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Bathroom exhaust fans are not expensive to run when they are working only when necessary. On average it costs $3.5 per year to run a modern correctly sized fan. Heated bath fans are much more expensive to run costing an average of $113 per year.
With rising energy prices and everybody looking to conserve energy to keep our planet clean, it’s wise to analyze everything that consumes energy in our households. Sometimes it’s the smallest things that you don’t even think about that make a big difference!
How Much Electricity Does a Bathroom Fan Use?
Here is a table demonstrating how much electricity bathroom fans use and how much it costs to run different-sized extraction fans hourly, annually, and just for the sake of it, for 10 years. This is the average expected lifespan of the fan.
|CFM||Wattage(watts)||Hourly cost(USD)||Annual cost(USD)*||Lifetime cost(10 years)*|
*1.5-hour usage per day (3 person household, 10 minutes during shower + 20 minutes after the shower, times three showers)
**Electricity cost $0.1285/kwh (Source)
**Heated fan with a 1600 heating element
How Many Amps Does Bathroom Fan Use?
The word “Amp” comes from the French ampère, meaning to measure. An Amp is a measurement of electrical current and can be obtained by dividing watts by volts.
Example: A 36-watt bathroom fan in the USA (120v) would be: 36/120= 0.3 amps
An average residential bathroom fan draws 0.3 amps. The amperage is so small that it is not worth considering when calculating circuit loads. The amperage will affect whether the fan is energy star certified and how powerful it is. Most modern bathroom fans draw about 0.005 amps per CFM.
Older bathroom fans draw considerably more amps since the motors are less efficient and the overall fan design is poorer.
Noisy bathroom fans also tend to draw more amps. Vibrations caused by the fan make the fan uses more energy and therefore draw more amps.
Don’t worry though, there are no residential bathroom fans (except heated ones) that draw more than 1 amp.
Just to bring things into perspective, an old-school incandescent lightbulb draws more amps than the average bathroom fan.
How Many Watts Does Bathroom Fan Use?
Watt is the electrical unit for the rate at which energy is generated or consumed.
The conversion of energy into a usable form, such as movement or heat, can be measured in watts. The term was coined in 1882 and named after Scottish engineer James Watt who developed an improved steam engine with increased efficiency that had become ground-breaking to society at this time.
An average residential bathroom fan uses about 36 watts. Watts can be easily used to calculate how much energy the fan uses over a period of time.
36 watts 3 hours a day is: 36/1000*3= 0.108 kWh
Watts, amps, and volts are closely related. You can always calculate one if you know the other two.
For example, you know that the fan draws 0.3 amps and you are in the USA (120 volts). 0.3*120= 36 watts
How Can I Reduce Bathroom Fan Electricity Consumption?
Here are a few easy ways to reduce energy consumption:
Buy a Timer Switch for Your Bathroom Fan
Usually, the beginning of the day is very busy, everybody tries to sleep till the last second and it is easy to forget things.
Let’s say the morning started with the typical family’s morning chaos—everybody running around, trying to rush to work or school, and nobody remembered to turn off the bathroom fan. In that case, it would keep running all day until someone finally gets home and turns it off.
Wouldn’t it be nice in this scenario if the fan would stop working automatically after 30 minutes it was last turned on? This will not only save money but extend the lifespan of the fan.
If the fan is left on for 3 hours extra every day it will cost an additional $65 in electricity costs over a 10 year period.
Investing in a timer switch can, in the long run, save you more money than it costs. Furthermore, consider the heat loss from excess ventilation during the winter months.
Invest in a Moisture Sensing Fan
Some bathroom fans come with a really useful extra feature—a moisture sensor. This is a must for a person like me, who simply forgets to turn on the fan before showering.
The sensor is a built-in feature, so installing it is no more difficult than installing a normal fan, just make sure that you size the fan correctly to the hole in the ceiling/wall and the duct.
The sensor in the fan simply measures the moisture level in the room, and when it passes a certain threshold, it will automatically turn the fan on and keep it running until the moisture level drops back down to normal.
This ensures that the room humidity stays within an acceptable range and your energy bills stay low, even when the person using the bathroom forgets about the fan.
