soffit vent – HVAC-BUZZ

Dryer ventilation is a building code requirement. When it comes to venting appliances like dryers and bathroom fans, the most commonly used exit point is the house roof. However, there are a number of reasons why this might not be the best choice—or even possible—and you have to start considering other options, such as a wall or soffit (the underside of the roof overhang, or eaves). The International Residential Code (IRC) does not state that dryers can be vented through soffits. However, it does provide enough information for us to come to this conclusion based on the general dryer ventilation installation requirements set out in the code. We look at this information, reasons why you should and should not vent through the soffit, how to vent through the soffit, and more! The IRC Does Not Prohibit Venting Through Soffits Whenever I am making an alteration to my house, whether it's something simple, like installing a new bathroom door, or something more complex, like venting an appliance, I always start by checking the building codes. Sometimes the code will explicitly say you can or cannot do something. However, if the codes were to plainly say everything that you can and cannot do, they would be ridiculously long and extremely difficult to navigate. As such, some rules are implied through a collection of adjacent regulations. In the case of venting a dryer through a soffit, there is no explicit statement of yes or no. However, we can suppose it to be acceptable with regards to the IRC as long as venting through the soffit does not contravene any of the venting rules found in Section M1502 of the IRC, which governs Clothes Dryer Exhaust. Soffit Dryer Vent Positioning According to IRC M1502.3: “Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions. If the manufacturer’s instructions do not specify a termination location, the exhaust duct shall terminate not less than 3 feet in any direction from openings into buildings, including openings in ventilated soffits.” This means all exhausted dryer air must be released outside, which makes sense when you think about all the damage moisture-laden air can do inside a house! (You can get an idea of just how bad it is by reading my article on Reasons Why Having No Ventilation in a Bathroom is Terrible). Venting through the soffit would meet this requirement of exhausting outside. The IRC often gives final installation authority to manufacturers, such as is the case here. The reason for this is that all dryers are different and to govern their installation in the same way could end up creating problems. If your dryer manual says "do not vent through a soffit", then to do so would be contravening building codes. However, the IRC does make provisions if the manufacturers do not specify installation instructions. In this case, if the manufacturer has not stated where the vent can be located, it must be more than 3 ft (914 mm) from openings in the building. This makes universal sense because it prevents exhausted air from flowing out of the duct and straight back into the house. Printable Dryer Venting Checklist The IRC specifically mentions openings in ventilated soffits, because passive soffit vents are frequently used to ventilate attics and other upper-story rooms. If you can't vent the dryer through the soffit so that the exit is more than 3 ft away from all of the ventilated panels, then venting through your soffit would contravene the code. Benefits of Venting a Dryer Through a Soffit Although less common than roof venting, there are several benefits of venting a dryer through a soffit. These advantages include: Building Heat Conservation The dryer ducting channels warm air. As the soffit ducts are usually horizontal (although there is a slight slope down as per the building regulations), gravity does not play a large role in moving this warm air outdoors. Instead, the warm air remains in the ventilation duct which can create a warm front of air, which remains in the house. Outside air is prevented from flowing into the background due to this warm air "barrier", which can keep your house warm during winter. Minimized Effects of Wind and Weather Installing the dryer exhaust termination in the soffit means that the vent has a unique angle on the underside of the rooftop. Wind does not often flow strongly at this angle and thus very little back-draft is possible. The vent will also be less likely to cause leaks in your house because of its sheltered position in the eaves (when was the last time you saw rain being directed upwards!). No Need for Hole Through Your Roof By installing a dryer vent through a soffit, you do not need to create a new hole through your roof. If your roof is already housing your attic vents, bathroom exhaust vents, etc., then the dryer vent may overcrowd your rooftop. Furthermore, using a soffit vent helps to keeps your house leak-free because every time you make a new hole in your roof, there is a certain degree of compromise to the weatherproofing and you naturally increase the risk of leaks. Drawbacks of Venting a Dryer Through a Soffit There are also several drawbacks of venting a dryer through a soffit. These disadvantages are: Short and Straight Requirements To operate efficiently, dryer ventilation systems should be as short and as straight as possible. This will, unfortunately, dictate where the ventilation exit can be located. For dryers in basements or other below-ground locations, the best location for the vent would be at or near ground level, which is not near the soffit, so it is not a viable option. If the dryer is located in a central room, you will have to assess the route to the soffit; if it involves too many turns, then it might exceed the allowable ducting length for dryers, which we discuss later on in this article. Backdraft Damper Requirements Another drawback of venting a dryer through a soffit is that the exhausted air is warm and naturally wants to rise. So, when it is released from the termination vent, there is a high chance of backdraft with the exhausted air. To minimize the risks thereof, dryer vents are required by code to be fitted with backdraft dampers. Soffits on Upper Stories Lack Accessibility Another drawback of venting a