How to Use A Whole House Fan – 8 Steps

Whole house fans are easy to use. When used correctly, they help to cool the house and reduce air conditioning costs. But many people are not exactly sure how to use a whole house fan.

So here is a step by step guide on how to use a whole house fan.

Step 1: Check outdoor temperature

Before using a whole house fan, make sure that the temperature outside the house is lower than the inside. Since whole-house fans cool the house by replacing the air inside with that outdoors, they are effective only if the outside air is cooler. Therefore, it makes sense to do a temperature check before turning on your fan. The best times to run a whole house fan are the early mornings, evenings, and nights when the outdoor temperatures are cooler.

Step 2: Make sure your air conditioner is switched off

Whole house fans suck the air out of your house. So if your air conditioner is switched on, the fan will remove that cool air from the house, which is counterproductive. So you cannot have an air conditioner and a whole house fan working together. Before switching on your whole house fan, make sure that the air conditioner is switched off.

Step 3: Open a few windows

As mentioned above, whole house fans draw air from the outside. And this air is drawn through the windows and doors of the house. So it is important to open a few windows before starting the fan. Since these fans are very powerful, running them with closed windows will create negative pressure inside the house, which can adversely affect the working of furnaces and HVAC appliances.

Step 4: Close fireplace dampers

If you have a fireplace, you know that it is full of ashes and soot. As whole house fans create a negative pressure inside the house, which is enough to draw outdoor air, it is very likely that this soot and ashes will be blown throughout the house unless the fireplace dampers are closed.

Step 5: Close the attic stair if you have one

Whole house fans push the hot air into the attic. If the attic stair is kept open, this air will be recirculated into the house instead of being removed to the outside through the attic vents. This is counterproductive, and it hugely affects the efficiency of the whole process. So the attic stairs must be insulated and closed before starting a whole house fan.

Step 6: Turn ON the whole house fan

Flip the switch and run the whole house fan at its highest speed for around half an hour or so. Once the home is cool enough, you can change the speed to a lower setting to reduce the fan’s energy consumption.

Step 7: Run the fan throughout the night

If it is possible, I recommend running the whole house fan throughout the night in summer. As the outdoor temperature will stay cool enough throughout the night, the fan will keep the house cool without air conditioning.

Step 8: Turn off the whole house fan before it is hot outdoors

The worst thing you can do with a whole house fan is to run it when the outside temperature is higher than that is inside the house. This will bring hot air from the outdoors and make the house hotter. Whole house fans should be switched off when it is getting hot, preferably just after the mornings. The best thing to cool a house in this situation is to use your air conditioner.

How many windows should I open to run a whole house fan?

When running a whole house fan, it is important to keep your windows open to allow air intake from outdoors. But one question that comes to our minds is how many windows do I need to open?

It is recommended to partially open two or three windows when running a whole house fan. The point is to create a smooth breeze flowing throughout the house. If the house is big, more windows may need to be opened to ensure sufficient airflow.

The larger the house, the more will be the CFM of the fan, and maybe you need to open more windows. There are no clear guidelines on how many windows need to be open, as this is usually found out by trial and error. Opening too many windows will spread out the air circulation, and hence that is not recommended. Opening just enough windows will create a cool breeze throughout the house, and this is the most recommended setting. So do some trial and error and find out how many windows you want to keep open.

Also, opening the windows opposite to the sun and those which are far away from the location of the fan will help to draw cooler air and to circulate it through more areas of the house.

Do all windows need to be open for the whole house fan?

It is recommended not to open all windows when running the whole house fan. If all windows are open, the fan will pull more air through the nearby window, leaving no airflow through other windows. This will create hot pockets in the house. To avoid this, open only a few windows far away from the fan. This will ensure air circulation throughout the house, thus eliminating the formation of any hot pockets.

A diagram showing how a whole house fan works.
Working of a whole house fan

How long should I run a whole house fan?

It is common to wonder how long one should run their whole house fan. This is often the case when you are using the fan for the first time.

How long you run a whole house fan is entirely your personal preference. It is recommended to run the whole house fan as long as the outdoor temperature is cooler than that indoors. Many companies recommend running them throughout the night to keep the house consistently cool, so in the morning, the air conditioner will have an easy job keeping the house cool.

What is the best time to run a whole house fan?

As mentioned above, whole house fans can be run whenever the outside temperature is lower than that is inside. So what are the best times to run them?

The best times to run a whole house fan are evenings, nights, and early mornings. These are the usual times when the outside temperature remains lower than that inside. These times depend on the climate you live in. My recommendation is to run the fan whenever outdoors are cooler.

How to run a whole house fan in a two-story house?

Many houses are two-storied. How will you run a whole house fan in such a house? Worry not, the steps are the same as running one in a one-story house. Here are they;

  1. Turn off your AC
  2. Close the attic door as well as the fire dampers.
  3. Partially open two windows on the ground floor and one window on the first floor.
  4. Turn on the whole house fan and run it until it is hotter outdoors

The steps are exactly the same however in this case, you need to open a window on the top floor as well. The air will also come through the windows on the ground floor, blowing through the stairs into the first floor and into the attic. You can limit this circulation by opening more windows on the first floor. Also in a two-story house, the ground floor will remain relatively cooler, it is the upper floor that usually needs cooling. In most cases, the whole house fans will be installed above the stairs. Therefore, proper cooling of the first floor is possible only if the windows on that floor are open.

What will happen if a whole house fan is run with windows closed

Do not run a whole house fan with the windows and doors closed. Whole house fans are powerful fans, and they pull air with a great deal of force. Therefore, there should be sufficient make up air supply for the fans to work properly.

If windows and doors are closed while running the whole house fan, the fan will create a negative pressure inside the house so high that air will be sucked through all possible outlets like your chimney, furnace, and HVAC. This will cause the back-drafting of lethal gases that are supposed to be vented out.

You definitely do not need anything of the sort. Keeping a few windows open will avoid all these hazards.

How long does it take to cool a house

It will take only as low as ten minutes for a whole house fan to cool a house. A fan with a high airflow rating will cool a house faster.

Whole house fans have high air flow rates, and many will be able to do a complete air change in a minute or two. Therefore, if the outside air is cool, the house will be cooled within a few minutes.

What speed settings should I use?

Some whole house fans come with multiple speed settings. You can use whichever speed setting you feel is right for you. However, I recommend starting the fan at its highest speed to quickly cool the house and then switching to a lower speed to save energy.

Can I run the whole house fan with the AC on?

I have seen a lot of people asking whether they can use their whole house fan while running the air conditioning!

Do not run the whole house fan with the AC on. The fan will vent every bit of conditioned air from the house. This will also add extra load to the air conditioner.

To be honest, nothing good will come out of this combination.

How to use a whole house fan in the winter

Do not use whole house fans in the winter season. These fans are made to be used in the summer. During winter, the whole house fans should be winterized to prevent any heat loss from the house.

Further reading:

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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