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On some of our windows, we are using a single sheet of eighth inch thick clear Acrylic plastic sheet. The sheet attaches to the window frame via spots of Velcro on the frame. These are very easy to do, not too expensive, and probably add at least R1 of thermal resistance. Payback is excellent -- see below.
In the summer, we will take the Acrylic panels down and store them. Be careful not to block a window that
is required as an emergency exit, and don't use these Acrylic windows where
there are big time heat sources nearby (e.g. wood stoves). |
Here are some pictures:
This is the Acrylic panel in the process of being installed. I did a sloppy job on the Velcro. For the next set I'll use the little round spots of Velcro, and get them in a color that matches the windows frame. I'll also use panes that cover the entire window, rather than the two panes I used on this one.
With Acrylic panel installed. The slight fuzzy look is due to the insect screen on the window. The Acrylic panels themselves are very clear -- you can't really see them at all.
Economics:
If you live in a 7000 heating deg-day climate (mid to north US), and you have single glazed windows now, then for an example 3ft by 4ft window, you might save:
Window area = (3ft)(4ft) = 12 sqft
R value for single glazed windows = 1
R value with Acrylic pane added = 2
Heat Loss single glazed = (7000 deg-days)(24hr/day)(12 sqft)/ (R1) = 2,016,000 BTU per season
Heat Loss with Acrylic pane = (7000)(24)(12)/(R2) = 1,008,000 per season
Cost saving if you use propane in an 70% efficient furnace is:
Gallons saved = (2,016,000-1,008,000BTU)/((90,000BTU/gal)(0.7efic)) = 16 gal/yr saving
Around here, that's worth about $32 per year.
The Acrylic costs about $2 per square foot here, so this 12 sqft window would cost about $24 to do.
So, the payback for single glazed windows is less than one heating season!!
For double glazed windows, the saving is about $11 per year, so the payoff would be about 2 seasons.
Still a 50% return, inflation protected, tax free investment -- try and get that on the stock market :-)
And, it may qualify for a tax credit -- take a look here and see: Rebates
My state (Montana) pays 100% of the cost under the current tax credit for energy improvements program.
Gary
12/5/05