There are a lot of rules about “must” and “must not” when it comes to venting a clothes dryer. These regulations exist for good reason, but it makes me think twice about anything to do with the exhaust system.
It’s always a good idea to check when unsure about what’s permitted for dryer ducts. The height seems important since the vent removes exhaust upward, right? However, when you look at the building code, you will find that it isn’t that significant. There are more essential requirements to fulfill.
A dryer vent can be higher than the appliance if the manufacturer doesn’t prohibit it. Venting upwards is fine if it complies with the length, support, and protection for the ducting, and if it terminates outside with appropriate clearances.
Looking at Dryer Vents According to the IRC
The code covers the specifics for ducting and the termination point for the dryer exhaust vent, but it doesn’t mention that the vent cannot be higher than the appliance.
This is likely because it doesn’t make a difference. There are certain aspects of dryer venting that are more important.
What the IRC Does Say About the Run
The IRC gives detailed instructions on the requirements for the dryer ductwork. If any of these are compromised by having the dryer vent higher than the dryer, then this setup should be avoided.
Dryers are meant to be vented to remove heat, lint, moisture, and gaseous by-products (in the case of gas dryers). This is essential to prevent damage to your home and threats to your safety unless you have a listed ventless dryer.
- It mustn’t exceed 35 ft in length—less if there are elbows (Section M1502.4.6.1).
Shorter exhaust duct runs have better airflow and are more efficient. However, elbows change the direction of airflow, which slows it, necessitating the reduction in overall allowable length. To ensure the proper removal of dryer exhaust, the ductwork has specific lengths and dimensions.
- It must be supported at 12 ft intervals or less (Section M1502.4.2).
This is necessary to support the ductwork and prevent damage and warping of the ducts. Any damage to the ducts can compromise the airflow through the exhaust system. Cracked and broken ducts will also allow the exhaust to enter the house, which is highly undesirable.
- The insert ends must align with the direction of airflow (Section M1502.4.2).
Smooth interior duct surfaces are essential to decrease the resistance that slows airflow and encourages lint and condensation accumulation, which impacts safety and efficiency. If the inserts travel in the same direction as the air, it isn’t affected by the ridge of the join.
- None of the ducts can be deformed (Section M1502.4.2).
Ductwork cavities must accommodate ducting without squashing and bending any section of the run. Broken ducting is a health and safety risk and can cause mold growth and structural damage.
- Transition ducts must be a single length, less than 8 ft long, and must be exposed (Section M1502.4.3).
The length of the transition duct is limited to minimize negative impacts on airflow from the ridged interior and the overall length of the duct run. It must also be exposed to prevent compression and damage to the flexible ducting, and you need to be able to see any problems with it.
Manufacturers are the experts on installation for safety and function regarding the appliances they make and the connections you use them with. This is limited to products (and the associated factors) with IRC approval from a safety organization (UL, ANSI, CSA, or ANCE).
Most Dryer Vents Are Higher Than the Dryer
You are unlikely to encounter issues when venting a dryer vertically since there are two factors on your side: the air is hot, and there is a blower.
Hot air naturally rises, meaning it will easily flow upward through the vent. On top of that, you also have the fan that pushes air out of the dryer and helps to send it up the ductwork.
Venting straight through the wall can also be an option, but even where possible, this is rarely the most convenient choice.
Dryers in Basements
If your laundry and dryer happen to be in the basement, you have to vent it upward to get the exhaust outside. There isn’t exactly any other option unless, of course, you have a walkout basement.
When it comes to venting a dryer up from your basement, you need to follow instructions and permissions from the manufacturer where possible. You don’t need to run the ductwork all the way up through the house, just high enough for it to terminate above ground and outside safely.
According to Section G2427.8 of the IRC (venting gas-fuelled appliances, like gas dryers), any appliance that vents through a wall must have at least 12 ft between the bottom of the terminal and the ground. It must also comply with the rest of the dryer exhaust termination requirements and clearances.
Ground clearance is important for vents to ensure they can vent correctly and not become blocked by dirt and snow.
Check your local codes for any amendments to this distance that can come from regional snow lines and other factors.
Ground Floor Dryers
Straight venting is typically not possible, even on the ground floor, as it likely puts the vent terminal near windows, doors, and spaces people walk through or occupy for extended periods.
Some of these locations can also be prohibited by the IRC, Section M1504.3 since an exhaust terminal must be:
- At least 3 ft from any property line.
- At least 3 ft from operational doors and windows, as well as opening for any gravity air intakes.
- At least 10 ft from openings for mechanical air intakes unless the terminal is 3 ft or more above this opening.
These clearances are essential for safety. Dryer exhaust is composed of lint, water, heat, and carbon monoxide (if you have a gas dryer).
Lint is a fire hazard, so it must be removed outside and not be allowed to enter your home through any opening or entrance.
Heat and moisture around or inside your home can cause mold problems, and the damp can damage walls, paint, wood, ceiling boards, grout, etc.
Even though gas dryers produce relatively small amounts, keeping carbon monoxide out of your living space is a priority.
Upper Floor Dryers
You could vent the dryer straight through the wall if it is on an upper floor. This sort of short duct run is highly efficient, however, you need to ensure that you can still maintain the clearances for the vent.
You need to consider windows, soffits and other vents, any chimney, bathroom exhaust terminals, balconies, etc.
If the clearances aren’t possible, you can always vent up through the roof. Just make sure you keep the system independent, so you can’t do something like vent through a chimney.
Venting down through the floor is not prohibited, but it makes little sense in the majority of situations.
Venting Up Through the Roof
Running the dryer vent all the way up through the roof is acceptable (in some cases), but will seldom be the best option for dryers in the basement or even on the ground floor.
The common reason you cannot run the vent for every dryer to the roof is that this is not commonly the shortest route. Dryer ducts need to follow the shortest run to allow the exhaust system to run as efficiently as possible.
The IRC doesn’t exclude venting through a roof. In fact, it doesn’t mention it at all, but if the venting can be done practically with the necessary clearances and a short enough run, there is no reason to avoid the roof. All you need to check is what the manufacturer and your local codes say.