Choosing The Best Exhaust Fan System
Bathroom And Kitchen Exhaust Fans
Choosing the best exhaust fan system is an important part of your home’s ventilation system. They remove moisture and odor from your house, improving indoor air quality.
The most important factor in a bathroom or kitchen fan is its ability to remove moisture, thus decreasing humidity in your house. High humidity damages wall and structure materials as well as causes the growth of mold. Mold can negatively affect your health. Moisture and stale air that carry contaminants and pathogens inside your home should be removed, mechanical ventilation can improve the quality of your indoor air.
Fan and Exhaust Systems
The two most common types of fans are impeller fans and blower fans.
Impeller fans: This type of fan moves air with turning blades. I don’t see these types of fans too much anymore.
Blower fans: Are wheels with small fins. They are often called squirrel cages and are better capable of moving air than impeller fans. Most exhaust systems consist of the exhaust fan, duct work or piping and an exterior exhaust vent hood.
Bath fan systems are usually installed in the ceiling near the source of moisture. The fan is at the ceiling level and duct work exhausts the moist air out of the house. Kitchen exhaust systems usually have the fan and fan motor in the exhaust hood. Other systems use an in-line fan, which is in the exhaust duct, or a fan outside the house. In-line and outdoor exhaust fans are usually quieter than systems with the fan in the room.
Steps In Choosing The Best Exhaust Fan System:
First, choose the quietest, most energy-efficient fan that will accomplish what you need. Most fan labels have Home Ventilating Institute (HVI) ratings so you can compare noise and energy efficiency.
Exhaust fans measure noise in sones. Quiet fans have a 1.5 sone rating. Standard fans are around 4 to 6 sones.
Determining Your Rooms Cubic Feet Per Minute [CFM’s]:
Before you can choose this fan you will need to size your new fans CFMs to your room.
Finding a fan that will be efficient and handle the size room you have is important. To do this you need to determine the Cubic Feet Per Minute [CFM] of the room and buy a fan to match that. Multiply the rooms width x Length x height x 0.13 to determine the rooms minimum CFMs. [W x L x H x 0.13 – minimum CFM.
Determine Air Exchange Per Hour [ACH’s]:
Where you intend to install the exhaust fan will have a direct bearing on its size. As per the Home Ventilating Institute (HVI), different locations in your home require varying Air Changes Per Hour (ACH) in order to be ventilated properly.
Here are the ACH requirements recommended by HVI.
- 8 ACH for bathrooms
- 15 ACH for kitchens
- 6 ACH for rooms other than bath and kitchen
ACH refers to the number of times the air should be completely changed in an hour. Thus, an 8 ACH recommendation for bathrooms means the exhaust fan should have the capacity to completely change the air in the bathroom 8 times in one hour.
To determine your ACH rating multiply your CFM’s x [recommended ACH for the room your exhausting.]
Sizing Kitchen Exhaust Fans:
When sizing an exhaust fan for the kitchen, you have to take into account the location of your kitchen cooking range or the size and location of the range hood if there is one. Here are the recommended CFM ratings for kitchen range hood exhaust fans
A rule of thumb is for every 10,000 BTU of the range, it is recommended a minimum of 100 CFM. So if your range is rated at 50,000 btu’s, you would consider getting a fan with at least 500 CFM.
Look for a fan with replaceable parts and permanent lubrication. A fan suitable for continuous use is always preferable and means durable, quality parts were used. Be prepared to pay more for a quality fan.
Determining Fan Duct Length:
Ducting can affect fan performance. Uninsulated, undersized, or droopy flex ducting, ineffective or dirty backdraft dampers and exhaust louvers can cut rated airflow by more than 50 per cent.
Solid smooth aluminum duct work is the best but not the easiest to install. Solid duct has a better airflow due to its low-resistance (smooth) exhaust ducting.
Second to solid duct would be the flexible aluminum. Seal the joints and insulate sections that run through unheated spaces. Follow the manufacturer’s specifications for installing the ductwork.
All fans come with instructions that instruct you how far a run your duct work can be. Try to layout your installation with minimal turns and avoid dips where moist air can condense and accumulate, causing pooling. One thing that people do not realize is that for every ninety degree elbow or turn is like adding 15 feet of ductwork in air flow resistance. Try to minimize these in your installation.
Choose a location for your exhaust hood where it will not cause moisture damage on exterior surfaces. Inside the house sofit is NOT a proper place for an exhaust vent expelling moist air.
The static pressure in any duct run differs according to the material of the duct, number of elbows and turns, exterior wall cap and wall jacks etc. Listed below are the standard values for different duct components.
Smooth metal duct:
- Actual duct length x 1
Flex aluminum duct:
- Actual duct length x 1.25 (for 4”diameter duct)
- Actual duct length x 1.50 (for 6”diameter duct)
Insulated flex duct:
- Actual duct length x 1.50 (for 4”diameter duct)
- Actual duct length x 2.00 (for 6”diameter duct)
Wall caps and roof caps:
- 30 feet for each cap (for 4”diameter duct)
- 40 feet for each cap (for 6”diameter duct)
Elbows and turns:
- 15 feet for each (for 4”diameter duct)
- 20 feet for each (for 6”diameter duct)
Install a timer switch and make sure you use it. Timer switches can be left on after you’re done and will ensure that the fan has time to work by exhausting the room or moist air
A timer switch allow you to specify operating times or maximum humidity levels are preferable to those where the operation is pre-set by the manufacturer. Use a delayed fan shut-off to keep the fan running for 15-20 minutes after you leave the room.