How much R- value do insulating shades/ blinds add to a window?
american green
| Posted in Green Products and Materials on
They are somewhat tight on the top and bottom but have around a half to quarter inch space up the sides. Installers and salesman will tell you they can make hair grow on an apple- should I believe them?
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Replies
Hi Terry - I wrote a blog on this a bit ago: Do Window Shades Save Energy?
The main problem right now with interior shades is a lack of a standardized test to evaluate their thermal performance. My understanding is that the industry is working on this, but take a look at the blog for starters.
As Peter indicates, "somewhat tight" is nearly worthless for winter heat retention, though it might reduce summer heat gain.
Full 4-sided sealing is necessary to gain any significant winter time efficiency, and the Window Quilt is the only product I know of which will meet that standard (other than the Comfort Shade which my neighbor used to produce). Window Quilt claims an R-5 advantage with its multi-layered reflective (lowE) material.
But, as Peter's blog points out, even an effective shade is only as good as the user's ability to operate it properly so as not to lose winter solar gain or daylighting.
And shades of any sort can increase condensation potential on the windows (by cavity air temperatures) and result in rotted sash and sills.
Quality lowE windows with properly designed shading overhangs (or awnings) are the most effective and only truly passive approach to year-round fenestration efficiency.