/SF (62%)

@ 160°F: 130 BTU/SF (54%)

@ 140°F: 90 BTU/SF (37%)

@ 120°F: 50 BTU/SF (21%)

For 38" 5 tube slenders assume 5 SF/section at 215°F Steam, so 3.5 SF/section at 180°. 3.1 @ 170°, & 2.7 @ 160°.

Full structure heat loss calc should tell you how low you can go in water temp. w/ the existing radiation.
• nbc

Is that not what I posted in PDF?,, sheesh.

Dave
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