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The Difference Between Active and Passive Solar Heating Systems

Dean Traylor is a freelance writer and teacher who writes about various subjects, including education and creative writing.

Originally published on

Originally published on

Solar power, in particular solar heating systems, are quickly becoming a popular mode of alternative energy for residential homes and businesses. They’re cost effective, as well as environmentally sound. And, in certain cases, well concealed or melded into the aesthetics of a home or business.

Since its inception, solar heating systems have evolved into two forms: the active solar heating system and the passive solar heating system. They can be used to heat rooms within a home, create electricity or heat water within a household.

Active systems are usually direct and easy to spot. Passive heating systems are built into a building or home, and are the result of better material and technology.

Active water solar heating system - diagram

Active water solar heating system - diagram

Active Heating Systems

Active solar heating systems use various mechanisms to circulate and transport thermal energy. These mechanisms may include the use of fans and pumps, and can have a liquid based system or an air based system. Often, the active incorporates the use of solar panels that convert solar energy into electricity.

Liquid based systems usually incorporate a flat plate and evacuated tube collectors. Liquids such as water or antifreeze are often used in this process. The water gets heated through convection or by solar cells, and then, with the help of pumps, is trapped and circulated through the tubes, radiating its heat along the way.

This system was popular with the first generation solar water heater. It used a huge solar panel and circulation unit that was placed on the roof of a home. The heated water was stored inside in a water tank.

The other active solar heater is an air based system. This system uses a plate collector. The collector uses a metal plate to heat the air inside it. An electrical fan distributes this air throughout rooms in a structure. This system is not in wide use. According to contributor, Frederick Blackmon, air-based systems have lower efficiency than liquid-based systems.

Usually, active heating systems can be attached to existing buildings or homes. They can be placed on the roof, window frames, and awnings. The system can be used for heating spaces in the house or to heat a swimming pool, as well as for heating the interior water system in the house.

Floors, ceilings, and walls—especially those built with concrete, adobe and brick - are ideal areas for heat to collect

Originally posted on

Originally posted on

Passive Heating System

Passive systems don’t rely on an actual solar heating unit. In many respects, they are built into a structure. It is a direct system in which the heat is directly collected. Still, it will involve some convection – the circulatory motion of liquid or gas.

This system incorporates thermal storage material (has the ability to collect and radiate heat), the position of windows or openings, and the direction of the house in accordance to the sun. The objective is to raise or maintain thermal mass – the heat capacity of a building and its material. Material such as concrete, rocks, adobe, or brick are often considered ideal material to create this.There are three types of passive heating systems: direct, indirect, and isolated gain systems.

1. Direct Gain Design

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According a Word article, a direct gain design collects and stores heat during the day. At night the system radiates its stored heat into the living room. Usually, this type works when the surface of the roof or the walls is in direct sunlight.

A direct gain, according to the article, can exist within the confines of a structure. About ½ to 2/3 of the total interior surface area can be constructed with heat storing materials. Floors, ceilings, and walls—especially those built with concrete, adobe and brick - are ideal areas for heat to collect.

For maximum direct gain in the interior, a water wall is often a good choice. It will radiate the heat into a room at night after a day of direct sunlight. For this to work however, it has to be in a place where the sun’s rays can affect this process.

2. Indirect Gain System

According to the website,, indirect gain systems use “basic elements of collection and storage of heat in combination with the convection process” to generate heat.

Dark colors or black paint are often used on the surface of a thermal storage wall, window or floor. It collects the rays passing through the window and then radiates its heat.

This writer’s father made such a device. It was a portable solar water heater.

3. Isolated Gain System

Finally, there’s the isolated gain system. This particular design uses a fluid to collect heat in a flat plate collector that happens to be attached to a structure. The heat it produces is transferred through pipes or tubes, creating a natural convection.

This system can be used to heat a room or open space within a house. Also, this system can be used in a stand-alone system. This writer’s father made such a device. It was a portable solar water heater. It used a combination of black material, Plexiglas, and tubes to create a natural convection of heated water (which, by the way, was used to brew coffee or tea).


Active heating systems can be affixed to something and be totally separate from the structure. Passive heating systems are usually built into the structure and don’t need the help of mechanical devices.

These systems have many advantages for the consumers. They can save money on heating (in some extreme cases, even make money for the homeowner). Active heating systems are becoming cheaper to buy and use, while the passive heating system cuts down on electricity while retaining a home’s aesthetics.


This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2016 Dean Traylor

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