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a range hood

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During this step of the range hood buying guide, we will be checking one last important aspect of choosing your future range hood's power: kitchen size. Afterwards you'll find a very important notice on meeting the range hood code requirements and it's connection to poisoning.

Step 3.3 How to choose the amount of power - Kitchen Size

We're going to take a look at how big your kitchen is, because its important that the power of your future range hood matches the size of your kitchen. Remember how CFM stands for Cubic Feet Per Minute? Well, it’s recommend (by the Home Ventilating Institute) that your range hood should be able to cycle all the air in your kitchen 15 times per hour. That means that we will need to size up your kitchen. For the people with a phobia for numbers, there’s going to be some math involved. But, don’t worry, it’s 2nd grade math. We promise it’ll be the last time you will have to do math in this guide. For the PDF people: smooth sailing for you!

In this step of this range hood buying good, we're going to take a look at how big your kitchen is, because its important that the power of your future range hood matches the size of your kitchen. Remember how CFM stands for Cubic Feet Per Minute? Well, it’s recommend (by the Home Ventilating Institute) that your range hood should be able to cycle all the air in your kitchen 15 times per hour. That means that we will need to size up your kitchen. For the people with a phobia for numbers, there’s going to be some math involved. But, don’t worry, it’s 2nd grade math. We promise it’ll be the last time you will have to do math in this guide.

Bust out your tape measure and do the following

If you're using our PDF, you won't have to calculate a thing. All the math will be done for you. Just fill in your measurements and voilà.

  • Measure the floor of your kitchen (in feet).
    Measure both the length and width of your kitchen in feet and write them down.
  • Multiply them.
    For example, if the length of your kitchen is 15 feet, and the width of your kitchen is 12 feet. If we multiply them, we will get (15*12=) 180 square feet
  • Measure the height of the ceiling to the floor
    (in feet).
    Write down it down (you’ll need it later). For example, let’s say the height from the ceiling to the floor of your kitchen is 8 feet. Multiply this 8 feet with the amount of square feet of your kitchen floor you just calculated, which was 180 in our example. We will get 8*180= 1440 Cubic Feet.
  • Calculate the CFM
    Remember how CFM stands for Cubic Feet per Minute? Well, we just found out the kitchen in our example is 1440 Cubic Feet. You’ve read in the intro of this part that it’s recommended to get a range hood which is able to cycle all the air in the kitchen 15 times per hour, which comes down to once every 4 minutes What we need to do is take the amount of Cubic Feet we’ve just calculated and divide it by 4. This gets us 1440 / 4 = 360 CFM.
    A range hood of this much power will be able to cycle the air in your kitchen every 4 minutes. Write this number down.

PDF

Question 7: Write down the length and width of your kitchen floor, as well as the height of your ceiling.

Step 3.4 Pick your CFM

The moment has arrived: we're finally going to pick our range hood power! If all went well, you will now have four different CFM numbers, based on the following:

  • Duct size (two different CFM ranges, e.g. 0-400 and 400-600)
  • Stove power (BTU)
  • Kitchen size (Cubic Feet)

Which one do we choose? What you will need to do is compare the CFM you got from both your stove and your kitchen size, and simply pick the highest number.

Remember how your duct size gave you two different CFM ranges? One which fit the recommended duct size and one which fit the minimum duct size? Take the highest CFM number from either your stove or kitchen size and compare it to both the CFM ranges you've gotten from your duct size. This highest number will need to fit into either the recommended CFM range or the maximum CFM range.

For example, let's say your house has a 6 inch duct. According to the table below, you could technically go either for a 0-400 CFM range or a 400-600 CFM range. The 0-400 is the recommended range, and the 400-600 CFM is the maximum CFM range your duct will allow.

In our previous examples, our gas cooking stove gave us 320 CFM, our electric cooktop gave us 232.50 CFM, and our kitchen gave us 360 CFM. We will pick the highest number out of those, which is 360 CFM. When we look at the duct size table from step 3.1 (see below), it fits neatly in the 0-400 CFM range for our 6 inch duct.

PDF

Question 8: You don't really have to do anything. The PDF has picked out the highest CFM (+ range) for you.

Power (CFM)

Minimum
diameter duct
(inches)

Recommended
diameter duct
(inches)

0-400

4

6

400-600

6

8

600-900

8

10

900-1200

10

12

1200+

12 *

12+ *

* Depends on the length of the duct, the amount of bends, the static pressure and the type of range hood motor (axial fan vs centrifugal fan).

Congratulations, you've chosen the power of your future range hood. Great job! Give yourself a high five. Next, we're going to shortly highlight some other important range hood features. What? More things? Don't worry, it's just one page of features you will have to pay attention to when buying a range hood. There's no math involved whatsoever. But, before we get to it, please read the following notice on high CFM range hoods.

Range hood code
requirements & poisoning

Poison

We know that range hood code requirements isn't the most interesting topic, but for your own safety please read on. The following information is what range hood manufacturers usually won’t tell you, even though it’s very important. It’s actually so important, the law demands it. However, since the range hood manufacturers want and need to sell as many of their range hoods as possible, some have  

chosen to withhold  this information, as could mean the difference between buying an expensive model and a cheap(er) one. Since we don't play that game here at Rangehoodguide.com, please read on.

Like we've shortly mentioned before, some people immediately want to buy the biggest, baddest commercial grade range hood they can get their hands on and install it in their home kitchen. You might have a big family and therefore need to prepare a lot of big dinners. Others just want to impress their friends. A nice big and shiny range hood in the kitchen can be a great eye catcher, right? 1200 CFM? Make it 1600 CFM! Better to be safe than sorry, right? No. Not only would that be overkill for the average household and would consume large amounts of energy, it would actually be very dangerous to put it in your residential home without the proper precautions, as it will likely create a backdrafting problem. A what problem? Let us explain.

As you know, range hoods suck up air from the kitchen and export it out of the building. As you know, the higher the CFM of the range hood, the faster the air is transported out- side. Obviously, the longer a range hood is turned on, the more air it will transport outside. When that happens, it will create a shortage of air within the kitchen (a negative in-house air pressure), because a large amount of air is transported out of the kitchen, but nothing is coming in. To balance out the air pressure, new air (called makeup airwill usually come in through random air leaks 

throughout  the house (called backdrafting). However, due to houses becoming more and more air-tight and well-isolated, the makeup air has to come from other places. In practice, this usually means it comes in through undesirable exhaust routes (e.g. fireplace, furnace, dryer vent, hot water heater), which might cause carbon monoxide and other harmful pollutants to be sucked into the house and cause (carbon monoxide) poisoning.

This guy gets it. And he's wearing a hard hat, which means he knows a lot about building stuff.

According to the International Residential Code (IRC) 2015 (M1503.4), if you want to install a range hood with more than 400 CFM, it’s required to install a makeup air system which can move fresh air back into the kitchen at the same rate as the range hood can transport air out of the kitchen. This air intake system needs to have at least one damper, either a gravity damper or a damper which opens automatically once you turn on your range hood. Not having such a makeup air system means that you’re in violation of your city's 

or state’s building code. However, check your own state’s building code, because the CFM threshold to supply makeup air may vary from state to state. (E.g. in the state of Minnesota the threshold is 300 CFM.)

Luckily, some manufacturers have started to design such makeup air systems, so that people will be safe from harm by meeting the range hood code requirements. They usually include a sensor of some type which senses when to open up the damper and let the fresh air in. Example:

Broan Makeup Air System 6 inch

(This guide will be continued on the next page.)

Next page: almost done!

Glad you've made it this far. The next page will be the last of this guide to buying a range hood. Read on!

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