How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is the difference between ON and AUTO on a thermostat?
Monday, October 1, 2018
ON vs AUTO Pro and Con
These two settings control the blower in your heating/air conditioning system. When “ON” is selected the blower runs continuously, even when the system is not heating or cooling. With “AUTO” selected the blower runs only when the thermostat activates the system for heating or cooling. Both selections have advantages and disadvantages.
Advantages: continuous filtration of air, and circulation prevents room air from stratifying—where the warm air collects at the ceiling and cool air settles at the floor. Also, the on/off cycles of the the heating/cooling system are not as noticeable when the blower runs continuously.
Disadvantage: Uses more energy than “AUTO.”
Advantage: more energy efficient mode than “ON.”
Disadvantage: Less air filtration, possibility of stratification of air—especially during winter heating months in rooms with cathedral ceilings.
While it might seem that setting the blower at “ON” to run continuously would reduce the life of the blower motor, that’s not necessarily the case. Motor life is reduced more by the repeated on-off cycles of “AUTO” that the extended time running in “ON.”
Even if you normally set the blower at “AUTO,” when you have an odor problem, consider putting an activated-charcoal type filter in your filter slot, such as the 3M Filtrete Odor Reduction Filter, then setting the blower at “ON” for several days to assist in getting rid of the smell.
Also, see our blog post What does "AUX HEAT" and "EM HEAT" on my thermostat mean?
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To learn more about heating and air conditioning systems, see these other blog posts:
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