Whole House Fans & Ventilation

Cool air is drawn in through windows and circulated up into the attic space and out through the roof vents.A relatively new concept, whole house fans and ventilation systems are rapidly gaining in popularity thanks to rising fuel costs and increased interest in conserving energy resources.

Gone are the days when new home builders simply slapped up a couple of gable vents to circulate a bit of air on stifling hot days; in a home without adequate attic and “dead space” ventilation, these areas can get up to 150 degrees Fahrenheit, making it a challenge to keep inside room temperatures cool enough to be comfortable!

Today, we better understand and appreciate the need for adequate ventilation in the home. Read on to learn ways you can more efficiently cool your home and save money on central air conditioning costs by installing a whole house fan.

The Concept behind Whole House Ventilation

In a home designed to leverage physics to keep things cool inside, a whole house fan pulls air in through open windows and vents it up through the attic and roof, increasing air circulation throughout the entire structure. An efficient whole house fan changes the air inside between 30 and 60 times an hour, depending on the climate, home floor plan and other factors.

Whole house fans can be added to an existing home in most cases, but today many people choose to design their home with the concept of whole house cooling in mind; if you live in a location with temperate weather, such as a coastal area, you may even be able to design your home without any central air conditioning system.

Whole House Cooling Fan Benefits

The whole house fan and louvers before installation.Simple and inexpensive to operate, a whole house fan draws cool air from outside into the home, creating good air flow, and exhausts warmer air upward to the attic and dead spaces over the living space, where it finally exhausts back outside. The benefits include improved ventilation throughout the entire home, cooler temperatures inside the living space and better evaporative cooling.

When temperatures outside are over 80 but under 100, this can keep the inside of your home cool enough that air conditioning may not even be needed! Whole house cooling benefits include:

  • Low cost of equipment and installation:
    • Cost of whole house fan = $150 to $350
    • Cost of window air conditioning unit = $250 to $750
    • Cost of central air conditioning system = $2,000 to $5,000
  • Improved ventilation, resulting in lower cost to cool your home.
  • May suffice as primary or only cooling system in a home.
  • Keeps indoor temperatures more constant since whole fan runs continuously during warm weather, whereas central air conditioning systems periodically turn on and off to keep inside temperature within a threshold.

How to Size a Whole House Fan

Cubic Feet per Minute (CFM) is the measurement used to determine the size and power needed when installing a whole house fan. To calculate the correct dimensions and specifications:

  1. Calculate your home’s total volume in cubic feet by multiplying the square footage by the floor to ceiling height.
  2. Multiply the volume by 30 or 60 air changes per hour, depending on the power of the unit you are installing.
  3. Divide that number by 60 minutes to determine the CFM your whole house fan will need to produce in order to cool your home.

Equation: (Square footage) x (Floor-to-Ceiling Height in Feet) x (30 or 60) / (60) = (Required CFM)

Disadvantages of Installing a Whole House Fan

The three main drawbacks to a whole house fan are temperature, humidity and dust. Since a whole house fan is simply drawing air in from outside and circulating it through your home, it can only cool the home to the outside temperature or slightly less if you count the air flow. If you live in an area that regularly gets summertime temperatures above 90 degrees F, you will probably still be using the air conditioning regularly!

Louvers open and close to seal up the attic space when the whole house fan is not in use.Since a whole house fan is drawing outside air in through open windows and/or doors, there is no real air filtration; humidity, pollen, dust and other particulates are flowing into your home whenever the fan is turned on. This is the biggest downside and one that causes many people to hesitate when considering installing a whole house fan.

Some people believe that circulating fresh air from outdoors is healthier than being cooped up all day inside an airtight home with the A/C running. On the other side of the debate, some people believe that it is best to try and keep as much dust, pollen, etc. as possible out of the home by using the central HVAC system’s filtration. Only you can decide what is best for your home and family!

The other disadvantage is noise; a high power whole house fan can be noisy. Better units run at lower speeds and have more fan blades in order to circulate as much air as possible without producing as much sound as a faster fan speed does. The higher quality whole house fans are also multi-speed.

Rubber or felt gaskets should also be used when mounting the fan to help reduce vibration and noise; most units are designed with this in mind.

Using Ductwork for Whole House Cooling

Some people have modified the central air conditioning system in their home to act as a whole house ventilation system. While this may seem like a good option, it can be trickier than it seems and is not generally recommended.

The basic modification required involves installing a damper to control air flowing from the living space into the attic space and an intake duct in the attic-space to pull air into the system. You should definitely consult with an expert before considering this type of modification to your central air conditioning system.

Attic Fans Vs. Whole House Fans

Attic fans help circulate and exhaust warm air in the attic space only and have no direct impact on the temperature inside the living space; although an attic space that becomes overly hot doesn’t help things and indirectly keeps things warmer. Whole house fans, on the other hand, actually vent air from inside the living space up into the attic space; so while the attic fan and the whole house fan work together to pull air through your home and exhaust it up through the roof vents, they can not be directly compared as home cooling or ventilation systems, since each has a separate purpose.

Installing and Using a Whole House Fan

  • For the seasoned do-it-yourselfer, installing a whole house fan will be a challenging project, but consulting an expert will help ensure that all aspects of installation are correct, including fan size and displacement, attic and roof ventilation, electrical circuits and wiring, etc.
  • In most cases, attic ventilation will need to be addressed; with all that air coming up from inside the home, you need to be sure that it exhausts adequately from the attic space(s), which means between 2 and 4 times the normal attic area venting or one square foot per each 750 CFM the whole house fan produces. The more freely the attic space is vented, the more efficiently the whole house fan will be able to operate.
  • Most units come with a louvered cover that opens when in use and closes when the fan is off; be sure you can seal the opening well during the winter months to prevent warm air from your furnace or other home heating system from escaping! This is also important if you do run the air conditioning system during the summer; you don’t want to run the A/C at the same time you are operating the whole house fan or you’ll just be exhausting the cool air and wasting money!
  • Be sure to open all windows and doors that are screened when you operate the whole house fan; without adequate ventilation, the fan may cause a back draft in the furnace or gas-operated appliances such as a water heater or clothes dryer; you don’t want carbon monoxide or other combustion gases circulating indoors!
  • A whole house fan should be installed in the most central place in the house possible so that air is drawn from all rooms into the attic space.
  • The whole house fans should be installed with an automatic shutoff mechanism that trips in the event of a fire.

Whole House Cooling Tips

  • Generally speaking, you should not operate a whole house fan when outside temperatures are above about 85 degreed F; this can actually make it hotter inside the house than turning the system off.
  • Run the whole house fan in the evening and early morning hours when the air temperatures outside are cooler than the inside temperature, turning it off and closing up the house during the hottest part of the day when circulating air would only cause the indoor temperature to rise.
  • If needed, switch the whole house fan off during the hottest part of the day, close all the windows and doors and run your central air conditioning until the outside temperature is below 85 degrees; then open up the house and turn the whole house fan on to avoid having to use the A/C any more than necessary.
  • Control circulation and air flow by opening windows in occupied rooms and leaving a few windows in unused rooms closed; this will produce better air flow and cooler temperatures in the rooms you use the most.
  • A whole house fan works best in a well-insulated and tightly sealed home, allowing it to heat very slowly during middle of the day; by the time it begins to get warm enough to feel uncomfortable, the hottest part of the day should have passed and you can use the whole house fan to cool things down again.
  • Be sure to install screens on all operable windows and doors if possible; the more you can open up the house, the more air the whole house fan will be able to circulate and cool the living space.

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