One of the most important things to keeping your kitchen clean and safe is choosing a range hood with the right amount of CFMs. CFMs refer to how much air a kitchen range hood can move from one place to another. Having a vent hood that is too small will mean that it’s unable to move enough air to keep your kitchen clean.
Several factors determine the amount of CFMs you need for your range hood. However, as a general rule, you should have 100 CFMs for every 10,000 BTUs your stovetop produces. Another good rule of thumb for electric stoves is to multiply the width of your stovetop by 10 to get the amount of CFMs you need.
While this may sound simple enough, these are only general rules, and much more goes into adequately calculating the amount of CFMs your range hood needs. This article will examine each item and how to ensure your range hood is large enough for your needs. Let’s get cooking!
What does CFM Mean?
You’ve likely heard the term CFM thrown around if you’ve ever owned a fan, furnace, or stove. CFM stands for cubic feet per minute, and the number attached to a CFM hood rating indicates the power of the appliance in question. For example, a range hood with a 200 CFM rating can remove 200 cubic feet of air per minute from your kitchen.
The higher the CFM rating, the more fan power the kitchen hood has. When choosing a range hood, you must select one with a high enough CFM rating but not one that’s too loud or disruptive in your kitchen. Making the right choice is difficult, so we’ve outlined a guide below.
Benefits of Having a Range Hood
Not all kitchens have or are required to have a range hood. Size and space restrictions sometimes prevent houses and apartments from implementing one. However, having a range hood is a lifesaver if you do any cooking and make even a slight mess. This is only true if you have one large enough to meet your needs.
Range hoods, whether recirculating or vented, increase the overall safety of your kitchen. Increased safety is especially true for vented range hoods operating with a gas stove.
Anytime you use a gas stove or oven, carbon dioxide gets created, and the only way to eliminate it from your kitchen is by getting it outside. Local building codes require a gas stove or cooktop with a kitchen exhaust fan vented outside with minimum CFM requirements.
While you can get by opening a window, vented range hoods are much more effective at keeping your kitchen safe.
Range hoods also increase the cleanliness of your kitchen in ways that often go unnoticed until you don’t have one. Running your range hood fan during and after cooking removes fat, grease, smoke, oil, steam, and other airborne particles.
These particles often end up on your countertops, backsplash, or appliances if you don’t have a range hood to remove them.
Range hoods increase safety and cleanliness. While having a range hood doesn’t mean that you never have to clean your kitchen, it does mean that you don’t have to as often or as thoroughly. Range hoods save time during the cleanup process after a meal.
Additionally, range hoods also have great lighting features. Many kitchens, especially older ones, don’t have great lighting, which can be a problem during meal prep and cleanup. The bonus lighting from your range hood can be a lifesaver!
If you ever plan to sell your house, adding a range hood is bound to increase the value of your home. The safety, convenience, and aesthetic it adds to your kitchen are often looked-for commodities with prospective homeowners.
However, each benefit depends on whether your range hood has enough CFMs to do its job. If your hood is too small, it won’t be able to keep your kitchen safe or clean, and it will essentially be a fancy, noisy fan above your stove.
Choosing a Range Hood with Enough CFM Rating
Now that you know how important it is to choose a range hood with the right amount of CFMs, let’s dig into the process. There are four specific things to remember when choosing your range hood, and we’ll go over each in detail.
Type of Range Hood You Have
The type of range hood and how you install it are among the most significant factors determining your range hood size.
An electric range doesn’t need as much CFM rating as gas cooking surfaces. They don’t produce gas or carbon monoxide, and they also don’t have as much heat.
To get you started with your CFM calculation, a rule of thumb is to take the width of your stovetop and multiply it by 10. So, if you have a 48″ stovetop, multiply that number by ten, and you get a CFM count 480. Remember that there are more instructions, but this is an excellent starting point.
Most residential electric ranges will only need a 300 CFM range hood fan.
Gas stoves are slightly more complicated to calculate. The BTU rating of the gas appliance should determine the amount of CFMs on your range hood. BTU stands for British Thermal Units and is the standard measurement for the amount of heat a gas appliance produces.
The BTU rating you need to worry about is the total number of BTUs your stovetop burners produce. Gas burners deliver anywhere from 400 to 18,000 BTUs per burner.
Let’s say you have a range with four burners. It’s common practice to have different-sized burners to accommodate different types and sizes of dishes.
In this example, your stove has two burners of 15,000 BTUs, one that’s 5000 and one that’s 10,000. By adding up all four burners, your total BTU count comes out to 45,000 BTUs.
