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# cast iron radiator out-put

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Member Posts: 12
MULTIPLY # of sections by square ft per section (5 square ft is a conservative#) and multiply that by water temp
ie-20 sections x5x180=18,000 btuh @ 180 water temp-the burnham htg helper has this in it

## Comments

• Member Posts: 18
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cast iron radiator out-put

Can any-one direct me to a resource or give me a rule of thumb for calculating out-put of cast-iron radiators at various water temps?
• Member Posts: 51
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If you can post a picture of your radiators, with height and width, I have sheets which will identify your type and can give you an accurate amount.
• Member Posts: 6,928
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Average* radiator temperature - room air temperature * multiplier** = BTUs per hour

*If you're working from supply temperature it's generally safe to assume the average radiator temperature is 10F less (e.g. a 20F delta-t [change in temp])

**Multiplier:

For average radiator temps from 140F - 180F use 1.8

For average radiator temps from 90F - 140F use 1.5

For average radiator temps from 75 - 90F use 2.0

This is a reasonable estimate for the most common forms of standing iron radiators, e.g. 30" - 40" tall and about 8" deep.

For short (say < 20") and deep (at least 12") rads, add 0.25 to the multiplier.

For tall (at least 30") and deep (10" or more) rads, subtract .25 from the multiplier.

For tall (at least 30") and shallow (4" or less) rads add 0.25 to the multipler in the two lower temperature ranges and subtract 0.25 from the highest range.

Due to an enormous range in actual radiator design this is slightly conservative. It's based on research, personal measurement and independent verification from a source I pledged never to divulge.
• Member Posts: 174
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Just out of curiosity.....

If you immersed a ci rad with 180 degree water moving through it into a tank of 130-degree water, would it transfer more heat into the water than it would into the air?

All other considerations aside, in other words, would a ci rad make a good heat exchanger?
• Member Posts: 2,398
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Yes

Water is a better conductor and would transfer more heat per degree F. difference when immersed in water than in air.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad
• Member Posts: 6,928
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Most certainly! It would transfer FAR more energy to water than to air.
• Member Posts: 18
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Thanx

for the replys. Mike T, the multipliers you gave, are they per section of radiator, or /sq ft of surface area, or am I not understanding the formula?
• Member Posts: 6,928
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Per square foot of EDR (equivalence of direct radiation).
• Member Posts: 18
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ok

thanx
This discussion has been closed.