How many CFM do I need for a 5x8 bathroom?

Author: Jada Mann  |  Last update: Friday, June 13, 2025

A standard 5 x 8 bathroom needs a good-quality fan that draws a minimum of 50 cfm. Larger master baths may require stronger fans to efficiently pull the humid air from the room.

How many CFM for a 5x8 bathroom?

The Home Ventilating Institute recommends a minimum 1 CFM per sq foot in bathrooms smaller than 100 sq ft. That will give you the minimum 8 air changes per hour in a bathroom with standard 8' ceilings with a 50CFM minimum.

Is 110 CFM too much for a small bathroom?

If it's just a small bathroom with a toilet and a shower, you may only need a 100 CFM fan. If you have a jetted tub and shower, you will likely need a 200 CFM fan. CFM is a measure of the fan's ability to move air.

How many CFM do I need for an 8x8 bathroom?

Bathroom vent fans are rated for the amount of air they can move, measured in cubic feet per minute, or CFM. Standard fan sizing applies to bathrooms that are 100 square feet or less. The rule of thumb is that you need at least 1 CFM per square foot of room area.

What is a good CFM for a small bathroom?

A rule of thumb is 1 cfm per square foot of bathroom. You don't need to include the closet. Another recommendation is 8 air changes per hour, or cubic foot of room divided by 7.5, which is usually a little more than 1 cfm per square foot. The separate toilet room needs its own fan. The minimum size is 50 cfm.

Calculating the CFM Needed in a Bathroom | Fan Fact Friday

What happens if bathroom fan CFM is too high?

This can cause warped cabinetry, foggy mirrors, and mould or mildew growth. A fan that is too big can cause a bathroom to be cold and noisy. This is why calculating the correct CFM is important.

Is 80 CFM enough for small bathroom?

Choose a fan that can ventilate at least 1 CFM per square foot of room. So, for an 80 square foot bathroom, select an 80 CFM fan. For bathrooms 50 square feet and smaller, it's recommended you purchase a bath fan designed for small rooms. In other words, choose under 79 CFM bath fans.

Is 70 CFM enough for a bathroom?

We recommend at least an 80 CFM for most bathrooms but a 100/110 for a larger master bathroom. This will help move the moisture out of the bathroom and reduce the risk of mold.

How many CFM do I need for a 10x10 room?

How many CFM do I need for a 10x10 room? It is considered that 135 CFM is needed per square foot of space. So 13.5 CFM would be required for a 100-square-foot area. A room of 1,000 square feet would require 135 CFM.

What is code for venting a bathroom fan?

To fulfill the local exhaust airflow requirements of ASHRAE 62.2 (2010) and the International Residential Code (IRC 2021, Section M1507), bathroom fans should have a mechanical exhaust capacity of ≥ 50 cfm for intermittent operation or ≥ 20 cfm of ventilation when operated continuously.

How do you ventilate a small bathroom?

Air needs to circulate to prevent excess moisture from building up, and there are certain steps you can take to help keep it moving.
  1. Install an extractor fan. ...
  2. Keep windows open during and after showering. ...
  3. Keep your shower door open after showering. ...
  4. Wipe down surfaces. ...
  5. Install bacteria-reducing wall panels.

Is 5x8 big enough for a bathroom?

A: Yes, a 5×8 bathroom layout can accommodate a full bathroom, including a toilet, sink, and either a shower or a shower-tub combo. These components can fit comfortably within the space.

How many CFM do I really need?

Performance: The higher the CFM, the more powerful the range hood is at removing smoke, steam, and odors. A good range hood CFM depends on the size of your kitchen, the type of stove, and how frequently and intensely you cook. Generally, for every foot of your range's width, you need 100 CFM.

How many square feet is a 5x8 bathroom?

A 5x8 bathroom is the most common bathroom floor plan that can include all of the necessary elements—a bathtub or shower, sink, and toilet. It's not spacious, but it's enough room for everything you need. How many square feet is a 5x8 bathroom? A 5x8 bathroom is 40 square feet.

Can I have too much CFM in my bathroom?

Not only will this exhaust fan be drawing more energy than necessary, but the extra CFM might cause other issues like drafts or the inability to dry up the moisture still hanging around in the bathroom.

How do I calculate how many CFM I need?

You can calculate the CFM needed for your system. Start with the total volume of air (in cubic feet). Divide by the exchange rate (how quickly you want to replace the air), and the result is the total CFM you need for your system.

Do bathroom fans use a lot of electricity?

Finally, the average bathroom fan with a basic light fixture will use 36 watts of energy. Depending on which manufacturer you go with, you could see a watt usage of 10 to 50. The bottom line, the less you use the fan, the less electricity will be consumed.

What happens if CFM is too high?

On the other hand, if your CFM is too high for your room size, it can cause ventilation problems. Too much air results in too little ventilation, which in turn causes high humidity. The excess moisture in the air can then lead to mold and mildew, as well as other problems.

Can two bathroom vents use the same duct?

Well, you can't! You'd often blow air from one bathroom into the other, and local building inspectors wouldn't approve it. But while you can't have two fans with one vent, you can make one fan and one vent serve two bathrooms. This setup requires an in-line exhaust fan.

Will a better bathroom fan prevent mold?

Exhaust ventilation fans play a vital role in preventing mold growth by improving air quality and reducing moisture. These fans work by expelling moist air from inside a building to the outside, thereby reducing the humidity levels that mold spores need to grow.

How many CFM do I need for a 5x7 bathroom?

If your bathroom has an 8' ceiling, the CFM rating for your fan should be as least as high as the number of square feet (5' x 7' = 35 sq. ft.) in the room. So in your case, a 50 CFM fan should work.

How many CFM do I need for an 8x8 room?

To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet. Your extraction fan should be able to adequately exchange the air in an indoor garden once every three minutes. Therefore, 512 cubic feet / 3 minutes = 171 CFM.

Can you have two fans in a bathroom?

Yes, provided both fans are fairly equally powered and will operate at the same time. You obviously don't want one fan significantly more powerful than t'other as it could - theoretically - send its contents out the other fan.

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