Summer Energy Conservation

I am a producer/member of the Oklahoma Food Coop.  It is a wonderful, on-line farmers market and so much more.  It is a group of people – farmers, ranchers, bakers, horticulturists, even jewelers and people like me who bake dog treats – all dedicated to the sustainable lifestyle.  Our president is Robert Waldrop, an overflowing fount of knowledge in all things sustainable.  He has modified his urban house in a historic neighborhood to be more energy efficient than you can imagine.  He has also converted his front lawn to a vegetable/fruit garden.  He is one of the founding members of our local sustainability network and has several websites that address energy and the sustainable lifestyle (   Every week or so he sends emails to the Co-op membership with information and ideas, recipes, etc.  I thought today’s message was especially worth sharing.  His suggestions are something all homeowners can do.  Pay special attention to the end where Bob shares a formula for determining home heat loss or gain.  Enjoy!

“In the summer, shade is our friend.  Yesterday afternoon when the temp outside peaked at 99.9 degrees, I checked the thermometer tucked into the deep shade of the mulberry trees on the west side of my house.  It read 88 degrees.  That’s nearly 12 degrees difference.  Hoorah for vegetation!

If your house isn’t nicely shaded in the summer, now’s the time to plan for the fall planting of trees and shrubs.  (Plant mulberries.  They grow fast and yield the earliest fruit.  Mulberry jam and cobbler are your friends, too, or they want to be anyway.)

Pay special attention to windows.  Even if you have the best double pane, argon filled, low-E coated windows, they still only amount to about R-4 in insulating value (divide the U-value into 1 to get a rough approximation of the R-value.)

Not counting our sun porch, I have 291 square feet of windows.  If those windows were unshaded, we would be pulling in nearly 4000 BTUs per hour of heat into my house from the hot afternoon outside – JUST from the windows!  Shading knocks a thousand BTUs/hour off the heat gain.  Shading plus R-20 insulated shutters for the window brings our heat gain down to 1700 BTUs/hour.  The heat gain for our R-33 insulated walls is about 1000 BTUs/hour, and about the same from our well-ventilated attic.

So even though windows are a much smaller area than the square footage of walls and ceilings, as much heat gets in through them in the summer (and gets OUT in the winter) as the walls or the ceiling.


It’s important that windows be actually shaded.  You still get heat coming through them, but you get less heat if they are shaded from the outside.

One value-priced window treatment that we used until our vegetation got sufficiently shady is to duct tape 2 or 3 auto sunshades together and hang them on the outside of the window.

While it takes a few years to grow a tree, climbing vines like morning glories can cover a window quickly.  To make an easy trellis put eye hooks in the eaves, thread string through them, loop the string through a piece of lumber or pipe anchored to the ground below them; grow the morning glories up the strings (or other fast growing vines with lots of leaves.)

To calculate heat loss or gain, use this formula:

Summer heat gain from the outside to the inside: subtract the interior temperature from the exterior temperature; divide this by the R-value of the ceiling, wall or window; multiply the resulting number by the square feet of the ceiling, wall or window.

You can use this same formula to calculate heat loss in the winter, just reverse the outside/inside temps so you are subtracting the outside temp from the inside temp.

You need a separate calculation for your windows, your walls, and your ceiling in a spreadsheet and substitute different R-values to determine how adding insulation to walls or ceilings, shade to the outside and/or insulated shutters for your windows will impact the movement of heat to the interior in the summer or the exterior in the winter.  Remember, heat always moves toward cold.”

So, there you have it.  Bob’s suggestions for shading your house, and a formula for determining your heat gain/loss.  Very helpful information when trying to lower cooling/heating expenses in the midst of ever-rising fuel costs. 

Please leave a comment and let me know if you found this information to be of help.

Keep it simple,


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