Keeping Cool

START HERE to learn about easy, affordable and effective measures you can take to reduce your summer cooling bill, and make your house more comfortable in the process.

I. Overview:

Keeping cool in the hot-weather months inevitably conjures one of two images: a) sitting motionless on a sticky couch for hours on end, sipping a wet glass of lemonade and smelling like a cave man, or b) some sort of air conditioning system running around the clock, and a corresponding electric bill that’s so big it’s delivered on a dolly.

But oh, ye misled homeowner: it need not be this way. Building science principles (why did they not teach this stuff in school?), and dormant common sense dictate a number of measures any homeowner – including you! – can take to increase comfort, decrease wasteful spending, and lead a better, more fulfilling life. As the most efficient means of keeping cool is, well, warding off the heat, this article examines the principles behind summer heat gain, as well as actionable, affordable measures that will reduce it.

II. The Basics:

Your house is constantly absorbing heat. It makes you uncomfortable. You want it to stop. Here’s what you need to know:

Heat gain is divided into four categories: solar heat, internal heat, air leakage and heat transmission.

Solar heat hits the roof and walls, and comes in through the windows, accounting for about 50% of summer heat gain.

Internal heat gains come from lighting, stoves, showers, human bodies, uninsulated hot water pipes, etc… and account for about 20%.

Air leakage – that is, nice cool air leaking out, and outdoor air that’s been getting baked by the sun all day leaking in, which accounts for about 20%.

Heat transmission, the process that occurs when hot outdoor air seeks equilibrium with cool indoor air, and thus moves through the building shell, accounts for about 10%.

If you want to stay cool (and you do), you want all of this heat gain to end. Here’s how to make it happen.

III. Taking it on:

Solar heat:

Since most heat gain is solar, it’s a logical first step to address this first.

A lot of the heat reaching you does so in the form of radiant heat through solar heat gains. Basically, your roof and walls sit there absorbing heat all day like a hot-pocket in a microwave. Because it’s a giant, hot object, it sends that heat every which way, which includes downward into your house. Imagine living in a shack made of steaming hot-pockets. Or having a giant hot-water radiator cranked at full tilt sitting in your living room on a hot summer day. That’s what your house basically becomes – a giant radiator.

Solar heat also enters your home through the windows. While drawing the curtains will keep some of the heat (and all of the light) out, the window itself continues to absorb heat and act as a radiator (like the roof). The more effective way to limit heat gain through the windows is by preventing the sun from hitting the windows in the first place. You can do this with exterior shade screens or planting some trees.

Air leakage:

Air leakage can be addressed the same way it is in the winter, which is with some good old-fashioned elbow grease. A caulking gun wielded skillfully in the attic can take a big bite out of air leakage heat gains. It is true, though, that a lot of major air leaks won’t be immediately visible, which is why it’s a great idea to have a home energy auditor come take a peak. His blower door and infrared camera will find the culprits in no time flat.


Transmission is heat moving through your walls, and the only way to stop it is by beefing up your walls with good insulation – just as important in the cooling season as in the heating season. Heat gain through transmission is only responsible for about 10% of summer heat gain – a lot of smaller, less expensive projects may be equally effective.

Internal heat:

Reducing your internal heat gains barely even requires getting your hands dirty. Getting rid of the incandescent light bulbs (which emit 90% or more of the electricity they consume as heat) is a good first step. Use a microwave instead of the stove whenever you can (more of the heat actually goes into the food, less wasted heat, a cooler house), and maybe cool down those showers a bit (it is summer after all). Oh, and human body heat also contributes to internal heat gain – so have a glass of lemonade or something. Chill out.

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