Window R value in calcs?
If the info in “Windows as good as walls”, etc, is true (and I have no reason to doubt it), what does one use for an R-value when making rough heat loss calcs for a house? If an entire window has an R of 5, say, then it’s effective R value is somewhere between +5 and -5, is it not? I am just using the standard normal Q = UA (delta T), as I don’t know how to calc solar heat gain, and it seems to oversimplify what a good window does to treat it like an R-5 wall section. Is there some grossly approximate rule of thumb to use for said window’s R value in a sub-arctic environment? The above referenced article mentioned some windows gaining about as many btu’s as they lose, but I did not see what percent of those gained btu’s are usable, ie garnered when they are needed, and not just let back out the open window because it is warm outside. Am I looking for another holy grail? The house harboring these windows would be in a fairly high, fairly sunny location; nothing deep in tangled black spruce, and nothing on the top of Shaktah Ridge. Thanks. klingel
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