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#1
07-21-10, 04:14 PM
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Join Date: Oct 2009
Location: Connecticut
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I Figured out the BTU's of my cast iron Rads at 180deg water temp but does anyone have a chart for the multipliers for lower water temps?

#2
07-21-10, 05:36 PM
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How did you figure the Btus for 180 deg?

#3
07-21-10, 05:55 PM
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#4
07-21-10, 06:01 PM
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Join Date: Oct 2009
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Originally Posted by Mike Speed 30
How did you figure the Btus for 180 deg?

Thanks TO.

#5
07-21-10, 06:22 PM
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Join Date: Mar 2006
Location: USA
Posts: 197

According to this from Comfort Calc/Burnham
at 180F the unit puts out 590 BTUH per linear foot. Subtracting the 15% factor, it's actually 513. The baseray is about 9" tall, so a linear foot is about .75sf, so the total output is 684 per sf.

However, according to this from Comfort Calc/Burnham
a cast iron radiator puts out 170BTUH per sf at 180F.

Am I missing something here? Why the huge difference? Or am I using one of the charts wrong?

#6
07-23-10, 06:58 PM
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The 9A baseboard is 3.4 sq ft per lineal ft. The rads are anywhere between 1 and 3 sq ft per section on tube types and even more on column type. It depends on the type of radiator. The chart you are referring to is once you calculate the sq ft from the type of radiation it is btu's per sq ft of radiator. I don't know where you got the figure of 0.75 sq ft per lineal ft. The 9A chart shows 3.4 sq ft per lineal ft.
I am not sure what the 15% factor is you are deducting.

#7
07-23-10, 10:15 PM
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Join Date: Mar 2006
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Originally Posted by rbeck
The 9A baseboard is 3.4 sq ft per lineal ft. The rads are anywhere between 1 and 3 sq ft per section on tube types and even more on column type. It depends on the type of radiator. The chart you are referring to is once you calculate the sq ft from the type of radiation it is btu's per sq ft of radiator. I don't know where you got the figure of 0.75 sq ft per lineal ft. The 9A chart shows 3.4 sq ft per lineal ft.
I am not sure what the 15% factor is you are deducting.
So the square foot area refers to the total surface area of the radiator (fins and all)? I thought it was the physical size of the radiator - if the radiator is 2 feet tall and 3 feet wide, it's 6 square feet. Hence the .75sf per linear foot for the Baseray - a linear foot is .75' (9") tall, by 1' wide, so .75 sq ft.

The 15% factor is the extra heating factor that IBR allowed baseboard manufacturers to add to their heat ratings. The thought was that because they are lower to the ground than conventional radiators, they are more effective. According to Sigenthaler, this factor has no basis in reality, and if the manufacturer data includes it (as the Baseray data does), it should be taken out when doing calculations.

#8
07-24-10, 11:22 AM
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Location: United States
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Leave it in. The idea of cast iron being about 70% radiant accounts for less air currents which reduces the heat loss. I do not and never have reduced the btu output.
The square ft is the actual sq ft of iron not the physical dimension.