How Much Money Can a Whole House Fan and Attic Fan Save Me on My Electric Bill?

Now’s the time to start thinking about saving money on cooling your house this summer. It often hits the upper 90’s and even breaks the 100 mark during the summer months, especially in June and July, here in Northern Arizona.

APS (Arizona Public Service), the local electricity service provider here in AZ, knows that those temperatures require a lot of power to cool. They even provide service plans to help make it easier for you to pay for the extra cost.

One of the best ways to save money on cooling your house is to install a whole house fan along with an attic fan. These fans keep you from needing to run an A/C unit at all hours of the day, which will save a lot of money on your electric bill. In this article, we’ll look at how much money whole house fans and attic fans can save.

How Much Does AC Cost to Run?

No two homes are the same and there are a lot of variables to consider when calculating the cost of running A/C. Here’s a look at what impacts the A/C cost.

Energy costs. This is the amount you pay per unit of energy. It will affect the total AC costs. Electric utility providers charge by the kilowatt/hour, or kWh. The average cost in Arizona in July 2018 was 12.92 ¢/kWh. Energy costs can rise even more due to high demand, and air conditioning is one of the greatest contributors to that demand.

AC efficiency. The cost of running the A/C unit is affected by its SEER rating. The higher the rating the more efficient the A/C unit is and the less it costs to operate. The average SEER rating between 15 and 18.

AC installation and operation quality. Other factors can affect the efficiency of your A/C unit. Dirty filters, leaks in the duct-work, and the quality of the installation can cause your A/C to run more often.

Size of your home. It’s a given that it costs more to cool more space. Larger homes will need larger A/C units, which in turn use more energy.

Outdoor temperature. Outdoor temperatures vary greatly. A/C units work harder to cool homes when temperatures are in the upper 90’s and into the 100’s. It’s even worse in high humidity. When the Arizona heat hits, the costs go up.

Thermostat settings. The temperature you set your thermostat to will determine how often the A/C runs, and on hotter days this can make it run a lot.

Calculation the Cost

We can use this information to help us calculate the A/C operation cost. Find the kWH by dividing the wattage by 1000. Multiply that by the kWH cost and you’ll have the cost of running you’re A/C for one hour.

The formula is (kWh x kWh cost) x .01 = cost to operate A/C for one hour.

Let’s use an example of a central A/C system that uses 3500 watts. This is a 3-ton unit for a 1200 square foot home, which is a common size.

3500/1000 = 3.5 kWH

The unit uses 3.5k watts per hour. The average kWH in Arizona was 12.92.

3.5 x 12.92 = 45.22.

45.22 x .01 = $0.4522 per hour.

Multiply that cost by the number of hours you want to run your A/C to get the total daily cost.

If you run the A/C for 10 hours during a hot summer day it would cost:

  • $4.522 per day
  • $31.654 per week
  • $140.182 per month (31 days)

To run the A/C for 24/7:

  • $10.8528 per day
  • $75.9696 per week
  • $336.4368 per month (31 days)

Of course, these are just ballpark figures since we don’t know the other factors, such as the outside temperature to know how long the unit with run and other factors mentioned above, but this could easily be the cost of running a central air unit for a 1200 square foot home on a hot Arizona day. The cost could be lower at night.

Whole House Fans

Whole house fans bring in cooler outside air through doors and windows and push warmer air from the house out through the attic. This makes a great impact on cooling the house, as the air conditioner doesn’t have to work with hot inside air. Whole house fans require less energy to run than A/C units.

If the air outside is cool you won’t need to run an air conditioner at all. It’s always a good idea to run the whole house fan any time the air outside is cooler than the air inside.

Whole house fans, such as those from QuietCool, can save 50-90% of A/C electricity costs. When A/C typically costs $140-336 per month, that’s a savings of:

  • $70-168 at 50% savings
  • $126-302 at 90% savings

Using a whole house fan can result in a savings of over $300 each month of running a 3500w A/C unit during the hottest part of summer. Larger homes that need larger A/C units can save even more.

Attic Fans

Attic fans cool the attic, which helps cool the rooms just under it. With attics reaching up to 160 degrees in the Arizona heat, that’s a significant temperature just above the rooms in your home. Attic fans from QuietCool have thermostats that keep the attic below a certain temperature range that you set. Their Smart Attic Fan uses between 15 and 140 watts.

Attic fans help cool the living area of your home indirectly. Due to many factors, such as the home’s materials and design, their hourly energy savings is more difficult to calculate directly, but they do contribute to energy savings.

They have a greater impact on the lifespan of the components in your attic and roof, and they make a big difference for a relatively low price when compared to air conditioners and even ceiling fans. They work great with whole house fans to help reduce the heat in your home.

Conclusion

Although the savings can range widely depending on the size of your A/C unit and its efficiency, installation quality, size of your home, outdoor temperature, and your personal thermostat settings, it’s easy to see just how much a whole house fan can save you on your electric bill. Considering how much it costs to operate an A/C unit it makes sense to invest in a whole house fan and an attic fan.

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3 Comments

  1. Pete Rainwater

    Very well written. Plenty of information written in easily understood form.

    Reply
  2. Matt Carrell

    Realistically here folks, your maximum longterm savings would be the following setup: One or two solar attic fans (one may not be enough) and a whole house fan. Then offset the cost of running the whole house fan with a 3’x 6′ size 300+ Watt rated solar panel with MC4 connectors hooked into a plug and play grid-tie inverter plugged into a wall outlet to offset the house fan’s power usage using daylight hours and lower your total energy usage when the fan is not in use. A nice 500 Watt inverter (you always want to over-rate a bit, never run them full-bore) can be had for $100 on a good day on eBay. The MC4 connector to ring terminal adaptor cable is only $20-$30 on eBay. The solar panel prices are typically under $1 per Watt now, sometimes far less. This setup will keep the house much cooler and on averages use no extra utility energy at all as all the power consumed by the whole house fan is replaced by the panel and inverter which translates the DC panel power to grid-compatible AC power automatically. Be sure the inverter has “anti-islanding” feature so it automatically shuts down in a power outage so no utility company workers get zapped.

    Reply

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