Keeping your cool is more important than ever – since this year is officially the hottest on record. Indeed, each of the last six months have set global temperature records.

Almost everyone in developed countries relies on standard active mechanical air conditioning to stay comfortable during the warmest months. It’s one of the fastest growing end uses in the energy sector and a major contributor to high home energy bills. What on earth did everyone do before the vapor-compression cycle was invented to cool our homes? The ancients dressed appropriately, designed their homes wisely, stayed in the shade, gathered around water and sought a breeze. Keeping cool in the modern world doesn’t have to be so different. Using these tried and true passive methods works today. They use very little energy and some are free. And they can be supplemented with active energy efficient mechanical cooling strategies if needed.

Cool Structures

If you live in a high performance home, you have a big advantage. The extra insulation, air sealing and high-performance windows keep the heat outside in summer, just as they keep the heat indoors in winter. Your heat recovery ventilator circulates fresh air through the building while keeping the heat outside. Facing your building toward the south soaks up sun during winter, but blocks it during summer. Properly designed fixed window overhangs help, too. In these homes the structure itself works to keep you cool. If your home lacks any of these cooling features, you may want to consider remodeling your home on the path to zero. No matter what kind of structure you live in, you can take very inexpensive – or free – cooling measures today.

Cool Behaviors

Here’s an approach that requires little or no equipment, takes little effort, and can be completely free: sitting in the shade. Your shady spots will change as the sun travels across the sky each day, so select the best spot for the time of day.

Cool drinks can take the edge off a hot day. Keep a jug of water in the refrigerator for a refreshing break. Wear light clothing to reduce overheating. Spray your face with a cooling mist from a water-filled spray bottle, apply an ice pack or a wet, cold wash cloth, or take a cool shower during the hottest part of the day.

Cool Spaces

If you don’t have shade, you can create it with an awning or umbrella. Try to block windows from direct sun to keep heat out of the house. Sun screens mounted to the windows are a good idea for east and west windows that suffer from direct solar penetration. Thinking long term, you can plant trees or shrubs to shade the yard or house. If you’re less patient, consider fast-growing climbing vines, such as wisteria, grapes or hops and fast growing trees suited to your climate zone.

Ideally, cool outdoor spaces will naturally catch a breeze. If they don’t, you can hang a ceiling fan on a covered patio or place a box fan under your favorite tree. You can also use a misting fan system for additional outdoor cooling.

Cool Nights

You may live in a place where night air is cooler and drier than during the day. If so, you can open windows at night to flush out the house, removing excess heat and preparing it for the next day. This method requires some experimentation, but a temperature difference of 15 – 20 degrees from day to night should be enough to significantly cool your home. You’ll need to open as many windows as possible to get cross ventilation and lots of air flow. A ceiling fan or portable fans to stir the air up will be very helpful. Then, close the windows in the morning to hold in the cooler temperatures during the day. Lowering the shades on any east or west facing windows will help prevent overheating during the day.

Cool Mechanicals

If these passive cooling measures do not provide sufficient cooling, you can move on to low energy use, less expensive, mechanical upgrades to more actively cool your home this summer – without using inefficient standard air conditioning.

You know that a breeze blowing across your skin feels good on a hot day. Moving air pulls heat away from your body faster than still air. Fans create an artificial breeze that helps your body’s own cooling system – your skin – work better. While a simple fan can make a big difference in your comfort, it uses very little energy and costs much less than an air conditioner.  Fans do not reduce the air temperature in the room, so they only work when you are there to enjoy the benefit. And since a fan motor generates a small amount of heat that warms the room, you should run a fan only when people are present. You can use either a permanent-mounted ceiling fan or one or more portable fans.

Another energy efficient mechanical option is evaporative cooling. Sometimes called “swamp coolers,” these devices cool air by evaporating water. While the image of a swamp cooler may not seem glamorous, in the right climate zones they are very effective. They are less expensive to purchase and operate than a standard air conditioner. Evaporative cooling works best in areas with low relative humidity during the cooling season. Deserts and “mediterranean” climates, such as much of the Pacific coast, are very suitable for evaporative cooling. The downside of using water for cooling is… using water for cooling. In many dry areas, where the climate is well suited for this approach, there are also severe water shortages. Newer technology called two-stage evaporative cooling can be more efficient for very hot climates.

Finally, a mini-split heat pump can be installed in any climate zone. While more expensive than other methods a mini-split, which both heats and cools can easily be installed in a single room of existing homes.They are much quieter and use much less energy than standard air conditioners.

Using any or all of these energy saving suggestions, starting with the passive cooling measures, will keep you comfortable during hot summers and at the same time will help fight climate change by reducing or eliminating the high energy use of standard air conditioners.


—Bruce Sullivan, Building Science Consultant,