I get that question a lot. Here’s my answer based on research and experience. The advantages of running the furnace fan 24/7 are as follows:
- 1) you can maintain equal temperature and humidity throughout the house.
- 2) you avoid stale air spots or rooms.
- 3) by doing so research says that you can save a few heating or cooling cycles daily thus saving some energy. (at least it works in the lab.. )
The disadvantages are as follows;
- 1) unless you have an ECM or DC variable speed furnace blower motor you will spend more in electricity-substantially more. The difference in annual electricity consumption between a regular PSC blower motor and an ECM or DC variable can be as much as $300 a year at 9 cents a kwh.
- 2) you will wear down that blower motor faster. Also the computer that controls it(if you have one)
- 3) you will attract more dirt in your duct system and if you don’t have a decent furnace filter into your furnace as well. In this case the danger of plugging up the secondary heat exchanger of a high efficiency furnace and the a/c evaporator coil is greater and very probable. That will eventually slow down air flow with the possibility of irreversible damage to the furnace and a/c and with reduced air flow comes greatly reduced comfort and efficiency.
- 4) you will need to change or clean that furnace filter more often. At least every 2-3 months (depending on number of occupants and pets in your home). If you want to run the furnace fan all the time keep in mind the above points.
If you want to run it sometimes but not always there are thermostats now available that will run the fan for a certain amount of time every hour, or some hours of the day, and some days of the week. That amount of time and frequency are selectable. The fan speed at which this will happen depends on your furnace.
Bottom line is that if you are in the habit of running the fan all the time you will save electricity if you use an ECM or a DC motor but you will use more gas for heating with an ECM/DC motor. Studies on the impact of ECM motors during summer cooling have yet to be made public-to my knowledge at least.