What is passive solar heating?

Passive solar design basics

Passive solar design starts with placing the building so its windows and main living spaces face the sun—usually south in the Northern Hemisphere.

• Orientation and aperture: Large, well-positioned windows — the “apertures” — let in maximum sunlight during winter while allowing for shading in summer.
• Thermal mass and heat storage: Materials like concrete, brick or stone inside the home absorb heat from sunlight during the day. This stored heat is then released slowly at night, keeping the indoor temperature more stable.
• Distribution and control systems: Once heat is collected and stored, it moves naturally through the home by radiation, convection or conduction. Simple controls (like roof overhangs, shades and venting) help regulate how much heat enters or escapes.

Passive vs. active solar

To understand passive solar heating, it helps to also understand active solar heating. The two technologies are similar, in both cases using the thermal energy of the sun to regulate a building’s indoor temperature. Importantly, both are separate from solar electricity, by which photovoltaic systems (solar panels) turn sunlight into actual electricity.

Many energy-efficient homes use a combination of passive and active heating systems. If you’re considering using some form of passive or active solar heating and aren't sure what kind of system would work best for your home, find a solar energy company to point you in the right direction.

Passive solar heating

A passive solar heating system captures warmth from the sun, stores it and releases it over time. In the United States, two key features of a passive solar heating system are southern-facing glass and thermal mass (such as bricks or concrete) to absorb the heat.

Active solar heating

An active solar heating system harnesses the sun’s energy to increase the temperature of fluid (or sometimes air) that’s run through a heat exchanger to heat the home’s interior. This type of solar heating is called “active” because its methods directly incorporate moving parts, appliances and occasionally other sources of power (such as electricity) rather than relying on sunlight alone.

Does passive solar heating work?

Passive solar heating works by maximizing solar heat gain in the winter and minimizing it in summer. In the U.S., passive solar heating is incorporated into building designs across the country. However, it’s far more common in areas with heavy sun exposure, such as the Southwest and coastal regions.

Homes don't need to be “off-grid” or “green-certified” to use these strategies. Elements of passive solar heating design can be very effective in pretty much any building, helping to regulate the temperature and minimize energy usage.

In regions with a colder climate and limited sunlight availability, active solar heating systems are typically more sustainable. A few main principles of passive solar heating:

1. Controlling sunlight

The most important aspect of passive solar heating is controlling the amount of sunlight that enters a home through skylights, windows and other areas. Buildings that use passive solar heating are positioned to receive the most sunlight possible, which is southern-facing if your home is located in the Northern Hemisphere.

Simple design integration often costs nothing extra while yielding long-term energy savings.

To block out summer sun, most passive solar homes have an awning or overhang that protects south-facing windows from receiving direct sunlight, allowing a building to stay cool. Buildings can also be outfitted with smart shades and other coverings to block the sun from entering through the other windows or skylights, adjusting to the sun’s position from morning through evening hours.

2. Capturing and distributing heat

Capturing solar heat and regulating it throughout the home is the key to passive techniques. One of the most popular thermal mass designs is known as a Trombé wall, explained Dan Orzech, general manager of the Oregon Clean Power Co-op, a community-funded solar cooperative whose mission is to increase the amount of renewable energy available to Oregonians.

Separate from the main living quarters, a Trombé wall collects heat, which is then selectively used or released to regulate the rest of the home’s temperature.

It’s similar to a sunroom, Orzech explained, “but instead of a whole room, it's a narrow space with southern exposure, where the sun is captured. If you have a large thermal mass to store solar energy — like concrete, brick or even water — it heats up slowly and releases the heat slowly throughout the entire course of a night.”

3. Insulating and sealing

Good insulation is also critical to keeping interior temperatures stable, with minimal heat loss or gain. New-construction buildings can minimize inefficiencies with smart framing, ducting and insulation materials — referred to as the “building envelope” — as well as good seals around windows and doors.

Passive solar heating cost

Incorporating passive solar principles, like optimizing building orientation, window placement and using thermal mass, during the design phase often adds little to no extra upfront cost.

Full passive-solar home construction comes at a premium, but energy independence and reduced utility bills can offset costs over time.

Because passive solar heating typically requires physical changes to a structure, it can be very expensive to retrofit these strategies into an existing home or building. For this reason, most passive solar heating techniques are applied to new-construction homes during the building process, and they do mean increased material and labor costs.

While the exact expense for passive solar heating components is highly dependent on a building's size, all passive solar systems are designed to minimize energy use (and therefore reduce utility bills) over time. As a whole, passive solar heating is not expensive when weighed against future cost savings on utility power.

Bottom line

Passive solar heating is a lot less complicated than it may seem. If you’re building a home with passive solar heating components, such as large windows, heavy insulation and concrete or brick walls, it may increase construction costs, but you'll be able to minimize energy usage and save money on ongoing monthly energy expenses over the long term.