Casement vs. double-hung windows: Cost vs. air leakage
I’m looking at a whole home replacement window project. I’m going to use Provia vinyl windows. I keep reading that if energy efficiency is a main concern then hung windows are not an option. “Casements or tilt and turn must be used because they have the best air leaking ratings.” I’m also seeing that over time hung window air leakage will degrade. All of that being said, the air leakage ratings on the double hung windows seem fantastic to me. U factor (.19) and SHGC (.27) are identical. (The house isn’t oriented to take advantage of south facing windows so high SHGC is not desired.)
Test Specification – ASTM E 283
Double Hung
Air Leakage – .05 cfm/ft2 @ 25 mph
Casement
Air Leakage – .02 cfm/ft2 @ 25 mph
1. This seems like a tiny difference. Would anyone expect a perceptible difference standing by the window or on energy usage?
2. Is the degradation of the double hung air leakage a considerable factor over time?
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Replies
You could do the math on the energy cost difference (but I wouldn't sweat it.)
A high SHGC makes a measurable difference on heating energy use even on north facing windows, but can increase cooling costs on unshaded east or west facing windows.
Thanks Dana. The long sides of the house face East and West so I guess there's not a lot of opportunity to take advantage of solar hear energy. The North and South sides of the building have minimal windows.
Hi Sean -
I have never seen double-hung windows with air leakage that low. I checked the NFRC Certified Product Directory (http://search.nfrc.org/search/searchdefault.aspx) for Novia double-hung and under air leakage it simply has < (or equal to) 0.3 cfm/sf, what is required in the IRC 2015 code.
Sure sounds good, but hard to believe!