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Range Hood CFM Calculator

By Annie & Oak Farmhouse Sinks September 28, 2021 0 comments

Search no further and be a range hood CFM calculator yourself! 

In this article, we'll provide you all the formulas you need to calculate the CFM for range hoods. We'll even show you how to apply them with the right steps all laid down for you below.

Important Factors to Know for Calculating CFM for Kitchen Range Hoods

Let's get to know some important things first before we dive right into calculating the total cubic feet per minute (CFM) for your kitchen range hood.

Size of Your Kitchen

First of all, measuring the ceiling height to each and every corner of your kitchen is necessary. You should be familiar with the total volume of your kitchen.

You will know its overall size by applying the formula of length x width x height.

According to the National Kitchen and Bathroom Association (NKBA), a small kitchen is only sized 70 square feet or less. And the larger room size is over 200 square feet.

These sizes matter a lot since they inform you of the overall CFM you need for your kitchen range hood.

white kitchen interior

For example, you need a larger CFM hood if your room size is larger than 2000 cubic feet.

But before we teach you how to calculate the CFM you need for your range hood, you should know first that kitchen hoods should be capable of ventilating air 15 times per hour. This means it finishes circulating air flow every 4 minutes for effective removal of cooking odors.

By knowing this, you will be able to calculate the minimum CFM you need for your range hood in 3 simple steps:

 

  • Measure your kitchen's total cubic feet and multiply it by 15
  • Divide the answer from Step 1 by 60 minutes
  • The answer you get from Step 2 is the minimum CFM for your range hood.

Position and Size of Your Kitchen Range

Expect an increase in cubic-feet-per-minute (CFM) requirement depending on the position and size of your range:

white kitchen with range hood

  • Add 100 CFM of air flow per linear foot of the range (while considering the stove width) IF your electric or gas stove is against a wall.
  • Add 150 CFM of ventilation per foot of your stove's length IF you are planning to get ISLAND range hoods.

Type of Kitchen Range

Aside from what's mentioned above, there's one more thing you need to be familiar with.

The type of range (gas or electric stoves) is an essential factor for calculating the required cubic feet per minute (CFM) range hood vent.

Electric Stove

For an electric range, there's no need to go over complex math. You only have to find the stove width and multiply it by 10. And that will be enough for getting the minimum CFM range hood.

black kitchen range and range hood

Gas Stove

But gas stoves are a bit different compared to the electric cooking surface. Aside from producing more hot air, a gas stove is also measured in British Thermal Units (BTU output) [1].

For those who don't know, BTUs are the measure of energy that's necessary to raise or cool one pound of water by one degree Fahrenheit at sea level.

It is possible to have different BTU ratings in gas burners. One burner could have 10,000 BTUs and the other could have 15,000 BTUs.

You can usually find the BTU rating of your gas stove in the manual which comes when you purchase your range hood.

wooden kitchen

If you did, try typing the brand and model of your hood on Google to see if you can source any details or specs.

Once you have all the specs, you can now find the CFM of your vent hood:

  1. First, add the total BTU ratings of all the burners.
  2. And then divide the answer by 100.

Grills

You should be familiar with range hood CFM calculation for grills too. Just in case you are planning to get a range hood outside.

But don't worry. You don't have to memorize another set of formulas. A grill also requires the same minimum CFM requirements as a gas stove so you're safe.

Although be aware that grills typically produce warmer air so you will get more CFM from this. 

Also, take note that the CFM value you get for the hood here will only be the minimum — regardless of whether you're using a grill, electric, or gas stove.

To get the overall CFM for your range hood fan, there are only a few more steps left.

Size of Your Ductwork

Calculating the duct length or total duct diameter will be the last step to figure out the required CFM for your range hood.

 

Ductwork is measured by:

 

  • Adding 1 CFM for each foot of the metal pipe.
  • Adding 25 CFM for each turn in the duct.
  • Adding 40 CFM for a roof cap (only if you have one).

 

How Often You Cook

Before we end, there's one optional factor that affects the necessary CFM for a range hood as well — how often you use the kitchen.

lady cooking

You should add another 200 CFM if you often cook regardless of the type of stove you are using.

Now, Let’s Calculate CFM for Your Range Hood!

You can get the total CFM rating for your new range hood fan now — but in two ways:

 

  1. Just add 200 CFM to the minimum CFM you calculated for the kitchen range earlier in the first section of this article ("Size of Your Kitchen"). You will only use the CFM you got based on the type of range you have.
  2. Or, you can do a more complicated process that involves ductwork and more.

 

This is how the second option goes in case you want to explore a more complex method:

 

  1. Add all the CFM you got earlier from measuring your ductwork — CFM for each foot, each turn, and additional CFM for the roof cap.
  2. Compare the minimum CFM you previously got between the kitchen size, range size and its position, and the type of range you own.
  3. Choose the higher CFM among the three.
  4. Add the said CFM to the overall CFM you got for your duct work.
  5. You can also add 200 CFM at the end if you frequently cook.

 

FAQs

Do I Need Makeup Air?

You do not need makeup air for your range hood unless it is required:

 

  • You should only get one if your building code says so.
  • Or if your kitchen exhaust fan often sucks all fresh air out of your house. So, it's either you cook 24/7 or you have a surprisingly high CFM range hood fan in a very small room.

 

When Do I Need to Turn On and off the Range Hoods?

The recommended practice is to turn on the exhaust fans 10-15 minutes before you start cooking. And you should leave them running for a while even after you've finished cooking.

This is so your range hood can effectively filtrate all the dirty air and throw it out all the way to the roof cap.

Is Higher CFM Great for Range Hoods?

Generally, it is better for range hoods to have higher air flow — most importantly if you have a large kitchen room because:

 

  • This keeps the air in the room cleaner and safer.
  • It makes it possible for you to cook a variety of foods. This includes steamed foods you can serve from early morning to late night.

 

But we do not recommend you to get a high CFM range hood if you have a small kitchen.

As mentioned earlier, you'll run out of clean air when this happens. The air that lingers in your kitchen will feel dry and uncomfortable in this situation.

Conclusion

See how simple it is to figure out the right CFM you need for your kitchen range hood? You can become a range hood CFM calculator in just 5 minutes without any complex math formulas.

Just add, multiply, and divide — and you have your CFM right away.

Hopefully, you were able to understand everything our team shared with you. You can always go back to this article if you ever forget some steps in between.


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