Under certain circumstances, a whole house exhaust fan and timer can lower the temperature of your house without air conditioning.
The Goal: Lower the house temperature without using whole house air conditioning
An alternative to whole house air conditioning is to use an exhaust fan. The idea is to pull the hot air out of the house and thereby pull cooler air in through open windows.
The overall concept: Exhausting air will create a slightly lower pressure that will draw outside air in. If the outside air is cooler, then you will cool the house down.
Things you need:
While it may sound obvious, you need outside air that is cooler than the inside air. This usually means running the fan at night or after a thunderstorm.
You will also need a fan. You can go with a window fan or an in-ceiling fan that exhausts through your roof or roof vents. A window fan is by far the less expensive option. A whole house built in fan will probably require electrical work and possibly adding vents in the roof. It will, in some cases, require a building permit and inspection. For this article, we will discuss a window fan.
If you go with a window fan, you should look for a window and with the following characteristics:
- An unused room is probably the best alternative such as a guestroom. You need a room where the door is open all the time.
- A window that faces a direction that minimizes the possibility of rain intrusion. My fan is in a window facing north. That side of the house does not get driving rain in most cases. An overhanging roof or awning would be great.
- You should be able to leave the window open for most of the summer. Running the fan with the window closed could burn the fan out and possibly cause a fire.
- Ideally, the window should be on the top floor as heat rises.
- The fan should be relatively quiet. However, you need to consider the cubic feet per minute that it can move.
Other circumstances and considerations
Because of my lifestyle, the fan works well. I use room air conditioners for my office and the bedrooms.
You need to leave the screen in the window to prevent bugs and nasty bugs such as wasps from entering when the fan is off. The screen should be cleaned once a year or whenever it starts to get a build up of dust.
A timer is important.
I use a WEMO wifi smart plug. The fan is set to go on at 8pm and shut off at 10 am. If I am away from the house and the temperature drops I can turn the fan on remotely. If I am away and there is a bad rainstorm, I can turn the fan on. The outgoing air current will keep the worst of the rain from coming in. Some higher end
Unfortunately there does not seem to be wifi controlled fans on the market at this time. That will probably change over time.
The image below is the dashboard for my WEMO devices. With the WEMO, I can set a timer and associate that timer with a particular device.
The basic plan:
Set the timer to turn the fan on in the evening and shut it down in the morning. You open windows on a far side of the house. You don’t want to do something like fully open a bathroom window next door to the fan. That will simply pull the air through a short distance. That will not conserve energy and will defeat the concept.
Relative humidity will also determine the effectiveness of a whole house fan.
Pros
If you don’t need to cool an entire house, this should prove to be a much more economical solution. A fan motor draws far less energy than even an energy efficient air conditioner or heat pump.
Some areas are taking control of thermostats and limiting your temperature settings. I’ve seen reports of homeowner’s thermostats being set to absurdly high levels. A whole house fan might give you an alternative in those situations.
Cons
In some cases, you can draw gnats in through the windows. You don’t want windows open with a light nearby as that will attract insects. Also, if a skunk lets one rip at night it will draw the stink right in. When the lawn guys come, I shut the fan down as it will draw the dust and pollen in.
You will bring in dust and pollen. If you suffer with allergies, this is probably not a good solution for you
If you are trying to cool a bedroom at night, you will need to leave the bedroom door open.
The cooling effect depends on the temperature difference between the inside air and the outside air. Humidity will also factor in. One thing to keep in mind is that everything in the house soaks up heat. If you go to bed with an inside temperature of 80 degrees and an overnight low of 70 degrees, you might see an indoor temperature of about 76 by the morning.
WARNINGS – The concept of a forced draft COULD cause any fires to spread more quickly than normal. CONSIDER THIS CAREFULLY. If you go with a whole house fan, you should check any building codes.
CONSIDER THE POSSIBILITY OF RAIN SOAKING THE FAN. Every installation will be different. It goes without saying that electricity and water are usually a bad combination
Summary
I’ve used this concept in Southeastern Pennsylvania for a couple of decades. For the most part it works well and saves a LOT of money. This is even more true with skyrocketing utility prices.