How To Keep Your House Cool Without AC when 100-degree heatwaves strike, should you close windows or leave them open? How do you keep the upstairs cool naturally? We have answers.
Before you start firing up your energy-burning, power-bill-boosting AC, consider revisiting techniques that our great-greats used to stay cool in summer. Three simple strategies will go a long way to keeping the inside of your house more comfortable.
1. Open Windows Strategically
If you have windows that you can open, do so only when it is cooler outside than in. But don’t just throw them all wide open. While that may seem like the way to get the most air movement, it often isn’t. Take advantage of the fact that hot air rises (think hot-air balloon), and create a natural draft by opening downstairs windows on the shady side of the house, and upstairs windows on the hot side of the house. Increase this natural flow by putting a portable window-mounted fan in the upstairs window. To get the best effect, experiment with how wide you open the windows; usually it takes only a few inches downstairs. If there is any natural breeze, “tune” your windows to work with it: Open downstairs windows on the side of the house the wind is hitting, and upstairs windows on the side of the house away from the wind. As the wind swoops over and around your house, it actually decreases the air pressure on the far side, and that lower pressure will pull hot air out of your home. If you live in an area with lots of pollen or dust, you may want to get window screens with filters in them for the downstairs windows. Once the outside air starts to warm up in the morning, be ready to close your windows up tight. If you are leaving for the day, you will want to shut everything up before you go out.
If you own your home and there are only a few nights a year when the outside air doesn’t get cool enough for sleeping, you can take advantage of cool outdoor temperatures even more effectively by installing a built-in, whole-house exhaust fan. It will exchange all the air in your home in just a few minutes. A less-expensive option is an attic fan designed to just vent heat out of the attic. You buy an attic fan that comes with a small solar panel and runs only when the sun shines (which is pretty much when you need it). They’re easy to install, no wiring involved. You can also use portable fans or ceiling fans to make yourself more comfortable indoors (or even on a porch or patio); the moving air evaporates moisture off your skin and takes some heat with it. Since fans don’t change the temperature of the air-they just cool whoever’s in the breeze-be sure to turn them off when no one is there to enjoy them. While running fans does take electricity, it’s just a fraction of the power an AC unit uses.
2. Reduce And Reflect Sunlight 
Sunshine is wonderful stuff, but it’s your enemy when you want to stay cool. Anything you can do to keep it from shining onto and into your house will help keep you cooler. That includes making your house and roof more reflective-reflective roof paint can make a sizable difference-and, especially, keeping sunlight from shining in through your windows. Why is the last so important? Sunlight is much more than visible light; it also contains ultraviolet (UV) radiation and infrared radiation (heat). Heat doesn’t travel through glass very quickly, but visible light and UV radiation do. And when they hit air molecules, or solid objects like your skin or the floor of your living room, a significant portion of their energy is converted to heat. This  mini greenhouse effect is great when it’s cold outside, but not so good when it’s hot.
Closing drapes and shades can help keep out the visible light and UV rays so they don’t get converted to heat, so close them whenever your windows are closed-especially on windows that get direct or reflected sun. Even covering the windows with a portable screen or a large sheet of cardboard will keep the sun’s rays out quite effectively. Insulated window coverings are even more effective, as they help block the heat portion of the sunshine that comes in through the glass and frame.  If living in a cave bums you out and you have some money to spend, you can cover the insides of windows with special film to help block a portion of visible light and UV rays without totally blocking visibility. Removable film allows you to take it off during the winter when you want the free solar energy. There are also window shades designed to let you see out but still block most of the direct rays. Mesh ones don’t need adjusting; slatted ones may need to be adjusted as the sun moves. Replacing your windows may be an option if you have money to spare (and tax incentives may help offset the cost), especially if they are leaky and old; doing so won’t pay for itself as quickly as using drapes, shades, or removable film. If you go this route, be sure to choose windows with a “Solar Heat-Gain Coefficient” that matches your climate.
One step up from blocking the sun from the inside of your windows is to keep direct sunshine off your windows entirely with outside shades and awnings. Properly designed awnings can stay up all winter-the angle of the sun is lower then, so sunshine can come in when you want it. Somewhat less expensive, more portable, and less obtrusive from outside, mesh shades can be installed over the outside of your windows for use during hot weather, and removed for the heating season. Vines, trees, and shrubbery are also great ways of keeping direct sunshine off your house and yard, and they actually work to cool the air, as well! When sunshine hits their living leaves, plants release oxygen, gas, and water. As the water evaporates, it absorbs heat. While it takes a while to grow a big shade tree, in a single season you can grow annual vines on trellises to shade walls or even roofs. And fast-growing flowers like sunflowers, planted along the sunny side of the house, can create a good deal of shade along walls during the summer and early fall. In just a few years fast-growing shrubs can grow to a sufficient height to replace them. In all but the Deep South, select trees and shrubs that lose their leaves in the winter so the sun can shine through when you want some free solar heating. And make sure you plant trees and shrubbery in the right spots; a recent study found that shade trees planted on the south and west were most effective at cooling homes, while those planted on the north and east could actually increase your utility bills.
3. Insulate Your House
The fewer air leaks and the more insulation you have, the easier it will be to keep your house cool in the summer (and warm in the winter). Sealing air leaks is often inexpensive and pays off fast in lower energy bills. Adding insulation is more of an up-front investment, but can also have a pretty fast payback, as it also saves you money year-round. As you make your home less leaky, it becomes even more important not to add heat to the indoor air. The middle of a hot afternoon is not the time to roast a chicken or run the dishwasher. Save oven and stovetop cooking for summer evenings or early mornings. Use your microwave instead, or cook outdoors (our great-greats had summer kitchens in separate buildings for a good reason).
If You Have To Use AC
Depending on where you live and how your house is designed, you may decide you need at least some air-conditioning to make it through the summer. Save money on electricity and keep your environmental impact as low as possible by doing everything I’ve already suggested and using AC only when you really need it. Seriously consider replacing any unit that’s older than 10 years with a new, more efficient model (this could easily halve the electricity used), but be sure to have the old unit properly recycled. Look for the Energy Star label when you buy, and get the right size unit for your space (either too big or too small will suck up more energy). Buy high-efficiency units, and look for useful features like timers and air filters (clean these as directed, for max efficiency). If replacing a whole-house unit, shop around and consider heat pump options as well as traditional condenser units. In a few years you may even be able to buy asolar AC unit, but chances are they will be pretty pricey for a while.
And rethink how cool is cool enough. Turning up the thermostat just a few degrees will save significant energy and money. Use fans to keep the air moving in occupied rooms, and you can nudge the thermostat up another degree or two. If you are away from home during the day, install (and use!) a programmable thermostat that will cool off the house just before you arrive home, instead of maintaining a cool temperature when no one’s there. It takes more energy to keep a house cool over time than it does to cool a hot house down-and don’t let anyone tell you otherwise.
Last, but not least, embrace summer. Enjoy it-don’t fight it so hard. Think about moving your daytime activities to the coolest part of the house for summer, and/or sleeping on a screened porch on hot nights (this latter is a lovely indulgence-almost like a mini-vacation in my experience). When you get hot and sticky, soak in a cool bath, play in a kiddie pool with the kids, or even just put your feet in a basin of cold water, and sip iced drinks!  The heat is nature’s way of saying “slow down,” and we can certainly all use a bit of that!
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