If venting your range hood exhaust through the roof isn’t ideal for you, then venting through the soffit could be more achievable. However, there are some rules you must follow.
Venting through the soffit can be possible when following the rules laid out by the International Residential Code. Below, these rules and their reasoning are explained.
Venting a range hood through the soffit is permitted. It can be the best option if it is the shortest route or if there are already several exhaust vents on the roof already.
Venting Through Soffit Provides Route to Outside
According to Section M1503.3 of the IRC, venting the range hood exhaust through the soffit is a perfectly viable choice, as long as the duct has a smooth inner surface, is airtight, is independent of other exhaust systems, and is equipped with a backdraft damper.
These specifications ensure that there is limited interference from the wind, other exhaust systems, and the quality of the duct.
Although venting through the soffit is allowed, venting into the soffit is expressly prohibited by the IRC.
This is because when you vent into the soffit rather than through it, the majority of the exhaust would likely linger in your attic, leading to possible heat and moisture damage and health concerns.
Why Range Hoods Have to Terminate Outside
Whether your range hood is turned on to reduce heat in the kitchen, get rid of smoke, or another reason, having an exhaust system is important, especially in the kitchen.
Besides heat and smoke, there are a variety of other substances that make cooking without a range hood dangerous.
These harmful substances include carbon dioxide, carbon monoxide, and formaldehyde.
Each of these can cause headaches, nausea, skin irritation, and more when occupants are exposed to them.
If the range hood terminated somewhere in the home, like the attic, these harmful substances could still make their way to the occupied area of the home, where occupants can be exposed to them and begin to feel sick.
Even just the temperature and smell of range hood exhaust is not pleasant to have in the home.
Why the Shortest Ducting Route is Best
Although some duct materials are better than others for a range hood, even for the best of ducts, the fact remains that the longer the exhaust has to travel, the less efficient the process will be.
When exhaust has to travel farther, it begins to lose speed as it travels farther away from the range hood fan. When the exhaust slows down, the process becomes less efficient.
A longer ducting route also means more ducting material. The more ducting material there is, the more likely it is that there will be a leak somewhere in the material.
With all of these factors in consideration, the shorter the ducting route, the better, and sometimes, venting through the soffit is the shortest route.
Other Vent Location Considerations
Distance from Property Lines
As stated in Section M1504.3 of the IRC, to vent your range hood exhaust, the location of the exhaust system opening must be more than 3 feet from property lines.
If your home is close to one or more sides of the property line, under your eaves, where the soffit is located, will be even closer to the property line than the walls of the home are.
In this case, your soffit vents may be closer than 3 feet to the property line, and it would not be permitted.
The reason why soffit vents aren’t allowed to be close to a property line is that your range hood exhaust could enter your neighbor’s property.
If your neighbor has a patio, window, door, or air intake near this property line, those in this space would be subjected to possibly higher temperatures, smoke, and various harmful substances.
Distance from Non-Mechanical Air Intakes
Similar to the property lines rules, range hood exhaust openings must also be at least 3 feet away from non-mechanical air intakes.
These include gravity air intake openings, windows, and doors.
This rule is in place because these openings could allow range hood exhaust back into the home.
If you turn on your range hood to dispel smoke in your kitchen, then a range hood exhaust terminating close to an opening in your home can allow this smoke to come straight back into your home.
Here it is again able to cause respiratory irritation, eye irritation, and can also set off the smoke alarm.
Soffit venting can be less than ideal for meeting this requirement since the soffit often lies just above windows.
Distance from Mechanical Air Intakes
For mechanical air intakes, the IRC dictates that the range hood exhaust termination must be at least 10 feet away if it is not at least 3 feet above the mechanical air intake.
This specification is in place because range hood exhaust exiting at least 3 feet or higher above a mechanical air intake would be unlikely to be drawn back in. This is largely because range hood exhaust is warm and will naturally rise rather than sink towards the mechanical air intake opening.
The 10-feet regulation for is in place because mechanical air intakes actively pull air in. So, there must be a larger space between the intake and the exhaust opening to ensure that the exhaust isn’t pulled back into the home for air quality and comfort reasons.
Benefits of Venting Range Hoods Through Soffits
Can Be the Shortest Route
Despite some challenges with following the IRC, venting your range hood exhaust through the soffit can have the benefit of being the shortest route.
Venting via a route that is as short as possible can be very efficient and lead to energy savings.
No Holes Cut in the Roof
Venting through the roof is an option for range hoods. However, it has the drawback of necessitating cutting a hole into your roof.
Not only is roofing material quite hard to cut through, but cutting through the roofing material can damage its integrity. This could lead to water leaking from your range hood.
The soffit is much easier to cut into and it is sheltered beneath the eaves.
Less Weather Interference
As the soffit is located under the eaves of your roof, it is mostly impervious to weather interference.
The problem with venting through the roof is that rain or snow can get through the backdraft damper since the range hood opening is exposed to the elements.
Rain or snow can also leak into the attic around the vent.
Wind can infiltrate the ducts of your range hood, even with a backdraft damper, creating noise and cold drafts.
This can lower the efficiency of the exhaust system since the flow of the wind inward would counteract the outward flow of the exhaust.
Venting through the soffit will drastically reduce the likelihood of rain and snow getting into the duct and wind infiltrating the duct would also be less likely.
Drawbacks of Venting Range Hoods Through Soffits
Certain Wind Directions Can Cause Issues
Although the soffit is mostly guarded against the elements, from some angles, wind can make its way past and into the vents.
For the most part, the backdraft damper will prevent wind infiltration.
However, the wind can still decrease the efficiency of the exhaust system as it blows against the air trying to escape the vent.
Exhausted Air Can Gather
The wind can also keep exhausted air under the eaves by pushing it towards the roof rather than letting it naturally dissipate into the outside air.
The heat of the exhaust already causes it to naturally rise and gather under the eaves, making it harder to dissipate.
This gathered air can cause damage to your home because of the moisture that it contains.
If your soffit is vented and allows outside air into your attic, the gathered exhaust can enter your attic and possibly the rest of your home, decreasing your home’s air quality (but installing the range hood exhaust near an attic vent is illegal).
Downward Venting is Less Efficient
While venting through the roof can be ideal since heated air naturally rises, when you vent through the soffit, the air is vented downwards.
The exhaust from your kitchen will most likely be warm since the heat from the oven is being captured as well as the heat byproducts of your various kitchen appliances.
That being said, this hot kitchen exhaust will decrease the overall efficiency of the system since flow downwards will be much slower.