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How can you use the sun’s path over the winter to make your home warmer? Take a look and see how you can use passive solar energy to heat your home for free.

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Now that the sun is dropping in the sky in the northern hemisphere, pay attention to how it falls on your house and into existing windows. Over the next six months, watch the sun’s path and its play inside and out. Use that information to install windows and thermal mass for passive solar heating.

Use ancient knowledge

Solar energy is as old as the sun itself. For thousands of years, it has been heating and cooling the earth and people’s living spaces. Indigenous people of North America built their dwellings into the sides of south facing cliffs. The low winter sun penetrated and heated the space. The rock walls absorbed the heat and radiated it back out at night for warmth after dark.

The spaces were carved far enough into the cliff to create an overhang. The heat of the high summer sun was not allowed to enter. These passive solar design principles are still in use in modern architecture. Take advantage of ancient knowledge to help heat your home.

Window placement

Windows must be placed where the most winter sun hits exterior walls. South facing walls are obviously the best choice. They receive the strongest sun of the day. Windows on east walls let sun in early to begin heating the house. Afternoon sun is the hottest, and west-facing windows will add to the day’s warmth before the sun sets.

Be careful adding windows on the west, because just as that side is hot in winter, it will be hotter in summer. Consider planting shade trees on the northwest side of the house. Shade trees to the northeast will also keep the sun from heating your home on summer mornings.

Types of windows

Windows are made for specific regions of the country and applications in your home. They are also labeled for energy efficiency.

The U-factor rates the window’s heat conductivity. It can pertain to the glass, the frame, or both. The lower the number, the more efficient the window is.

The Solar Heat Gain Coefficient (SHGC) tells you how much solar radiation becomes heat in the house. Look for a high SHGC number.

Visible Transmittance (VT) is the amount of light available to the eye. The rating takes into account daylighting needs and glare reduction.

Air Leakage is air movement around and through the window. A low number shows less air leakage.

You want the most light and heat to enter the home, and as little as possible heat loss. Find a sample window label on the Energy Star website.

Get more detailed information from the National Fenestration Rating Council (NFRC) and Energy Star, and consult a local window specialist.

Thermal mass

Harness as much of the sun’s energy as possible with thermal mass inside the house. The sun will warm it during the day and release it out into the living space at night as temperatures drop. Thermal mass gives off a more even and gentle heat than an air duct or space heater.

The most effective passive heating materials are concrete, tile, brick, stone, earth, and water. A bare, dark, concrete floor is probably the most efficient. Windows need to be placed for the sun to hit it directly.

Interior walls of concrete, stone, or adobe where the winter sun can reach them, will be attractive and functional as a heat source.

Save more than once

The sun’s energy is free and constant. Take advantage of it! Save money on your heating and lighting bills while preserving natural resources.

Before adding energy saving measures to your home, tighten it up and reduce air leaks with caulking, weather stripping and insulation. Protect your solar investment!

Check for tax credits and incentives from DSIRE and your local utility to keep on saving. Paybacks are high when you use passive solar heating.

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.