Ask Focus on Energy

Depends on the fan, cost of electricity and how it’s used.

The cost of operation will depend on the fan, the cost of electricity and how the fan will be used.

Most people think of using a box or oscillating fan when the weather gets hot.

1. A box or oscillating fan will use about 100 Watts. If the fan was turned on for 24 hours, the fan would use 2,400 watt hours or 2.4 kilowatt hours (kWh). At $0.10 per kWh that's $0.24 a day. A window fan (the kind with two fans in it) will use about twice the energy, about 4.8 kWh or $0.48 per day.
2. An ENERGY STAR® qualified ceiling fan uses only about 40 Watts. If left running for 24 hours the fan would consume 0.96 kWh or just under $0.10 per day.
3. A window, box, oscillating or, even better, a ceiling fan can be used to reduce your air conditioning by allowing you to be comfortable when setting your thermostat at a higher temperature, up to four degrees higher. This will save you electricity and money. But remember, ceiling fans only cool people not rooms; turn off the fan just like you turn off the light when you leave a room. View these fact sheets for more summer cooling tips or the energy usage of other appliances.

Another common fan is the one found on your furnace or heat pump. Running the fan on your furnace continuously will consume more energy, and more money, than running the fan only when needed for heating and cooling. In addition, continuous fan operation can actually increase the relative humidity in your home when the air conditioner is turned on. While your air conditioner is running, moisture builds up on the coil above the furnace. In order to complete the dehumidification process, this moisture must drip off during the system’s rest period between cooling cycles. If the fan runs continuously, the moving air will re-evaporate this moisture into your home. Your air conditioner will then be forced to remove that moisture again when it turns back on, wasting energy and costing you money.

• A single-speed or multi-speed furnace will draw about 500 Watts. If left running for 24 hours the fan would consume 12 kWh or $1.20 per day.
• A variable-speed furnace will draw about 100 Watts. If left running for 24 hours the fan would consume 2.4 kWh or $0.24 per day.

Variable speed motors do draw very little voltage but even that little amount of voltage running continuously can add up to be almost $75 each year! Try setting the thermostat switch for your fan from “on” to “auto”. You really shouldn’t notice a difference in the comfort in the home. If you do notice a difference, consider having in-home evaluation with a Home Performance with ENERGY STAR® consultant to identify the cause of problems in your home and provide you with a better solution.

Published Wednesday, August 26, 2009