It amazes me when people who really don’t have any background in science or math make these kinds of statements. While scientists and even the utility company are telling everyone to turn down the thermostat to save money, some of us choose to completely ignore this advice. Perhaps it is time to take a closer look at what is the scientific basis for turning down the thermostat in the first place.

To begin with, let us take a look at how heat escapes from your home. In any closed system, we need to know that energy is conserved. In other words, energy is neither created nor destroyed. Any heat that is lost to the outside must be made up by the furnace. In other words, if there were no heat losses, the furnace would never need to come on.

There are three types of heat movement to discuss: Conduction, infiltration, and radiation. Conduction is where heat flows through solids such as your walls and ceilings. Infiltration is where heated air escapes your home through cracks and open areas such as doors and windows. Radiation is where heat is transferred by hot and glowing objects, such as the sun as it shines on the earth from millions of miles across outer space. We will be looking primarily at conduction and infiltration. Radiation is insignificant for our study.

Heat is conducted through every surface of your home. Insulation reduces the amount of heat that can move through the surface due to conduction. The mathematics for heat conduction through a surface state that the amount of heat conducted is proportional to the difference in temperature between the outside and inside surfaces. What this means is that heat is lost through a wall at a rate that changes based on the difference between the outside and the inside of your house. So, if you lower the inside temperature of the house by turning down the thermostat, less heat is lost, and the furnace works less to maintain this lower temperature.

Heat is also lost from your home due to infiltration.

There is always some amount of cold air that makes its way into the home. Weather stripping doors and windows, and caulking to reduce cracks in the walls are common ways to reduce infiltration. The heat lost from infiltration also is proportional to the difference in temperature between the outside and inside of your home. Reducing the inside temperature of your home serves to reduce the energy loss through infiltration as well as conduction.

Homes built in the last few years are built so that infiltration is reduced to a minimum. While this reduces the heat lost from infiltration, it also reduces the positive effects of fresh air. The end result is that new homes have a very high level of indoor pollution.

The only way to reduce this pollution to acceptable levels is to introduce fresh air. This is exactly what an exhaust fan does. An exhaust fan takes the stale or smelly air from the bathroom or kitchen, and sends it outside the building. Air from outside the bathroom or kitchen is drawn in, creating a negative pressure in the rest of the home. Outside air is then drawn into the entire home from every crack or hole in the wall, ceiling, or floor. Energy is lost based on the volume of air that is exhausted.

One other misconception about how your furnace and thermostat are related: Turning your thermostat HIGHER does NOT make the furnace work any FASTER. This is something that I see now and then. When you come home to a cold house, it does not make any difference to set the thermostat above the desired temperature. The furnace does not burn more gas depending on the thermostat setting. Most all furnaces are one speed devices: either they are on or they are off. The newer more expensive furnaces can have two burner settings, or even can modulate in between. However, 99% of all residential furnaces have one burner setting and that's all. One disadvantage to setting the thermostat too high is that the furnace will overheat the house!
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