To calculate the amount of CFMs you need out of your range hood, divide your BTU total by 100. 45,000 divided by 100 comes out to 450, the amount of CFMs your range hood should be. Once again, remember that this is only your starting point and isn’t the only factor to consider.
Most gas appliances will require a minimum of 400 CFM, and the hood must be vented to the outside to comply with local building codes.
Indoor & Outdoor Grills
Grills produce slightly more BTUs than a gas cooktop, outdoor or indoor. However, the formula is the same as with a gas stove. Calculate the total BTUs and divide by 100 for your range hood’s CFM count.
Under Cabinet, Downdraft, and Wall Mounted Hoods
You can install an under-cabinet or a wall-mount range hood, regardless of whether you have a gas or electric stove. This type of range hood installation doesn’t impact the number of CFMs your range hood should have.
Island Range Hoods
If you have an island range hood, choose a more oversized hood with a slightly higher CFM count. A higher CFM count is necessary because your range hood is in the center of your kitchen and pulls more air than a wall-mounted or under-cabinet range hood.
It doesn’t make a huge difference, but adding 50 CFMs to your hood is a good idea to account for the larger kitchen.
A basic rule of thumb for island cooking surfaces is if you have a 30″ range, purchase a hood that is 36″ wide.
The Size of Your Kitchen
The second major factor to consider when choosing your range hood is the overall size of your kitchen. Most kitchens are one big open room, and your range hood will pull air from wherever it’s available. Therefore, the bigger your kitchen is, the larger your range hood should be.
Your kitchen’s total space and volume are calculated using cubic feet rather than square feet. To calculate cubic feet, measure your kitchen’s length, width, and height. Let’s say it’s 20 feet long, 12 feet wide, and 10 feet high. By multiplying 20 x 12 x 10, the total volume of your kitchen is 2,400 cubic feet.
Here’s where things get complicated.
Your range hood should be able to exchange all the air in your kitchen 15 times per hour. This means your kitchen should have utterly new air every four minutes. Now, it’s time to get your calculator out.
Multiply the cubic feet, 2,400, by the number of circulations per minute your hood should have, which is 4. 2,400 x 4 = 36,000 cubic feet per hour.
Next, divide your cubic feet per hour by the number of minutes in an hour, which is 60. 36,000 / 60 = 600. 600 is the minimum amount of CFMs your range hood should be.
If you have calculated CFMs based on your kitchen size and the size of your stove, you should choose the CFM count that’s the highest. So, if your kitchen volume says that your CFM count should be 600, but your stove calculation reached 500, always opt for the higher number.
Your Cooking Habits
Your cooking habits also play a significant role in the CFM count your range hood should be. Here are a few cooking considerations when choosing your next range hood.
Amount of Cooking
Think about how many times you use your stovetop daily and weekly. Next, think about how many burners you have going simultaneously. The more stovetop cooking and grilling you do, the more CFMs you’ll need.
If you do a lot of heavy cooking, you’ll need a better CFM rating with a ducted hood.
Type of Cooking
The type of foods that you cook also make a big difference. Range hoods help remove odors from your kitchen, so you’ll want a larger range hood to eliminate the odor if you cook food with a strong smell.
Style of cooking refers to the types of dishes you cook and how you cook them. Cooking with butter and oil produces lots of smoke, grease, fat, and steam.
Other things such as Asian dishes, bacon, pizza, and fried foods also create unpleasant odors and smoke and grease particles. A powerful range hood can help with creating a more pleasant cooking experience.
What Size Range Hood Duct Do You Need?
If you’re building a new home that doesn’t have existing ducts or vents, then this section doesn’t apply to you. However, if you’re remodeling an old kitchen with existing ductwork that you want to reuse, pay close attention.
Like your HVAC system, your range hood vent can only handle so much air based on size. Most range hoods have round ducts that vent them to the outside. These ducts or pipes range in size from 3″ to 10″. However, most older homes have around 3 and 6-inch vents.
If your new range hood is too large and powerful for your existing ductwork, it will result in too much air resistance and won’t work correctly. If possible, you want the size of the duct to match the size of the range hood. Here’s a short table with the correct dimensions.
- Less than 200 CFM = 3” duct
- 200 to 400 CFM = 4″ to 6″ duct
- 400 to 600 CFM = 6″ to 8″ duct
- 700 to 900 CFM = 7″ to 10″ duct
- 900 to 1200 CFM = 8″ to 12″ duct
- 1200 and higher CFM = 10″ and up duct
The distance and route of your ductwork also affect the amount of CFMs your range hood should be. The farther the distance that air travels and the more twists and turns along the way, the more powerful your range hood has to be.
For every foot of ductwork, you should add one extra CFM. If you’re unsure how long your ductwork is, do your best to make an accurate estimate. You should also add 25 CFMs for every elbow or turn your ductwork has and 40 CFMs if your vent has a roof cap.
