Find your best fan from our range of cooling fans

Geometrically similar fans can be characterized by the following four equations:

Volumetric Flowrate: G = KqND3

Mass Flow Rate: m· =Km ND3

Pressure: P = KpN2D2

Power: HP = KHPN3D5

where:

K = constant for geometrically and dynamically similar operation
G = volumetric flow rate m· = mass flow rate
N = fan speed in RPM D = fan diameter
HP = power output = air density

From these relationships, it is possible to calculate a fan performance at a second condition. Table 1 is a summary of the fan law equations in a form useful for fan analysis.

Cabinet Cooling Hints
In addition to selecting a fan, there may be some choice in the location of the fan or fans, and in this regard, the illustration in Figure 4 may prove useful. The following comments should also be kept in mind with regard to fan location:

Whole-House Fans
A whole-house fan can substitute for an air conditioner most of the year in most climates. Whole-house fans combined with ceiling fans and portable fans provide acceptable summer comfort for many families, even in hot weather.

How Whole-House Fans Work
The whole-house fan pulls air in from open windows and exhausts it through the attic and roof. It provides good attic ventilation in addition to whole-house ventilation.

You can regulate cooling by simply closing windows in the unoccupied areas and opening windows wide in occupied areas. Many people cool the bedrooms at night and the living areas during the daytime. Whole-house fans should provide houses with 30 to 60 air changes per hour (varies with climate, floor plan, etc.—check with a professional to determine what is appropriate for your home). The air-change rate you will choose depends on your climate and how much you will depend on the whole-house fan for cooling.

Cooler, shadier areas don't require as much ventilation as warmer, sunnier ones. Houses entirely dependent on whole-house fans require a bigger fan because there is no air conditioning to fall back on.

Sizing a Whole-House Fan
Whole-house fans are sized in cubic feet per minute (cfm) of ventilating power. To determine the size you'll need, first calculate the volume of your house in cubic feet. To do that, multiply the square footage of the floor area you want to cool by the height from floor to ceiling. Take that volume and multiply by 30 to 60 air changes per hour (depending on the power you need). Then, divide by 60 minutes to get the cubic feet per minute of capacity your house requires. [(Square feet______ x room height______) x 30 or 60/ 60 = cfm required _________. ]

Installing and Using a Whole-House Fan
Installing a whole-house fan is tricky and should be done by a professional. Attic measurements, dedicated circuit wiring, and possibly new attic vent installation should be performed by an experienced person.

Attic ventilation must be increased to exhaust the fan's air outdoors. You'll need 2 to 4 times the normal area of attic vents, or about one square foot of net free area for every 750 cfm of fan capacity. The net free area of a vent takes into account the resistance offered by its louvers and insect screens. More vent area is better for optimal whole-house fan performance.

Some fans come with a tight-sealing winter cover (or you can build one). If you switch between air conditioning and cooling with a whole-house fan as the summer weather changes, build a tightly sealed, hinged door for the fan opening that is easy to open and close when switching cooling methods.

Drawbacks of Whole-House Fans
Whole-house fans can be noisy, especially if improperly installed. In general, a large-capacity fan running at low speed makes less noise than a small fan operating at high speed. All whole-house fans should be installed with rubber or felt gaskets to dampen noise. You can set a multispeed fan to a lower speed when noise is a problem.

Evaporative Coolers
Evaporative coolers or swamp coolers are a popular and energy-efficient cooling strategy in dry climates of the United States.

Hot outside air enters the swamp cooler. The air passes over water-saturated pads, and the water evaporates into the air. The energy used removes heat from the air. The 15- to 40-degree-cooler air is then directed into the home, and pushes warmer air out through windows.

Because this process also humidifies the air, swamp coolers are best used in areas with low summertime relative humidity.

Evaporative coolers use less than one-third the energy of air conditioners, and cost about half as much to install. Unlike central air conditioning systems that recirculate the same air, evaporative coolers provide a steady stream of fresh air into the house.

Sizing and Selection
Evaporative coolers are rated by the cfm of air that they deliver to the house. Most models range from 3,000 to 25,000 cfm. Manufacturers recommend providing enough air-moving capacity for 20 to 40 air changes per hour, depending on climate.

Installation
Evaporative coolers are installed in one of two ways: the cooler blows air into a central location, or the cooler connects to ductwork, which distributes the air to different rooms. Central-location installations work well for compact houses that are open from room to room. Ducted systems are required for larger houses with hallways and multiple bedrooms.

Most people install down-flow evaporative coolers on the roofs of their houses. However, many experts prefer to install ground-mounted horizontal units, which feature easier maintenance and less risk of roof leaks.

Small horizontal-flow coolers are installed in windows to cool a room or section of a home. These portable evaporative coolers work well in moderate climates, but may not be able to cool a room adequately in hot climates. Room evaporative coolers are becoming more popular in areas of the western United States with milder summer weather. They can reduce the temperature in a single room by 5 to 15 degrees.

Operation
An evaporative cooler should have at least two speeds and a vent-only option. During vent-only operation, the water pump does not operate and the outdoor air is not humidified. This lets you use the evaporative cooler as a whole-house fan during mild weather.

Control the cooler's air movement through the house by adjusting window openings. Open the windows or vents on the leeward side of the house to provide 1 to 2 square feet of opening for each 1,000 cfm of cooling capacity. Experiment to find the right windows to open and the correct amount to open them. If the windows are open too far, hot air will enter. If the windows are not open far enough, humidity will build up in the home.

You can regulate both temperature and humidity by opening windows in the areas you want to cool, and closing windows in unoccupied areas. Where open windows create a security issue, install up-ducts in the ceiling. Up-ducts open to exhaust warm air as cooler air comes in from the evaporative cooler. Evaporative coolers installed with up-ducts will need additional attic ventilation.

Filters remove most of the dust from incoming air—an attractive option for homeowners concerned about allergies. Filters can also reduce the tendency of some coolers to pull water droplets from the pads into the blades of the fan. Most evaporative coolers do not have air filters as original equipment, but they can be fitted to the cooler during or after installation.

Evaporative Cooler Maintenance
Save yourself a lot of work and money by draining and cleaning your evaporative cooler regularly. Build-up of sediment and minerals should be regularly removed. Coolers need a major cleaning every season, and may need routine maintenance several times during the cooling season.

The more a cooler runs, the more maintenance it will need. In hot climates where the cooler operates much of the time, look at the pads, filters, reservoir, and pump at least once a month. Replace the pads at least twice during the cooling season, or as often as once a month during continuous operation.

Some paper and synthetic cooler pads can be cleaned with soap and water or a weak acid according to manufacturer's instructions. Filters should be cleaned when the pads are changed or cleaned. Caution: Be sure to disconnect the electricity to the unit before servicing it.

Two-Stage Evaporative Coolers
Two-stage evaporative coolers are newer and even more efficient. They use a pre-cooler, more effective pads, and more efficient motors. They don't add as much humidity to the home as single-stage evaporative coolers, but are still much more efficient than air conditioners.

Drawbacks of Evaporative Coolers
Evaporative coolers should not be used in humid climates because they add humidity. Also, they cool your house down to a higher temperature than an air conditioner would.

They require maintenance (albeit easy) about once a month. If the cooler is installed on the roof, there is some roof deterioration caused by routine maintenance trips. A sunlit rooftop cooler will be about 1 degree Fahrenheit less effective than a shaded cooler. Rooftop maintenance also requires using a ladder, which may be an inconvenience.