The Thermal Mass Myth
There is a lot of misinformation and misconceptions on the topic of thermal mass and logs for log homes. What we hope to accomplish with this information page is to clear up some of the fallacies and myths often encountered when discussing thermal mass and logs.
Let’s begin by clearing up some thermal mass misconceptions.
Thermal mass is not insulation. Thermal mass is actually an estimate of a material’s ability to store and release heat. Logs do have a thermal mass, but so does concrete, stone, masonry, glass. In fact, all materials have a thermal mass.
Thermal mass is not used to calculate a materials R-value. R-value is actually a measure of thermal resistance.
One myth that is often heard is that you do not need to be concerned about the r-value of logs and their thermal mass characteristic’s replaces the need for insulation.
This is just not true.
Here are some comments you may hear in a typical response to:
“What is the r-value of your log?”
Wood is a natural insulator. While this is a true statement, it does not tell you anything regarding r-values. You are being told this in an effort to avoid having to answer your question.
Logs hold heat naturally. It is a piece of wood. No more than that.
Log homes have been lived in for years. True, but they were not energy efficient then or now. New technologies can make them significantly more energy efficient.
To put it in simple terms, thermal mass as a means to store and release heat is great, but only if you are not buying the energy to produce the heat that will be stored in the log. If your log wall is absorbing heat from your furnace and slowly releasing it back into the living space of your home, it is also releasing that stored heat at the same rate to the outside. Logs are not smart. They do not know the inside from the outside of the wall. That is your energy dollars being radiated to the outside of your home.
Another important factor to understand is that insulation does not store heat. Insulation deflects heat and slows its migration. Insulation works in the daytime and at night. In the northern latitudes, there are many more hours of projected heat loss for a home during the heating season than there are hours where you could expect a heat gain from solar energy. The more heat generated with your energy dollars that can be retained in the interior of your home the better, and the less energy dollars wasted.
The U.S. Department of Energy has published that a log’s thermal mass can affect an apparent gain of 0.1 r-value per inch in appropriate conditions. That’s 1/10 of an r-value. I can speak from personal experience, having been born and raised in Michigan, there are very few days during the heating season that there is sufficient sunlight to accumulate any appreciable heat gain. All of the heat needed is coming from sources created with your energy dollars, and all of the heat loss also comes from those same sources. You need less heat if you don’t lose it to the outside. Insulation slows the migration of heat. If you need less heat, you pay lower energy bills. Insulation allows more of your heat to be kept in the home.
Call me or send me an e-mail.
Phone: 231-670-2886
chris@greatlakeslaminators.com
Let me show you how insulated logs are free. The energy savings are real, can be proven, and are calculated. There is no guesswork.
Online resources:
http://en.wikipedia.org/wiki/Thermal_mass
http://en.wikipedia.org/wiki/R-value_%28insulation%29
http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10170