If you have a vent that’s 15 feet long and has two turns and exits through the roof, your total CFMs are 105. You should add this total to your current CFM count based on the size of your kitchen and stove.
Calculating the CFM Ratings
By considering each of these things, you’re now ready to calculate the amount of CFMs your range hood has to be. Here’s what the step-by-step process looks like.
- For an electric stove, measure the width of the top and multiply that number by 10.
- For a gas stove, add up the total BTUs of the burners and divide that number by 100.
- Measure the volume of your kitchen, which is length x width x height.
- Multiply your kitchen’s cubic feet by 15 since that’s the number of times your range hood should recirculate the air per hour.
- Divide that number by 60 to get the cubic feet per minute of air your range hood should circulate.
- Compare this with the CFM total that your electric or gas stove equals.
- Choose the higher of the two numbers as your base CFM number.
- For each foot of existing or to-be-installed ductwork, add 1 CFM.
- Add 25 CFMs for every turn in your ductwork.
- Add 40 CFMs if your vent goes through the roof and has a roof cap.
- Take this total CFM count and choose a range hood to match.
Let’s use the example above: your kitchen was 2,400 cubic feet, and your stove totaled 45,000 BTUs. Your kitchen indicated a minimum of 600 CFMs, while your stove stated a minimum of 450 CFMs. By choosing the higher of the two amounts, your base number of CFMs is 600.
Next, the length of your ductwork, the turns, and the roof cap added 102 CFMs. This comes out to a total of 702 CFMs. Finding a range hood with a minimum of 700 CFMs would be best. Choosing one that’s 50 to 100 CFMs higher than the minimum requirement is a good idea to be safe.
However, if you have preexisting ductwork to vent your range hood, ensure it’s compatible with your CFM count. If the ductwork is too small, you may have to replace it with new ductwork that’s the right size.
Other Tips and Tricks
Another thing to consider when sizing your range hood is whether or not it’s vented or recirculated. Vented range hoods take air from inside your kitchen and carry it out of your home via the ductwork discussed above. However, a recirculating range hood has internal filters and fans that suck the air into itself, clean it, and send it back into your kitchen.
While studies have shown that recirculating fans are highly effective, they also have specific stipulations if they hope to be successful. Replace the carbon-charcoal filter inside the hood every three or four months to boost effectiveness. You may also have to clean your kitchen more often since a ductless range hood doesn’t get all the steam and smoke out.
Cleaning your kitchen is extremely important whether you have a vented or recirculating range hood. Hoods go a long way in helping with the process, but there will always be trace amounts of grease, fat, and debris that your hood cannot eliminate.
Is It Better to Have Too Many CFMs or Not Enough?
As long as your ductwork isn’t too small to handle a larger range hood, bigger is always better. Bigger range hoods with a higher CFM count are more effective at pulling air out of your kitchen and keeping it clean.
However, having a range hood with a high CFM count must be within reason. It would be best to never pull more air out of your kitchen than what is already inside it. Remember that you’re pulling conditioned air out of your kitchen with a vented range hood and sending it outside. This could result in higher heating and cooling bills if your CFM count is substantially higher than it has to be.
Do I Need Makeup Air?
Makeup air is one of the most common myths with range hoods. Makeup air is the air that’s brought in from outside your kitchen to supplement the air that your range hood is removing. However, this is only necessary when your range hood CFM exceeds 1200, and you have a small kitchen. You rarely need to install a makeup air system to supplement your range hood unless your local building code requires it.
Is 300 CFM enough for a gas range?
300 CFM is enough for a gas range if it only produces 30,000 BTUs or less. Remember, take the number of BTUs and divide by 100 to get the minimum CFM count of your range hood. However, most gas appliances will need at least a 400 CFM rating.
What is the minimum vent duct size for a range hood?
In modern range hoods, the minimum vent size is 6″ for a 400 CFM-rated hood and can range up to 12″ for a 1200 CFM-rated hood. Most residential four-burner gas cooktops will need a vent of 6″ to 8″ in size. Most six-burner professional-grade gas cooktops need an 8″ to 10″ in diameter vent.
What does the Sones rating for a range hood mean?
Sones are loudness units and refer to how loud or quiet your range hood fan is during operation. The lower the sone rating on your range hood is, the quieter it will be during operation. If noise in the kitchen is a big deal for you, you should look for a range hood with a Sone rating of 2 to 4.
What is a good CFM for a range hood?
A good CFM rating would be around 100 CFM above the minimum ventilation level. For example, if you need 200 CFM, then 300 CFM would be good.