He also differentiated between what Manual J calls “opaque panels” and glazing because the R-values of those components were different. Mills factored in the all of the building enclosure area, and that’s where the heat loss and heat gain happen. I don’t do anything with steam heat, but this story is interesting in contrast to the common rule of thumb based on floor area only. Actually, I should say it led to a good approximation of the capacity of steam heat they needed in those buildings. But it worked well enough for those old buildings because Mills figured out the factors (2, 20, and 200) that led to a good approximation of the heating load. Note that it’s not a true load calculation because it doesn’t use actual heat transfer equations. For typical heating conditions in those 19th century buildings, each square foot of EDR provided 240 BTUs of heat to the building. Click the image to read about him on .Īdd those three numbers together, and that gives you the Equivalent Direct Radiation (EDR) in square feet. John Mills developed the 2-20-200 rule for heating loads in 19th century buildings. Divide the total volume of air in the building by 200.
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