The Basics of Passive Solar Home Design

Enlarge Image Image Gallery Passive solar design helps homes capture and store heat from the sun. Photo By Andy Mattern

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Passive solar design allows homeowners to heat their homes naturally, dramatically reducing dependence on costly heating systems and environmentally damaging fossil fuels. The most cost-effective solar technology on the market today, passive solar design could save you tens (if not hundreds) of thousands of dollars over your home’s lifetime—without a large investment.

Homeowners have three passive solar design options:

Direct-gain design, the simplest and least expensive option, incorporates lots of windows on a home’s south side, allowing the low-angled winter sun to enter, turning the home into a huge solar collector on the coldest days.

Indirect-gain design captures the sun’s heat through south-facing glass and includes a thick wall of brick, concrete or cement blocks (known as thermal mass) immediately behind the glass. During the day, sunlight streams through the glass, heating the thermal storage wall (also referred to as a Trombe wall after the French engineer who developed the technology), then radiates into adjacent rooms, gently heating them long after the sun has set. Installing windows or vents in the Trombe wall accommodates direct daytime heating. Solar radiation warms the air, which expands and rises through the top vents to heat adjoining rooms. Cool room air enters through lower vents and is heated, creating a thermal convection loop.

An attached Sunspace­—or solar greenhouse—moves solar-heated air into nearby rooms with help from a quiet thermostatically controlled fan. Poorly designed sunspaces can overheat in summer and become extremely cold at night in winter. Consult a knowledgeable solar designer before you add one to your home.

Making passive solar work 

The best solar homes are rectangular in design, allowing the largest possible south-facing surface. A solar designer or an architect with experience in passive solar design can help calculate how much south-facing glass to incorporate, based on your climate. Most homes in colder climates require south-facing glass to make up 15 to 18 percent of total square footage. Warmer climates require less heating, and therefore less south-facing glass.

Rooms that require the most heat, such as living rooms and home offices, are typically located on the home’s south side. Rooms that require less heat, such as bedrooms and utility rooms, or those that generate their own heat, such as kitchens, are typically located on the north side.