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What is the typical u-value for a tubular skylight, such as the “solatube”? I’m doing some energy calculations and would like to do better than guess. None of the tubular skylight companies publish u-value information on the internet, and won’t respond to my emails in a timely fashion. If I WERE to guess, I would guess about 0.2.
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As a SunTunnel dealer, I may be able to help you out. It's early morning so I don't have access to California, where all the answer grapes are located.
SunTunnel comes in 14" and 22" sizes and the data I have on the dual diffuser 14" based on 1996 testing is R= 3.06 hr./sf.ft/deg.F/Btu which yields a U of 0.327 .
This is the loss across the diffuser on the ceiling. Naturally , you can insulate the tube itself by wrapping it with batts, so that is not the issue. I would say that the 22" model would yield very similar results. I don't have data on the single diffuser/ gasket.
Generally, we install double diffusers in wet areas like bathrooms , indoor swimming pools, and the like to prevent condensation. In most installations we install the single diffuser. See SunTunnel at http://www.SunTunnel.com
*contacted an assoc. and he tells me despite trying to get adequate testing done, no one or not many, will give accurate info on values for it. the nfrc has no test methods. here's another one to contact, and i talked to them today so maybe they're expecting your call....1-800-sun star.or sunstar.com. best of luck to ya.