Retrofits for Passive Heating

multiple layers of insulated wall next to cozy living room

As homeowners look to find cheaper and more environmentally sustainable ways to control the temperature of their home, passive heating is becoming very popular. Passive homes are designed with the building envelope in mind, and how best to contain or keep out hot and cool air. This article will take a look at the different ways the average homeowner and DIYer can retrofit their home with passive heating.

What is Passive Heating?

Essentially, passive heating utilizes sun exposure as best as possible, keeping heat in and out as needed. For any passive heating system to work, the first step is to gauge where your home is in relation to the sun and capitalize on the hours of sunlight. The angle of the sun shifts as the seasons change, which most people will be well aware of if they deal with extreme temperature changes.

Ideally, smart passive heating design will consider how the sun is lower in the sky in winter months and higher in the summer. Passive solar heating systems will take seasonal change, sun angle, hours of sunlight, and temperature into consideration when constructing the best retrofits. Systems will vary depending on climate and location.

wall of windows with bright sun coming through over hills of trees

The Power of the Sun

Solar energy is a major component of properly designed passive heating systems. By capturing sunlight through properly placed windows, using thermal mass, and other passive heating designs and systems, there are many different ways to use one of the earth’s greatest heat source: the sun. As sunlight enters the home through windows the area is heated.

This heat then dissipates as the sun lowers and temperatures drop. Specific structures called “thermal mass” can be utilized to store this heat and disperse around the home. Concrete, brick, and containers of water are examples of thermal mass, and will slowly release the heat they capture back into the space.

Trombe Wall

A Trombe wall is a popular design that uses “thermal mass” and sunlight. This kind of wall made of brick, concrete, or other masonry is built so that it is south-facing and either painted a dark color or using dark materials to best absorb sunlight. It is then covered completely by windows or glass, separated by only a few inches in between. As sunlight enters through the glass, the Trombe wall soaks in the radiant heat where it is stored and slowly released through vents into the space behind it.

The heat disperses gradually, meaning most of it heats the home toward the evening as the sun descends. The heat is kept from leaking outside by the glass and the air space between it. When properly done, a Trombe wall can reduce your home’s energy consumption by around 30 percent.

Thermal Siphons

Sunlight can also heat up water very quickly and thermal siphons take advantage of this. These solar water heating systems are usually quite simple to construct and do not need a lot of materials. A tank that holds water must be installed above a “collector” which then transfers heat into the house. These tanks should be protected or insulated in cooler temperatures so that there is no risk of freezing or bursting.

solar water heater mounted on a tile roof

Thicker Walls

For homes that experience cooler temperatures, investing in thicker walls all around the home can save thousands a year in heating costs by adding more layers of insulation (either foam, cellulose, or bats) and covering them in properly sealed materials that won’t let heat escape. Most homes don’t have the extra square footage to allow this to happen on the interior (you need at least one foot) but a simple way around that is to add layers to the outside of the home. This method also helps cool your home in times of extreme heat, as well.


Windows are a primary feature in solar passive heating design since they are the main way that sunlight enters and heats a home. South-facing windows can be added to a home’s space so they are in direct view of the sun and its angle, exploiting as much heat as possible. If it is not possible to add windows due to budget or other concerns, existing windows can be replaced and updated to triple-paned varieties that are installed, sealed, and fitted properly for reduced air leakage.

windows with sun coming through from a snowy winter forest

Many newer environmentally designed windows will reduce glare and over-heating as well, or if there are particular areas of the home that are prone to overheating, these windows can be tinted. Other solutions for controlling glare are using shades, thermal curtains, and blinds. On the flip side, these are all great solutions for keeping cold air out when the sun goes down.

The Building Envelope

Smart passive heating design will take the “building envelope” more seriously than basic construction does, which usually just barely passes codes. Taking the time to plan out where windows, shaded areas, trees, roof lines, sun exposure and other spacial elements is one of the best ways to utilize passive heating in the most natural way.

Sealing the building envelope, where air transfers in and out of your home, will then help contain the natural heat brought in by sunlight, and will also keep cool air in when necessary. Focusing on materials and design with the building envelope in mind will directly affect how much money is spent on heating and cooling your home.

The majority of American homes will benefit from solar heating retrofits, since 60 percent receive enough sunlight to make the cost worthwhile. The majority of passive heating systems will be more beneficial to homes in climates that experience greater changes in temperature between day and night, and summer and winter.

Many aspects that will help heat your home will also help cool it, and most are common sense and a matter of good planning. Not every retrofit will benefit every home, but every home will benefit from some kind of passive heating retrofit—it’s just a matter of figuring out which one is right for you.