You, like many other people, believe that heating your home when you are away makes no sense, particularly since it costs hundreds if not a thousand dollars a winter season to do so. Your logic, though apparently reasonable, has unforeseen consequences.

Setting your thermostat back saves money in the short term. Unfortunately it is likely to cost you dearly over time. The problem lies in the change in relative humidity that occurs when you set back your thermostat.

Let us assume that it is a relatively dry winter with relative humidity in your northern home averaging 30 percent when the thermostat is set at 70^oF. If we now set back the temperature, the relative humidity rises to 70 percent at 50^oF and 100 percent at 40^oF. This is the optimum humidity range for mold spores to germinate and grow. In fact the minimum relative humidity required for mold spore germination and infestation of materials in your house is 70 percent.

Given an average relative humidity of 30 percent in your house during the wintertime it would be wise to maintain your house at a temperature of 60^oF when you are away during the winter season. Otherwise you may put your house at considerable risk of having a significant mold infestation problem.

How badly your house becomes infested depends on a number of factors. These include: the amount of moisture in the soil under your house; whether your house has a forced air or cable electric heating system (because of poor air circulation, a cable-heat house is more prone to mold problems); and type of materials present (books, paper materials and older carpets are more prone to becoming infested). Depending on the severity of the problem, mold may be found growing on walls, doors, carpeting, clothes, books, etc. Sometimes it is obvious in that you can see mold growth in the form of dark or very white spots. In many cases you can’t see it, but you can smell it. If your house smells musty, then obviously it’s there.

You may say what’s a little mold, I’ll just wipe it off. Unfortunately, in many cases, it is not that simple. Mold is often difficult to control, particularly when it is caused by low set-back temperatures (since infestation is often so extensive).

Mold may be a problem in that your house, in whole or in part, smells musty. Though the odor is not known to cause any adverse health effects, many people find it to be unpleasant.

Mold may be a health problem because individuals may become sensitized and develop allergy symptoms, and in more severe situations, asthma.

Because of the risks involved (musty odor, mold growth, respiratory symptoms) using low set-back temperatures to save on heating costs is simply not worth it.