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High Mass Solar Thermal Space Heating

One of the oldest known man-made solar thermal space heating systems was built by the Romans, who constructed radiant floors for their bathhouses over 2,000 years ago. The systems heated the bathing water and the buildings by circulating hot air under the floors, then up through multiple chimneys. Today, radiant floors are not only the most comfortable heating system available, but the most economical – especially when tied into solar thermal heat generation!

Liquid-Based Solar Thermal Systems for Space Heating

Active solar thermal installations come in two main types for space heating: liquid-based and air-based. The third type – high-mass systems – is completely different to active systems and deserves separate treatment.

High Mass Solar Thermal Space Heating Layout

High-mass installations use a sand bed or pit underneath the building and a network of Pex tubes to gather, store and deliver heat to a radiant floor. They are extremely economical to run and provide very comfortable heating for the whole home. Remember to complete your installation in spring, so that the system starts gathering heat as soon as possible!

Liquid-Based Solar Thermal Space Heating Systems Without Storage

The simpler option for solar thermal space heating is to install what's known as a "dump" system. In this setup, there is no storage tank: the collectors heat the domestic supply when the sun is shining and send that heat to some kind of liquid-to-air interface, such as a radiator, a baseboard heating unit or a fan convector.

Living with High-Mass Space Heating

Although they are extremely efficient and produce very comfortable radiant floor heating, high-mass solar thermal systems can be difficult to live with, especially at first. They require changes in habits and it may take a few years to figure out the optimal approach for your particular situation. This article will provide the background knowledge and some pointers to help you along the way.

Drainback Solar Thermal Space Heating Systems Without Storage

Drainback systems work very well for space heating applications without storage because, once they reach the target temperature, they can just switch off. All the solar fluid drains out of the pipes and collectors, meaning there's no risk of overheating, even during very hot periods when the system is inactive all day.

Air-Based Solar Thermal Space Heating

One of the most cost-effective alternatives to both liquid-based and high-mass space heating systems is an air-based installation. This is because the equipment used is relatively cheap and simple, and the transfer medium has no special requirements. Air-based systems cannot be used to heat a domestic water supply, but work well for space heating.

Pressurized Solar Thermal Space Heating Systems Without Storage

Pressurized systems for space heating are very similar to drainback installations, though they have additional considerations because the solar loop is always full. Unlike a drainback system, they can't just be switched off. This puts the system at risk of overheating during the hot months when it is not in use (assuming it is not drained).

Types of Air-Based Solar Thermal Space Heating

Air-based space heating systems work very well in areas with high load requirements and, although they cannot be used to heat a domestic water supply, can generate as much heat as a liquid-based system. They are also very cost-efficient because the equipment is simpler and cheaper. Air-based systems come in two main types.

Storage Tanks for Solar Thermal Space Heating

In general, solar thermal space heating installations that include storage use either water or sand as the heat storage medium. They use one big tank or a series of smaller ones plumbed together to provide the same volume of storage. If the system uses a single tank, it's generally unsealed: the tank can be opened without affecting the system, unlike pressurized tanks for domestic hot water applications. Both drainback and pressurized solar thermal systems can use storage tanks for space heating purposes.

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