The importance of exhaust fans in ventilation and ensuring indoor air in certain parts of our homes and buildings is fresh, breathable and healthy cannot be overemphasized.
In rooms like bathrooms, kitchens, garages and other sensitive parts of the house, the type of air control measures you apply can determine if those places will smell fresh, have the right amount of humidity, or even the condition of the walls.
Hence, homeowners are required and advised by bodies and regulatory codes like the International Residential Codes and the Environmental Protection Agency to ensure the installation of ventilation systems such as exhaust fans.
In shopping for an exhaust fan, one boggling consideration is in sizing the appliance in relation to the room you intend to place it.
The type of room, its size, the components in the room, and the nature and frequency of activities that happen there are some of the factors that determine the capacity of fans you put in there.
This begs the question, “how many exhaust fans do you need?”. What determines the number of fans you should use? These are some of the many questions we’ll answer in this post.
How Many Exhaust Fans Do I Need?
This is a really broad question and it largely depends on a number of factors, including the type of room that needs the exhaust fans, the size of the room, the items in the room, and even the room’s access to the outside wall and availability of windows.
Let’s consider these factors.
1. Type of room
The type of room in the building determines whether or not an exhaust fan is required. Exhaust fans are most commonly applied in spaces that are prone to humidity buildup, mold growth, damp air, and even bad smells and odors.
For instance, a bathroom with a shower and jetted bath may need more than one exhaust fan. In the same vein, a kitchen may require more than one exhaust fan, while a basic powder or toilet room would make do with a single one (if required).
2. Size of room
This is the most common way to determine how many exhaust fans you’d need. You need to calculate the size of the room to know what size exhaust fan should go in there.
For a space (bathroom, kitchen, garage, etc) that is less than 100 square feet, the rule of thumb is to have 1 CFM of exhaust per square foot.
However, for rooms more than 100 square feet, you need to add up the CFM requirement for each component, such as shower, toilet, jetted tub, sink, etc to get the total CFM requirement.
Where your single unit is below par, the wise thing to do would be to have an additional unit to make up for the deficiency.
For instance, if you’ve just moved into a new house with a larger bathroom and realized that your 76 CFM exhaust fan is too small for it, you can sum up the CFM requirements of the items in the new bathroom and get an extra exhaust fan to measure up.
3. Items in the room
This has already been mentioned earlier but it’s important to emphasize that when you have a bathroom that’s bigger than 100 square feet, the items you have in there will become the determining factors for how much exhaust is required.
A bathroom with just a shower, toilet and sink is certainly not the same as a bathroom with a jetted tub, hot tub, shower, sink and toilet. The latter may require more than one exhaust fan if the existing fan isn’t strong enough.
4. Access to outside wall/window availability
Some bathrooms, hot tub rooms, kitchens, etc are located in parts of the house where there is no access to outside walls. This means no windows or direct venting systems.
Where a single exhaust fan may be enough for a kitchen or bathroom with a window, it may not be enough for one without a window. This is because the contribution of the window to ventilation is absent in a closed-off room without one.
At the end of the day, it is the capacity of the exhaust fan (as measured in CFM) in relation to the size of the room that determines if a second one is required or not.
How Many Exhaust Fans Do You Need in A Bathroom?
Deciding on exhaust fans for your bathroom is more a factor of CFM rating than the number of units. If you find one exhaust fan that meets the CFM needs of your bathroom, you should go for it.
The only time you may need to have more than one fan is when the existing one is lacking in sufficient CFM capacity.
Also, it’s possible you’re in love with a particular product with a less-than-required CFM rating, you may need to have multiple of that unit to measure up. The goal is to achieve 1 CFM per square foot. So, a measurement of your bathroom is important.
If you have a 10 x 8 bathroom, for instance, that’s an 80 square foot bathroom and you’d need an exhaust fan with a rating of 80 CFM or slightly higher.
However, if the bathroom measures more than 100 square feet, then you need to add up all items/fixtures in the bathroom with regards to their CFM requirement.
CFM requirement for each fixture
- Jetted tub 100 CFM
- Toilet 50 CFM
- Shower 50 CFM
- Bathtub 50 CFM
If your bathroom is larger than 100 square feet and contains all four of the above fixtures, it means you require an exhaust fan with a rating of not less than 250 CFM.
Where a single unit of your choice with the rated CFM is not available, you can select two smaller units for the bathroom. A master bathroom, for instance, is usually larger than a regular full bathroom.
In the U.S., an average-sized primary bathroom ranges from 115 to 210 square feet. On the other hand, a full bathroom is usually sized at 5×8 feet, which equals 40 square feet.
This shows a huge disparity between the two types of bathrooms, and it won’t be out of place to see a primary bathroom using two exhaust fans of around 120-180 CFM each.
A full bathroom, on the other hand, would generally make do with a single unit rated 50 CFM and above.
How Many Exhaust Fans Do You Need in A Kitchen?
There is no residential code that requires you to have an exhaust fan in a kitchen. However, it is not uncommon to find large and industrial kitchens with one or two exhaust fans.
Due to the amount of cooking and the frequency of activities there, you’re bound to have floating moisture in the air, cooking smells, and grease which would need constant venting.
However, unless you have a steamer that’s constantly running or you run the kitchen for more than 12-16 hours daily, one exhaust fan should do.
You may only need more than one exhaust fan if the kitchen doesn’t have a window that opens. In this case, running two exhaust fans to the ceiling and out of the house should be a good way to go.
Also, kitchens are quite large. In the U.S., an average residential kitchen is about 160-250 square feet. That’s 103 square feet in homes smaller than 1,500 square feet, and 238 square feet in homes 4,000 square feet and beyond.
The size should also be a factor in deciding how many exhaust fans you should install, if at all necessary.
How Many Exhaust Fans Do You Need for A Garage?
A garage is another very crucial part of the house where exhaust fans are required. Depending on the type and size of the garage, the air exchanges required ranges from about 6 per hour to almost 30 per hour.
This will also determine how many exhaust fans you’ll need to install. As a rule of thumb, a residential garage used as a regular park or storage area would require 800 CFM for every 1,000 square feet.
On the other hand, workshop garages would need around 4,000 CFM for the same 1,000 square feet. So, depending on the size and usage of your garage, you’d be able to calculate how many exhaust fans would do.
Garages, especially those in frequent use, can heat up a lot because of their location and enclosed nature. This is one of the reasons exhaust fans a needed; to remove warm air and odor.
If you find a good and powerful exhaust fan with the required rated CFM, you can install that one unit. However, if you need more than one, do not hesitate to install multiple units, especially in the workshop and industrial garages.
It’s impossible to say how many exhaust fans are needed in a bathroom, kitchen or garage without first considering the size of the room, the fixtures of that room and the number of activities carried out in there.
Also, you should only consider using two or more exhaust fans if the one you already have or are planning to buy falls short of CFM requirements.
Whatever the case, be sure to follow stipulated rules and this guide will also provide a blueprint for you in the very tough decision of sizing your exhaust fan and knowing whether to use one or more than one.