Adding thermal mass to your home can lower utility bills and improve comfort.

Adding thermal mass to a home can improve your family’s comfort because it moderates temperature swings inside your home year-round, but particularly during the summer.

During the winter, moderating the indoor temperature swings can result in less heat being lost to the outdoors. This helps in rooms where heat is generated indirectly, such as cooking in the kitchen or bathing in the bathroom. It also helps in rooms with south-facing windows that receive passive solar heating. Instead of a low-thermal-mass room overheating and losing heat, a high-thermal-mass room overheats less and stores the heat.

This is the basic concept that keeps log homes fairly comfortable in all weather conditions. Even though walls constructed of solid logs have a low insulation R-value relative to an insulated framed wall, log homes stay comfortable. This is the result of tons of thermal mass from the heavy, solid logs.

In the summer, this thermal mass can delay the need for air conditioning until later in the day. Once the outdoor temperature drops, the windows can be opened and the thermal mass cools off overnight. Another option is to run a central air conditioner or heat pump in the morning to cool the home while the overall electricity demand is
lower. This can also reduce the peak electricity demand for your utility company during mid-afternoon.

If your house is heated with a heat pump with electric resistance backup heat, additional thermal mass is a definite plus. Heat pump efficiency and its heat output are greater when the outdoor air is warmer, such as during a sunny afternoon. With adequate thermal mass, enough heat may be stored indoors so the backup resistance heating does not have to come on or run as long when the outdoor temperature drops at night.

The keys to increasing the thermal mass in your home are to select the proper materials and incorporate as much of them as possible. The thermal mass generally should be located evenly throughout your house with more in areas where it can absorb excess heat and then slowly release it to the room air.

The thermal mass of various materials is rated by their heat capacity properties. Water has a high heat capacity of 62.4 Btus per cubic foot, compared to drywall at only 1.3 per cubic foot. Wet soil rates about 55, concrete about 31, brick is about 27, and stone/tile ranges from 18 to 36, depending upon type. Their natural thermal properties, in addition to their densities, determine the above numbers.

For new construction, install a thick concrete floor even if it is over a basement or crawl space. Precast concrete panels are a good choice. Using radiant floor heating is effective with this design. Use decorative solid brick or stone for the interior wall where the new room attaches to the existing house. Tile flooring adds additional thermal mass to the room.

To increase the thermal mass in your existing rooms, install a ceramic tile floor in the foyer. This is particularly effective if the sun shines in through windows in the door. The thickness and weight of the tile is more important than its color, although darker colors are slightly better. Ceramic tile also has a unique thermal property that allows it to easily reradiate the heat out to the room.

Decorative brick panels can be added to interior walls. Although they are not as thick as a new solid brick wall, they add some mass and look realistic. If you use a fireplace, build a thick raised-brick or stone hearth. The hearth absorbs the radiant heat from the fire and stays warm for hours after the fire is out.

In the kitchen, install thick granite, marble or slate countertops and tile backsplashes to absorb the excess heat from cooking.

Here are other ways to use thermal mass to moderate indoor temperature:

• If you hand wash your dishes, leave the hot water in the sink until its thermal mass gives off its heat to the room air as the water cools. Do the same after taking a hot bath;
• Place houseplants in large pots of moist soil around the house;
• Store water in jugs for emergencies in a closet or under the sink instead of in the garage or basement.

Send inquiries to James Dulley, Michigan Country Lines, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.