dryer through a soffit is that the soffit dryer exit is more difficult to clean regularly if they are on the soffits of upper stories as the vent will only be accessible with a ladder. However, it is vital that the vent be cleaned regularly in order to prevent lint build-up and outside debris (including animals and nests) from collecting onto the exit. Such a build-up creates a significant fire risk. Furthermore, the debris build-up can cause decreased efficiency and reduced speed of airflow. Since these soffit vents are out of sight, they are more likely to be forgotten by the homeowner and not maintained. It is important to note that soffit vents are considered to be more accessible than roof vents as long as they are not on the soffits of upper stories. Never Vent Into a Soffit While the IRC does not prevent you from venting your dryer through the soffit, it does state clearly that a dryer may not be vented into a soffit. This can be found in IRC section M1501.1 (outdoor discharge): “The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section 1504.3. Air shall not be exhausted into an attic, soffit, ridge vent, or crawl space.” There are two main reasons for this prohibition: The first reason is that it would cause a build-up of moisture in the soffit, walls, and attic, which can lead to structural damage, electrical damage, rust, and mold. Furthermore, it can attract rodents and insects into your attic and lead to animal-related damage and bacterial growth. The second reason is that lint will build up in the soffit, walls, or attic, which poses a severe fire hazard for the home. All Normal Installation Regulations Still Apply Manufacturer Instructions Take Precedence As I mentioned previously, IRC M1502.3 says that dryers should be installed and vented according to the manufacturer’s instructions. Each clothes dryer is designed to be vented a certain distance, withstand particular conditions, and operate in a specific manner. Thus, it is important to understand that the dryer manufacturer’s instruction manual takes precedence in terms of installation. Dryer Vent Opening Dimensions According to the IRC Section M1502.3.1, the dryer exit total open area must be at least 12.5 square inches (8065 mm2). This is to ensure that the vent actually allows adequate air exhaustion and ensure proper ventilation. Correct Ducting Material and Size Dryer vents require specific ducting material and a complimentary duct size so that there is a tight fit and no leakage. Both the material and size required to make ducting a successful addendum to soffit dryer ventilation varies based on the dryer and soffit system. However, the IRC does stipulate 3 non-negotiable rules in section M1504.1: Venting ducts require a smooth interior finish. This is important to prevent lint from being caught in the ducts (fire hazard).These ducts must be constructed of metal such as stainless steel and aluminum foil with a thickness no less than 0.0157 inches or 0.3950 mm.The duct must be 4 inches (102 mm) in diameter. No Shared Exhaust Systems A dryer vent and a bathroom fan should never share the same exhaust system. This is stipulated in section M1502.2 of the IRC: “Dryer exhaust systems shall be independent of all systems and shall convey the moisture to the outdoors. Exception: this section shall not apply to listed and labeled condensing (ductless) dryers.” This legality stems partially from the differences between the two ventilation systems. A dryer vent and another ventilation system often have different protocols. For example, dryer ducts cannot use the popular flexi duct that is often used for fans because dryers have more strict cleaning rules for regularity. Thus, if a dryer vent and another ventilation system were combined, there would be material incompatibility because the same type of ducts cannot be used for both ventilation systems and this becomes inefficient to operate. But more importantly, this rule exists because there are significant dangers associated with combining a dryer vent with another exhaust system such as a bathroom fan. For more information, read through my article on Can Bathroom Fan and Dryer Share a Vent. Duct Installation Requirements for Soffit Dryer Vents According to the IRC in section M1502.4.2, Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct. Where dryer exhaust ducts are enclosed in wall or ceiling cavities, such cavities shall allow the installation of the duct without deformation. This is a lot of information, but why are these dimensions important? Supporting the ducts at intervals no greater than 12 ft (3658 mm) helps to prevent sagging of the ducts. Sagging causes pooling of moisture, collection of lint, and just generally interferes with the efficiency of airflow through the duct. The supports also reduce stress on the ductwork, minimizing the risk of breakages over time. Inserting the end of one section of ducting into the adjoining duct, specifically in the direction of the airflow makes the connections much stronger and less likely to interfere with the efficiency of airflow. The reason why screws, etc., must not protrude beyond 1/8 inch or 3.2 mm into the inside of the duct is that these would interfere with the airflow and would act as additional surface areas on which lint could collect. The importance of an undeformed duct is simply to protect its integrity over time and to ensure that the airflow is unimpeded as it carries exhausted air through the soffit. Allowable Length of Ducting Between Dryer and Soffit According to the IRC sections M1502.4.6.1 – M1502.4.6.3, the largest allowed exhaust duct length is determined by the design of the exhaust duct system. Section M1502.4.6.1 states the following: The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. However, for each additional dryer duct exhaust fitting, you decrease this length by a specific amount. You can veiw Table M1502.4.6.1 of the IRC for these reductions. An example is if you add a 4" radius mitered 45-degree elbow to the ductwork, you have to subtract 2 ft and 6" from the maximum allowable duct length. The reason for this is that each additional fitting decreases the airflow efficiency of the ductwork and humid air from the dryer will only be exhausted properly