When you install a range hood in your kitchen, you’re investing in the health of both your home and your loved ones. One of the core aspects of finalizing range hoods is choosing which type of duct to go for. The duct will act as a pathway that leads polluted air outside of the house. Selecting the right material for this pathway is essential. That is why in this read, you’ll be learning about the several options you have for ductwork and which material is best for the job.
Rigid duct is the best type of duct for venting a range hood. Some of the other options that you have are flexible duct, rectangular duct, semi-rigid duct, and PVC duct.
Table of Contents
Can I use flexible duct for range hood?
Flexible duct for range hood is not allowed by the IRC (International Resident Code) for good reasons. According to the code, ductwork must have a rigid inner build. This restriction is mainly because of safety reasons. A flexible duct is not suitable because grease and dirt can build up with time and may potentially lead to a house fire. Other than the basic safety reasons, a flexible duct is extremely difficult to maintain and clean. Due to most of the material being made from either aluminum or plastic, the durability of this duct is relatively low as well.
The ductwork is not immune to debris and dust from the outdoors. Combine that with the toxic airborne waste that is disposed of from the kitchen, the flexible duct will not be able to withstand this much dirtiness in the long term. It would become a hassle to fully clean it. Simply put, it does not comply with the required ductwork standard imposed by residential codes. You don’t want to take the risk either because if things go south, there’s a high probability that your insurance won’t cover the loss either since you violated the residential code. Unfortunately, flexible duct does not come anywhere close to rigid duct in terms of performance and it’s a risky pick.
Can I use rectangular duct for range hood?
Rectangular duct is fine for range hoods but not the best option because of its proneness to grease buildup. As we mentioned previously that grease piling up in the ductwork is common for even kitchens that have minor cooking sessions here and there. At the end of the day, you have to maintain your duct, and maintaining round ducts is easier. This is because rectangular ducts have corners and edges where dust and grease are set up easily. On the contrary, round ducts have no corners so dirt settles at the lowest point in a straight line making it easier to clean.
Furthermore, rectangular ducts are less effective in directing airflow as compared to round ducts. The latter provides better angles of airflow and also has decreased chances of air colliding with the duct. To sum it up, rectangular ducts are fine to use but if you’re looking for maximum efficiency, circular ducts are the way to go.
Can I use semi-rigid aluminum duct?
Semi-rigid duct is a better version of flexible duct and offers more stiffness and stability in the duct. However, semi-rigid aluminum ducts are not recommended because of their low-quality material. Aluminum in general is not the best material for ductwork because the material is not as strong as it needs to be. Although it does a relatively better job at directing airflow than flexible duct, it still doesn’t fully give you the durability you’re looking for. Semi-rigid duct will barely last a couple of months before it would need costly repairs. So, the bottom line is that this isn’t the best option in the market either.
Can I use PVC duct?
PVC duct is not the ideal duct for range hoods because it does not have a steel composition. Much like the reason for the prohibition of flexible duct, plastic PVC duct is not allowed to be used under most local codes. Though certain areas might allow it under very strict conditions that are rarely met, the verdict remains the same. Some of these conditions include the PVC duct being solvent cemented and installed under a concrete slab. Typically, PVC ducts are flexible and made from a material that is vulnerable to the wear and tear that ductwork normally goes through. It would also be quite difficult to clean the PVC duct since it does not have a smooth internal surface.
Rigid duct for range hood
Now that we’ve addressed the options you shouldn’t go for when choosing ductwork, it’s time to discuss rigid duct. Rigid duct is the ideal duct for range hoods. It is the most durable and efficient option you have because of its toughness. Rigid duct fulfills every requirement proposed by the IRC for range hood ductwork. It has a smooth surface and comes in either stainless or galvanized steel, which are the best materials for this job. Unlike plastic and aluminum, steel ductwork is far easier to maintain. Cleaning is occasionally needed and doesn’t require extra effort in getting rid of the grease and debris.
Durability is the last thing you need to worry about with rigid ducts. The material is strong enough to withstand the harshness of different weather conditions without needing repairs every once in a while. Although rigid ductwork might cost more than flexible and semi-rigid ducts, it’s an investment that will serve you for at least a decade or two under timely maintenance. Whether you need it in a rectangular or cylindrical shape, rigid ductwork comes in both shapes to complement your range hood.
Where should I vent the range hood?
A frequently asked question regarding range hoods is where the ductwork should lead to. Your range hood should always be vented outside with no exceptions. Vents have the purpose of directing polluted air from the kitchen to the outdoors. Under no circumstances should you vent into the attic or a wall. Toxic air that is released from your kitchen must be led outside through the vented duct. Range hoods play a major role in maintaining the air quality of not just your kitchen, but of the overall house. If you vent indoors, you’re just temporarily getting rid of the polluted air and compromising the health of your loved ones.
Therefore, try venting outside and as closely to the kitchen as possible. The range hood’s duct must not be extended unnecessarily as it can impact the airflow. A short pathway that has no obstacles and leads outside is the most preferred. If making way for the duct seems to be a problem for your kitchen layout, consider opting for alternatives, such as ductless range hoods. These hoods do not require ductwork but are not as efficient as ducted ones. However, you can opt for them if you have a small kitchen with space issues.
How big should the duct be for range hood?
The size of the duct is dependent upon the range hood’s working. The more powerful the range hood, the bigger ductwork would be needed. For instance, range hoods with a CFM of 400 need around 4 inches of duct for air to pass through freely. CFM is a measurement used to denote the competency of range hoods. This recommended duct size will continue to increase as the CFM increases. Furthermore, the width of the duct should not be too less as it can cause the air to make unnecessary noise during operation. Smaller ducts are less efficient in air disposal as overflow leads to more resistance in the pathway. Here is a table to give you an idea of the ideal duct size in relation to CFM:
| Range Hood CFM | Recommended Duct Size |
| 400 | 4 inches |
| 600 | 6 inches |
| 900 | 8 inches |
| 1200 | 10 inches |
Once you have the size figured out, the next measurement is the length of the duct. Remember, the shorter the duct, the better the airflow. The same goes for elbows used in the duct. Your ductwork should not have more than three elbows. Otherwise, the chances of air being directed back to the kitchen go high due to more resistance being present in the way. Lastly, the duct should be facing upwards at the start of the hood. This helps polluted warm air rise from the base and get shifted outdoors through the vent.
Here is a detailed article on selecting the right range hood duct size: Range hood duct size guide
Should I make my range hood’s duct smaller?
Ducts are not supposed to become smaller. Bigger ducts help in the circulation of air. You should not cut down the size of the duct unless there’s an absolute necessity. Such cases are rare and homeowners generally prefer expanding the size of their ducts instead of trimming them. Expansion of duct improves airflow and reduces noise whereas reduction does the opposite. If you’re worried about pests and debris making their way into the duct, consider opting for dampers instead.
Conclusion
Duct work is costly, but it can cost you more if it’s done improperly. Ensure you’re going for the right material, size, and design before you finalize the investment.
