What Is a Trombe Wall?

Design

• A Trombe wall passively collects heat throughout the day and gradually releases it at night. These walls usually consist of a pane of glass separated from a thick wall by an air pocket between 1 and 3 inches deep. During the day, the sun heats the wall with infrared radiation, while the glass traps the heat close to the wall. The wall heats throughout the day and it radiates into your home at night. This heat-storing wall is called the thermal mass, and it is usually made of stone or concrete, but any dense material that stores heat will work. The efficiency of a Trombe wall is dependent on the amount of energy that the thermal mass can store and the amount of heat it can collect through the glass. Increasing the size of the glass to allow more light to strike the thermal mass will increase the efficiency of the wall.

Orienting the Wall

• The orientation of a Trombe wall is an important consideration, due to the shifting position of the sun throughout the day and over the course of the year. Trombe walls trap the most heat when the window portion of the wall is facing toward the equator. In the northern hemisphere, Trombe walls facing south with an angle of less than 5 degrees away from true south are the most efficient; however, windows that face within 15 degrees of true south are still effective.

Alternative Designs

• Trombe walls typically cannot begin delivering heat until several hours after the sun begins heating them. Some designs include a vent that pipes warm air from the space between the glass and the thermal mass directly into your home, allowing the Trombe wall to work much more quickly. Other designs use painted walls to increase their rate of heat absorption, while some designs focus on alternative materials. Some Trombe wall designs use a sealed container of water in place of a stone wall to decrease the overall mass of the wall.

Considerations

• Using double-paned glass will prevent heat from escaping your Trombe wall and will greatly increase its efficiency. Make sure that the air pocket between the glass and the wall is completely sealed to prevent heat from escaping through gaps. Some windows use low-emission glass that is specially designed to block infrared radiation. Avoid using this type of glass in your Trombe wall, since it will prevent the wall from heating properly. These walls are most effective when the thermal mass is not separated from the interior of your home by a layer of insulation and drywall.