Clean the Fan Regularly
While the bathroom fan is doing an excellent job sucking in moisture and directing it out of your home, it is also sucking in dust and lint from the air. Over time, this will collect on the grill and blades of the fan.
As the dust collects on the fan it loses efficiency and runs longer, gets hotter, and uses more electricity in the process.
All the dust accumulation will make the fan louder too. Most of the time when people clean their fans that solves the excessive noise problem as well. In our article about why bathroom fans get noisy, we explain in more detail how to clean your bathroom fan.
You wouldn’t believe what the fan blades look like after a couple of years of neglect. I know it’s a chore climbing up the ladder and cleaning it, but it is well worth doing for more than just financial reasons.
According to the American Society of Home Inspectors, dirty bath fans can be a cause of fires. The fan relies on cool air moving over the fan motor to keep it cool. If the fan is filled with lint and dust, the airflow is severely restricted. Combine a hot motor with dry lint and you have a recipe for disaster.
Buy a Correct Size Fan for Your Bathroom
There are many different types and sizes of bathroom fans on the market today. It can be a challenge to pick the one that is right for your needs. It is wise to do some digging around and find out which one is optimal for your bathroom.
As I recently discovered when shopping for a new fan there are way too many options available with features that you will never need on a bathroom fan. This makes it difficult to concentrate on what really matters: noise level and CFM.
However, this is a generalization and does not apply to very big bathrooms or when you have multiple showers. Furthermore, if your bathroom is smaller than 50 sq. feet, the smallest fan you can install according to the International Residential Code.
My Bathroom Fan CFM Calculator makes choosing the correct sized fan for your bathroom a much easier task.
Make sure you don’t get an underpowered fan thinking it will save you money. It will struggle to dry the room in a reasonable amount of time and will cost you more in the long run. So, brew yourself a cup of joe and dive into the bathroom fan world.
How Much Does It Cost to Run a Fan 24/7?
Running a medium-sized fan 24/7 will cost around $52 a year or $4 a month in electricity costs. A dual-speed fan running on a low setting will cost around $25 per year or $2 a month.
Before you even consider running the fan 24/7, you should find out if your fan is rated for continuous operation. You can do that by finding out what model fan you have and googling for its manual. You can find the model number printed on the fan when you remove the grill.
However, most bathroom exhaust fans are not designed to be on 24/7, and keeping them on for extended periods of time will dramatically shorten their lifespan. This is especially true for the smaller, cheaper models that go through walls.
How to Find out if You Have a Heated Fan
In case the electricity cost for the heated fan scared you, I will let you know how you can easily check if you have a heated fan.
By using only the exhaust fan the electricity usage is the same as a normal fan.
By checking if one of the settings blows air back into the room you can determine if it is a heated fan. Normal exhaust fans only suck the air out of the room. There should be an extra switch for the heater so that it is possible to use the heater independently of the exhaust fan.
How Long Should a Bathroom Fan Run After a Shower?
Let us start by saying that it is important not to forget to turn on the bathroom fan before you start showering, then you can be sure that all the moist air will be directed out the moment it appears.
If you are forgetful, or if there are small children in the house then I recommend using a humidity-controlled bathroom fan or switch. This will guarantee that the fan is always turned on when the humidity level rises.
After you have finished enjoying your relaxing shower it is recommended by the Home Ventilating Institute to keep the bathroom fan on for a minimum of 20 minutes after the shower, provided you have a correctly sized fan.
However this is the absolute minimum, normally it takes at least 40 minutes to properly dry out the room. This of course will depend on your climate, the time of year, and how careful you are at drying the walls and floor after the shower. All the water on those surfaces will evaporate and can cause excess moisture build-up and potential mold problems.
Here is a picture from my smart home system that monitors the humidity in the bathroom. You can see how much the humidity rises with every shower, and how long it takes to drop back to normal.
Turning off the fan too soon or completely forgetting to turn it on can cause major problems over time including mold, mildew, and even structural damage in the most severe cases. Excess moisture can also cause allergy problems for some people.
You can read more in my article on how long should a bathroom fan run after a shower.
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