Stay warm with passive heating

In sunny climates such as Colorado, passive solar design is a highly effective way to keep inside temperatures comfortable year-round, cut non-renewable energy use to a minimum and live in connection to the cycles of the sun and the changing seasons. As the cold sweeps in, here are a few tips for staying warm by designing with the sun in mind.

1. Consider your climate. Sunny climates with cold winters are best suited for passive solar design. The solar gain must be great enough to offset heat loss from the use of large, sun-exposed windows. In cold, cloudy climates (such as in Scotland or in New England), or even shady valleys where direct sunlight is less available, the heat loss from large windows can become difficult to offset. In such climates, superior insulation is a more appropriate method to stay warm indoors.

 The trombe wall in this passive solar house absorbs heat from the sun through the windows and radiates warmth to the bedrooms behind the wall.

2. Use mass effectively. Heat storage is essential to successful passive solar design. High mass materials such as concrete, water, sand and masonry can absorb and store heat from the sun, and then release it gradually once the sun goes down. Trombe walls – a dark colored, high mass wall, placed behind a set of windows and exposed to direct sunlight – are a great way to absorb and store heat. The absorbed heat gradually travels through the wall and radiates warmth throughout the night to the inner side of the wall. High mass floors can also serve as heat storage. For example, we used a highly insulated sand bed below a concrete floor in the Strawbale Getaway project to provide heat storage. The dark concrete floor absorbs heat and transfers it to the sand, which then releases it over time to equalize temperature variations over the course of several days.

3. Insulate the building envelope. A well-insulated building envelope (the full periphery where the building is exposed to the outdoors and ground) is fundamental to effective passive solar design. Isolating indoor mass by using insulation on all exterior sides minimizes heat escape and improves the effectiveness of passive solar techniques. For example, heat loss through windows can be reduced with insulating curtains or blinds.

The overhangs on this west-facing residence provide shade from direct sun while framing the view of the mountains.

4. Regulate heat gain. Overhangs designed around the sun’s seasonal paths are essential to maximize direct sunlight during winter months and provide shade during summer months. Spring and fall sunlight is more difficult to regulate with overhangs alone. Shutters and blinds however, can help regulate heat gain (and loss) during the in-between seasons. This west facing home’s overhangs were designed to buffer the indoors from the western sun’s overwhelming exposure, while allowing natural light inside. The design integrated the overhangs to frame the panoramic view of the Rocky Mountains.

5. Design with convection in mind. A clever layout can maximize heat circulation and ventilation to help equalize and regulate temperatures throughout the home. For example, open floor plans will allow heat to penetrate parts of the home that are not as exposed to sunlight. Areas with less sun exposure can especially benefit from Trombe walls, which capture heat on one side of the wall and release it on the other side over time.

Designing with the sun’s path in mind will help the whole structure benefit from natural warmth and maintain comfortable temperatures throughout. Best of all, passive heating works hand in hand with passive cooling, so in case you missed it, here are some design tips from our summer post on natural cooling.