What Range Hood Duct Size Do You Need? A Detailed Guide

Installing range hoods in your home have many benefits, from removing smoke and steam to better-looking kitchens. The primary problem homeowners face when choosing range hoods is getting the right size ductwork to go with them. 

Duct size depends upon the range hood’s cubic feet per minute (CFM). A small duct size is needed for a hood with lower CFM, while a range hood with higher CFM will require a large size duct. The standard sizes available for round ducts are 4″, 6″, 8″, 10″, and 12″. A suitable duct size enhances the efficiency of the range hood.

In this article, I will discuss choosing a suitable duct size and other related information so you can pick the perfect duct for your range hood.

Why is choosing the right range hood duct size important?

As you might have guessed, size does matter when it comes to your range hood ductwork and the vent or range hood itself. If you choose an undersized duct system, air won’t flow freely through your range hood. It could lead to poor airflow and less than-optimal extraction performance. 

On the other hand, if you go with a system that’s too large, it will pull in more air than necessary, making your unit work harder and use more energy than necessary.

In short, an improperly-sized duct won’t be able to exhaust the cooking air efficiently, meaning you’ll be wasting energy and money unnecessarily trying to keep your kitchen clean and smelling good. To run a range hood at maximum productivity, install a suitable duct according to your hood fan’s CFM rating.

What is the minimum size for a range hood duct?

The minimum allowed duct size for a range hood duct is 4″, which is suitable to use with range hoods with a 400 or less CFM fan. Range hoods with a higher CFM will require wider ducts accordingly. Remember that a small duct will not let the hood perform to its optimum capacity, so the recommended sizes for each CFM are more than the allowed size.

How to measure a range hood duct size?

You don’t have to go and measure anything physically. Read the manufacturer’s manual and check the CFM of the range hood and the recommended duct size. Following are the allowed and recommended duct sizes according to the range hood’s CFM rating:

CFM Rating Allowed Duct Size Recommended Duct Size
0 – 400 CFM 4” 6”
401 – 600 CFM 6” 8”
601 – 900 CFM 7” 8” – 10”
901 – 1200 CFM 8” 10” – 12”
1200 CFM and above 10” 12”
Range hood duct sizes vs CFM

Range hood duct length considerations

Along with the diameter, range hood duct length should also be considered when installing a hood. According to experts, the range hood ductwork shouldn’t run longer than 30 feet. Consider the following suggestions when running the ductwork:

Short length

The length of the duct directly affects the efficiency of the range hood. A shorter duct run is better than a longer duct run as the cooking air will have to travel only a small distance to reach outside. Also, a shorter duct run helps get the exhaust air out efficiently when your duct diameter is slightly undersized.

Fewer elbows

A range hood duct running smooth and straight can help exhaust cooking air more effectively than a duct with bends, as changing the direction of the duct adds resistance and unnecessary pressure to the air passing through it. So adding few or no elbows is a better choice. If adding an elbow is inevitable, try to shorten the duct length. Reduce the ductwork length by 10″ for each elbow or a 90 degrees turn. It means that if your ductwork has one elbow, the ductwork length should be a maximum of 20 feet.

Upward ducting

Hot air always moves upwards, so an upward duct is the most logical consideration to throw the cooking air out of your kitchen faster. It will ensure that the hood will operate in the best possible way. 

Frequently Asked Questions

Do range hoods need to be vented?

Venting the cooker hood outside depends on the range hood you are installing. A ductless hood does not need to be vented outside, and it will recirculate the air into your kitchen. In contrast, a ducted range hood will exhaust the cooking air outside the house. It works by pulling grease and fumes away from your stove’s burners before entering your home’s air supply, so ducted range hoods are a better choice than ductless hoods for clean air.

Which is a better range hood duct shape: round or square?

Round ducts for range hoods are better than square-shaped ones because round ducts offer less resistance to the passing air, and they use way less metal than square ducts. These qualities of round ducts make them better than square ducts in terms of cost and efficiency.

Can I use flexible ducting for a range hood?

Experts don’t recommend the use of flexible ducting for range hood ductwork. A flexible duct is a waste of money as it isn’t sturdy, is made of cheap materials, and is difficult to maintain. 

On the other hand, a semi-rigid or rigid duct is better than a flexible one, with a rigid one being the best of them all. A rigid duct is durable and long-lasting as it’s made with higher-quality materials and offers better airflow than a flexible duct.

You can read more about this here: What duct is best for a range hood?

What is an ideal duct material for a range hood duct?

Stainless steel is ideal for a cooker hood duct as it is durable and facilitates airflow through it to the max. Using PVC or aluminum ducts is not recommended as they don’t last very long, making them a bad investment. 

Does a range hood duct need to be insulated?

You can insulate the hood duct, but it is unnecessary. However, insulating the duct can reduce the blower noise significantly if it is in line with the ductwork. Also, it will prevent the smoke from leaking through the joints into the attic.

Conclusion

Buying a range hood is easier than you might think. The most important thing to remember is duct size, as each range hood will have very different ventilation requirements according to the hood fan’s CFM. No matter what size range hood you choose, ensuring that your ductwork is up to snuff is essential. I hope this article has answered your concerns regarding range hood duct sizes for better-performing hoods.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

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