Range Hood CFM Calculator – How Many Do You Need?

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The kitchen range hood is one of the most crucial home appliances to have. But what purpose does it serve? It keeps your kitchen free of tiny pollutant particles and most importantly, pushes the toxic cooking smoke and fumes out of the cooking room.

A speedy gust of air released from the kitchen fan does the job and so the amount of the flow of the air is crucial here to push choking smoke and fume out effectively. The airflow weaker than needed will not serve you properly whereas the airflow too mightier than it will be a waste and troublesome.

That is where a kitchen hood CFM calculator becomes so crucial to determine the exact amount of airflow the intended range hood can blow.

But the CFM calculator will fall far short of finding the required amount of airflow to serve your purpose excellently done. To be more specific, there are certain things you have to know rather than determining via a calculator

Say, you can know almost everything that includes the size of the kitchen room, the dimensions of the range hood, BTU and Wattage, and the ducting type, ducting length, number and degree of angle along with the existence of a roof cap.

You can put the said stats in the calculator to have a result but you cannot put the frequency of cooking you may require, the fume-capturing structure of the appliance and the ventilation already the room has.

This is the reason I have planned to write this article to elaborate on how far the CFM calculator can help and inform you of the other factors to make the picture complete. I better make it very clear at the outset that the standards I maintain here are the recommendations from the Home Ventilation Institute – HVI.

A Better Understanding of Range Hood CFM

CFM is the abridged form of Cubic Feet Per Minute by which the airflow blown from the range hood is measured. So this is the rate or measuring standard that expresses the ability of the target appliance how much air it can emit in one minute.

Any modern unit comes with the CFM number stated in the label or on the appliance body. But very often they are found confusing if not wrong.

For a reminder, there is a tendency to provide with a misguided suggestion when it comes to the required and precise range hood CFM calculation.

Suppose a long-established misconception says that the minimum requirement of CFM should be between 600-1200 CFM whereas the ideal fan speed for homeowners is 300 CFM. And the former suggestion is for the commercial set-up.

range hood cfm calculation

Therefore, to save you from being a victim to throw-around wrong number regarding the very crucial range hood CFM; we have attempted to make the process as simple as possible through this calculator.

For your information, whenever you are trying to determine the required number of CFM for your set up, don't forget to include the makeup air – the airflow sucked up by your or for your type of installation or venting or location.

How to Use a Range Hood CFM Calculator?

Before getting on to the section-wise break-down, two things should be pretty clear. And they include putting the number in the calculator without any comma in-between and the decimal points in the right place.

You may not require filling up all the blank spaces but you have to complete any section to get exact output.

That being cleared, the stats you will need to put are:

Location & Range Size

The dimensions and installation type of the kitchen range hood will give the exact answer to how many cfm do I need for my range hood. For the wall mount and under-cabinet type of installation, measure the dimensions of the cooktop from the wall to the front.

And check the dimensions of the cooktop from back to front if it is an island range hood. You should take the measurement in which system the calculator wants (centimeter/inches).

So far the length and location of your cooktop are concerned, HVI has some set suggestions that can give you a near-authentic CFM measurement that will entail nominal modifications.

Counting on Cooking Range Position

Let's see the following table on how to count cooking range position

Cooking Range

Suggested CFM

Minimum CFM

Against a Wall

100 CFM/Foot

40 CFM/Foot

Island

150 CFM/Foot

50 CFM/Foot

Counting on Dimensions of Range Hood

Table 1: For Wall Mount and Under Cabinet Range Hood

HVI Suggest

30”/2.5’

36”/3’

48”/4’

Recommended

250 CFM

300 CFM

400 CFM

Minimum

100 CFM

120 CFM

160 CFM

Table 2: For Island Range Hood

HVI Suggest

30”/2.5’

36”/3’

48”/4’

Recommended

375 CFM

450 CFM

600 CFM

Minimum

125 CFM

150 CFM

200 CFM

BTU or Watts of Your Stove

This is a tricky part. The calculator will have a space bar for both   and Wattage but you better fill either BTU or wattage bar. Filling the both will give you the output counting on the bigger figure.

Another factor you should be careful of is that you need not enter stats of all the burners of your multi-burner cooktop. Put information about the burner you use only. 

Suppose you use only two burners with a heating outage of 1000 BTU each and so you need a range hood matching 2000 BTU only whereas the stove may be of higher heat output. The same rule applies in either type of stoves – Gas or Electric.

The CFM calculator maintains the following recommendations:​​​​​​

  • 100 Watts will require 2.09 CFM
  • 1000 BTU will require 6.1237

The volume of Your Kitchen

The HVI recommendation goes that the range hood should refresh your kitchen ventilating 15 times an hour or once every 4 minutes. To do that, you need a kitchen hood pouring out the exact amount of airflow – at least not lesser if not more. 

You can very conveniently determine the required amount of range hood CFM per square foot using a calculator and in that case, the counting appliance will demand the exact dimensions of your kitchen room – Length, Breadth, and Height.

The simplest way to calculate the required CFM in this regard is to divide the volume of your kitchen with 4. You will find this okay almost always but if you have other means of ventilating your kitchens – such as through window or other- this may vary.

Find the Air-loss Due to Ducting

Until now, we have just learned how to determine the required amount of air to properly ventilate our kitchen using a CFM calculator. But to find the right amount of airflow needed, you have to determine the amount of makeup air. 

To state clearly, if your kitchen needs 400CFM of airflow to well ventilate it; very often you may find that a kitchen hood with the stated amount of CFM is not serving properly. You are at a loss then.

It happens so because if you have a ducted installation and roof cap in the kitchen, a fair amount of your airflow emitted by the kitchen hood will get sucked up for certain reasons. 

Therefore, you need to know how much airflow will get eaten by these factors. To your amazement, you can know this too by using the duct size cfm calculator. You just put the following stats into the space bar of this section to know the amount of makeup air.

Here you go:

  • Ducting Type(Flexible/Non-flex)
  • Ducting Length
  • Number of 90° Turns
  • Presence of Roof cap(1 for Presence & 0 for Absence)

It is recommended that you will lose 7% of total CFM for 25 feet of ducting and for metal/non-flex ducting the loss would be 3%. More to add, 3% Loss of remaining CFM for 90-degree bend and another 3% for your roof cap.

What more you need to consider?

The kitchen hood CFM calculator can give the near accurate CFM number so that you will get rid of cooking moisture, cooking odors, inhouse air pollutants, and choking fumes. But to get the precision output, you must keep some other factors in your consideration.

If your range hood comes adorned with a canopy and sits just over the stove, you will need less CFM compared with the downdraft hood exhaust system.

On the contrary, if you cook in the high-temperature setting, you will need more CFM than the recommended amount.

The duct size cfm calculator will give you the number of CFM sucked up by the existing ducting in your kitchen but if the ducting is bad, your fan can fail to serve the purpose.

Therefore, ducting with the proper dimensions is pretty crucial to come out with the exact CFM amount that will ensure a healthy kitchen.

Having said all that, there is a recurrent question to answer to and that is "Is 400 CFM is enough for a range hood? I will take you to the recommendations made by the HVI and you will find that it is okay for most home set up.

If you want to go upper, many municipalities may not permit you without an additional system for makeup air.

Conclusion

By now, you know all the different ways to determine the airflow speed, dubbed CFM, needed for a healthy kitchen. There is more than one calculating options that let you pick your preferred or convenient one. 

But whatever process you follow as your range hood CFM calculator, the basic recommendations and the crucial factors that you cannot put into a calculator should no way escape your attention. 

However, following the said CFM calculators will make your task way easier.

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