A thermal mass in the most general term refers to any mass used to absorb and hold heat. Materials with high specific heat like stone, concrete, adobe or water work best.

Thermal mass is often confused with insulation, but is distinct from it.

Thermal mass is used in and around buildings to absorb or emit heat. Internal thermal mass in a well-insulated building, such as concrete or other forms of masonry, or water, reduces temperature swings in the interior. This reluctance to change temperature is related to the specific heat capacity of the mass. Water has a high specific heat and tanks of water are often used as a thermal mass.

Thermal mass is often used in solar heating systems to absorb heat during the day and release heat into the living area during the night. The thermal mass can also help over longer periods like an overcast day. In simple solar heating systems the thermal mass may directly absorb sunlight while in more complex systems moving liquid or air is used to move heat between the collectors, the thermal mass and the living area.

Earth sheltering is another important architectural means of using thermal mass. By placing exterior walls in direct juxtaposition to earth, the thermal mass of the earth provides a fairly constant, moderating temperature so that heat flow through the adjacent wall is greatly slowed.

External links

• Thermal Mass - Energy Savings Potential in Residential Buildings http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/index.html