Cast iron radiators capacity: steam to hot water conversion

Old 08-12-04, 04:11 PM
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Question Cast iron radiators capacity: steam to hot water conversion

I am converting a steam system to hot water and I want to calculate the approximate differential between the two systems given that hot water temperature is obviously lower than steam.
The main problem come from the difficulty to find the BTU capacity of a hot water radiator.
An example: I have a 6" x 36" x 38" radiator. It has five tubes in each of it's 14 sections. The Architectural Graphic Standard is telling me that such a radiator will give 5 square feet per section wich makes for a huge 70 square feet. I've never seen such a big radiator in any large appartment room largely exceeding 70 square feet.
This radiator alone has been confortably heating my 1400 square feet loft with 12 feet ceiling for 6 winters at minus 30 temperatures. I therefore assume that this capacity is what is called "empirical feet" and is different from a real life square foot????
It is obviously not the 30 degree difference between hot water and steam! Not to that extent.

My questions:

1-What is the BTU capacity of such a radiator?
2-How many cubic feet can it heat confortably?
3-Is there a rule of thumb for conversion between steam and hot water?

Old 08-13-04, 07:17 PM
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There is a relationship between sq. ft. of radiation and btus. I am not in my office now but I will get that info for you and post back later. The sq. footage is not meant to indicate the size of the area it will heat. The construction values of the area to be heated greatly influence the requirement for radiators. Hopefully this will be the hardest part of the conversion process. You may run into more than you anticipated.


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