over a shorter distance. Manufacturer directions will, of course, take precedence when it comes to maximum ducting length, but the information above can be used when there are no instructions. Furthermore, you will likely find that the manufacturers adhere to the maximum length of 35 ft with reductions for fittings. No Screens According to IRC M1502.3, screens are not permitted to be installed at the duct termination region. This is because lint will build up on the screen and create a blockage. This lint build-up is not only a hindrance to effective ventilation, but it is also a potential fire hazard. Install a Backdraft Damper While screens are not permitted to be installed, a backdraft damper, such as that pictured above, is required to be installed at the exhaust duct termination region. A backdraft damper is a device that operates with a movable plate made of various materials (metal, plastic). The way the plate is designed in the damper allows air to flow through the exhaust duct to the outside but prevents the outside air (and the exhausted air) from flowing back into the building. This is particularly important for dryers that vent through the soffit because the air is exhausted down as opposed to up (like through a roof vent). Depending on the manufacturer’s instructions, the damper is required to be installed either in a vertical or horizontal orientation. This orientation must also agree with the slats/blades of the exhaust vent. Furthermore, it is essential to understand the direction of airflow before you purchase your damper because general gravity dampers only operate with an up airflow and will not operate with a down airflow, like that which occurs at the soffit vent termination. I recommend AC infinity backdraft dampers. Try to avoid the cheap plastic ones. They are usually not rubber-sealed nor spring-loaded. This means that they will leak cold air into the house and could be noisy when windy. How Do You Install a Soffit Dryer Vent? You can ask an installation/repair person to install a soffit dryer vent into your building for a fee, or you can install it yourself after purchasing the parts required. This activity may take several hours, so it is recommended to set aside an afternoon, or even a full day if you are a novice, for installation. Tools you may needAmazon linkCorded drillLinkDrill bit set compatible with a corded drillLinkTape measureLinkMetal snipsLinkScrewdriver (slotted, Phillips, Square/Roberton, and Torx Aka/Star)LinkCaulk gunLink Materials you may needAmazon linkSoffit vent cap (remember to get one without a screen!)LinkDamperIncluded with vent capDuct cap-Foil tape (aluminum tape is okay)LinkDuct tapeLinkExterior caulkLinkPipe strapsLink4" ducts-4" elbowsLink Identify the shortest and straightest route for the ductwork to the soffit.Purchase the materials you may need (remember to ensure they are IRC-compliant). Purchasing materials specifically designed for dryers will be your safest bet.Ensure the cap sits correctly on the siding by drilling a test hole into the rim joist.Adjust the test hole to fit the siding of the vent cap.Drill the vent hole into the siding with a hole saw.Drill through the rim joist.Insert the vent and screw the cap into the home by pushing the foam backer rod into gaps and caulk.Cut the vent to length with metal snips and wear the correct hand wear (thick gloves).Close the seam on the dryer vent.Tape the elbow joints with the aluminum foil tape.Attach the first vent section and then the remaining sections by sliding the elbows of the vents into the crimped ends.Secure the dryer vents to the walls with pipe straps.Test the dryer vent by turning on the dryer and observing that the vent flap is opening. If not opening, restart from step 1. For more in-depth instructions to install a soffit dryer vent, see this website for step-by-step pictorial descriptions. Below is a helpful video on how to install a soffit vent. https://www.youtube.com/watch?v=JLKFPyq1VJ8 Is the Dundas Jafine Soffit Dryer Vent Really Good When I was researching the best soffit dryer vents, Dundas Jafine all but monopolized the search results. But what makes them so popular? The Dundas Jafine soffit dryer vent is a safe, economical purchase for soffit dryer vents. By searching on their website for “dryer vent”, there are over 24 options for customers to choose from! The vents are made from ultraviolet-resistant plastic which protects the cap from the deleterious effects of the sun, they come with a built-in damper, they can be painted to match the home’s color easily, and they weigh only 2.5 lbs. Consider a Condensing Dryer If, after going through this article, you realize that you are unable to vent through the soffit (as well as unable to vent through the basement and other house outlets), why not consider a condensing dryer? A condensing dryer has an internal system to remove moisture without the need for an external vent. It moves hot air into a condensing chamber where it is cooled, allowing the moisture in the hot air to condensate. This water is then collected and stored in a container below the machine and is emptied out either through a pump system or manually. Benefits of condensing dryers: It can be installed anywhere as it doesn't require ductwork.They are not as invasive as vented dryers and do not require drilling holes into your home. Drawbacks of condensing dryers: They are more expensive compared to vented dryersThey are not as energy-efficient as vented dryers, thus raising the energy bill (although many models come with new heat pump technology with high energy efficiency). Some models do have pumps that empty out the water for you, but some models require someone to manually empty the water from the condenser dryer. Sources https://allurausa.com/blog/what-is-soffit https://dryerbox.com/dryer_venting_guide.htm https://www.thewizway.com/dryer-information-maintenance/benefits-of-a-clean-dryer-vent/ https://homeguides.sfgate.com/dryer-roof-venting-systems-95568.html https://www.conservationmart.com/t-Search.aspx?keywords=backdraft+dampers https://www.familyhandyman.com/project/how-to-install-a-dryer-vent/ https://dundasjafine.com/page/3/?s=dryer+vent https://kitchinsider.com/vented-vs-condenser-tumble-dryers/