Can Running the HVAC Fan Continuously Save on Energy Costs? Part 1 of 3
The following question was submitted to our website recently and we thought that perhaps others might be interested in the answer:
"Hello, I have a question, how much more electric do you use with the fan On vs Auto? I leave my fan On to keep the air circulating. I've heard everything from the AC pulls in outside air, which I know it doesn't, unless a door is open... to it costs just as much to run the fan On as it does when the AC is also running. I thought the fan was a low power unit, like 12volt."
Great question! To answer it, I am going to assume we are talking about a central air system with the blower motor (fan) located inside the home. These are usually closed loop systems that circulate conditioned air (hot or cold) throughout the home using wall, ceiling, or floor vents. There are larger vents, usually one per floor, that collect air and return it to the fan to be re-conditioned and then distributed througout the home again. There is a filter in the loop, usually located in the air handler where the fan is located. The filter cleans the air before it is re-distributed.
So the fan moves the air throughout the home with the help of the duct system. There are two types of fan. One runs on AC voltage and the other runs on DC voltage. You are more likely to come across the AC type, so let's use that as the example. A typical AC fan motor uses about 500 watts when it's running. We are not going to worry about efficiencies or power factors for this simple example, although they do impact the numbers slightly. So, if you run the fan continuously for a month (there are 730 hours in a month), you would use 500 watts x 730 hours = 365,000 watt hours. This is usually converted to kilowatt hours by dividing by 1000. So the fan uses 365 kWh every month when used continuously.
What's the cost? Well, the average cost of electricity in the US is 12 cents/ kWh. So it would cost about $44/mo to run the fan continuously.
In the Auto mode the fan only comes on when the heating or AC comes on. The cost of running the fan intermittently will be less, but depends on the on/off ratio. If we assume 12 hours on and 12 hours off each day, the cost is reduced by 50%, or about $22/mo.
If you do decide to run the fan continuously, there are a few important things you'll need to consider first. We'll discuss those in part 2.
Comments
Energy Use of Woodstove Blower Unit
Great questions Karen.
Does it use less energy to run the blower fan at a slower speed? The short answer is yes. Your husband is correct about the resister analogy, but in order to make the motor run slower, you need to reduce the amount of current being supplied to it. Reducing the current also reduces the energy used. Also, consider the resistance, or drag, caused by the air when you run a fan faster. It requires more work from the motor to push those fan blades through the air the faster it spins, and this takes more energy. So, slower fan speed means less currrent, less air resistance, and therefore less energy use.
Does the speed of the fan have any impact on the motor's life? Yes, running a fan motor slower will increase the service life of the motor. Running slower means fewer revolutions which means less wear and tear on the bearings.
The last question is a bit more tricky. System design is very important when using only one temperature sensor in this type of system. Assuming there is only one sensor? Without know more about the particular system and it's blower vs firebox configuration, it's difficult to make any recommendations. My advice would be to contact the manufacturer, or an authorized service provider, and explain the problem to them. They will be able to make the appropriate recommendation.
Energy Use of Woodstove Blower Unit
We purchased a blower for our Avalon woodstove that has a tempreture gauge to automatically turn it on or off. Additionally there is a manual control that looks like a dimmer switch between the wall and the blower to manually turn the blower on or off, and if it is on to adjust how hard the fan blows. My question (1) is whether or not it actually uses less energy when it is on low than when it is on high. My husband said it is just a big resister and doesn't lessen the energy consumption, so no electricity is saved by running it on low--to just decide how loud you are willing to have it. So then my question (2) is if he is correct, is there any speed that is better or worse for the motor life? (3) Is there any reason not to change the temperature gauge that came with it? The firebox is completely brick lined so by the time it gets warm enough to engage the one they provided, the fire is really hot and the air really hot, but by the time it turns off, the air is cold. I wonder if finding another gauge that can be located elsewhere in or on the stove might make the air output more uniform.
Variable Speed Fan systems
Both my upstairs and downstarirs systems have variable (multi-speed) fans and the slow speed would obviously not use as much energy as full spped on a single speed system.
With a large open area between floors (2-story lining area) I believe the comfort level (evening out air temp) benefits from having the systems run continuously winter and summer.
Ceilings fans also contribute for individual rooms as well.
When fan runs, air feels cold
If you have a heat pump, it is normal that the air feels cold. Actually, it's one of the characteristics of a heat pump system that some people don't like and we always get questions about it. Heat pumps put out warm air in the heating mode, but the temperature of the air it puts out is in the high 70's or low 80's. This is perfectly adequate for maintaining a room temperature of 73 for example, but the air coming out of the register will feel cold to you because your body temp is in the 90's (assuming you are breathing and have a pulse). So turning the fan off would esentially be turning the heat pump system off and then it would not be heating your home at all. On the other hand, if you have a forced air furnace and the air feels cold in the heating mode, you should consider scheduling a service call with your local qualified HVAC contractor for an evaluation of the system.
the fan
okay, my fan is set on auto and it is currently winter where I live and it circulates but the air is cold making the rooms cold, and I only have the "on" or "auto" options...I would prefer to not have the fan on at all to be honest, but I am not sure what to do about that...is there a means to overide this option and have it off, because the heater will warm up the room nicely, then the fan clicks on and cools everything..uugghh!!!
Wood Stove
I would recommend that you contact a local qualified HVAC contractor and have them evaluate your setup.
Continuous Fan
I have a wood stove with a hood that connects to my air return (inlet)
, I block off the return so it pulls air from hood over wood stove and keep the "fan" running continuously. Is there a more efficient way to distrute the hot air from the wood stove. Also the hood is about 2 feet off stove I was thinking about lowering it. Help me save electric! Handler is a Heil model NEBH034LKAMO motor 1.5 HP
All fans have auto?
All fans operate intermittently, that is, they only come on when heating or cooling is asked for by the thermostat. Some systems include an over ride switch allowing you to turn the fan on at any time and leave it on if you choose to. It sounds like you are describing the over ride switch.
All fans have auto?
Do all fans have an auto setting? it seems like mine only has an on/off toggle switch.
The temperature.
The Fan Continuously...
The Fan Continuously