Common Dryer Venting Problems
During everyday use, lint bypasses the appliance’s filter screen and ultimately accumulates in the duct. Knowing the dryer has to breathe well to move the hot air outside, any increase in restriction – or back pressure – fuels the potential of a dryer fire. As back pressure goes up, lint is actually forced back towards the appliance, then piles up on the wiring and heating element which could ignite into a dryer fire.
Six common factors contribute to dryer fires, but often times they are hidden.
Even without knowing how much lint buildup exists inside the duct work, you can still do some basic visual inspections to determine if your venting system has issues that can be improved. If you experience or see any of the following issues, consider professional dryer vent cleaning along with a LintAlert to maximize your safety and efficiency.
- Clothes are coming out of the dryer very hot after a cycle
- The laundry room is warmer than usual when the dryer is on
- Drying cycle times have increased
- Lint is building up behind and around the dryer
- Lint is visible at the wall or roof termination point
- Screen-like features are visible at the exterior termination point
- The transition hose is coiled around and/or crushed behind the dryer
If any of these factors are visible, contact your local duct company or appliance repair crew. For DIY homeowners, specialized dryer vent cleaning tools are available as well.
The Importance of Performance
In an effort to maximize dryer venting safety and efficiency, HVAC service professionals used specialized testing tools to measure the dryer’s ability to safety vent warm, moist air to the outside. Two common tests include measuring airflow velocity and determining back pressure levels. By testing dryer vent performance, you can determine what (if any) improvements can be made to save on utility costs, shorten cycle times, and lengthen the life of your appliance.
What is Back Pressure?
Back pressure, or airflow resistance, play a key role in dryer venting. Appliance manufactures along with industry standards feel a dryer vent with over 0.6 – 0.8 water column inches (wci) of pressure is considered blocked or restrictive. High back pressure readings put a strain on the appliance and can shorten the dryer’s life span, create longer cycle times, and increase the wear and tear on your clothes. Back pressure can be read with a Magnehelic Gauge, Digital Anemometer, and even your LintAlert PRO Plus.
Getting a good back pressure reading (< 0.8 wci) does not always mean the system is clean from end to end. It’s possible the dryer vent has a leak or disconnect somewhere in the run so it’s recommended to check the airflow velocity too. A concealed broken duct may be exhausting inside the house which means little to now airflow will be measured at the exterior termination point. Therefore, it’s highly recommended to check both the back pressure and airflow velocity to test the system’s performance as best as possible.
Understanding Variables with Airflow Velocity
Airflow velocity, or the speed in which air moves from the dryer to the outside, is usually read in cubic feet per minute (CFM) or feet per minute (FPM). Airflow tests should be done behind the dryer as well as the exterior termination point. A dryer vent with good airflow should push 1,500 fpm, or around 8 meters a second. Readings less than 1,500 fpm could indicate some type of blockage or restriction in the exhaust run. A vane anemometer is required to test airflow velocity readings.
A great way to understand airflow velocity readings is to compare the air moving in a duct system to how water moves through a normal 25’ garden hose.
- With no kinks in the hose and not being pinched at the exit point, water comes out at a normal steady rate.
- With a kink half way through the hose and the exit point is open, water will likely come out with less velocity.
- With no kinks in the hose and a restricted exit point, water is forced out faster like a pressure washer.
This example demonstrates that measuring only airflow velocity is not the best way to fully test and diagnose performance issues.
The “best case scenario” is combining airflow velocity tests with back pressure readings as their relationship is symbiotic. Higher back pressure readings should yield lower airflow velocity readings. And in turn, lower back pressure readings traditionally have higher airflow velocity.
The NADCA Dryer Exhaust Duct Performance (DEDP) Standard
The National Air Duct Cleaning Association introduced a new standard in 2015 focused on testing residential exhaust duct performance called the Dryer Exhaust Duct Performance Standard, or DEDP. This Standard advocates that service professionals and property managers have each residential dryer vent run tested for performance parameters. The DEDP Standard’s foundation is based on measuring back pressure and airflow velocity. This Standard further validates the importance to maintain a safe and efficient duct run and helps identify jobs that require professional duct cleaning and/or duct work improvements. Click to download the DEDP Standard (PDF)
Monitor Performance with Your LintAlert PRO Plus
The LintAlert is essentially a homeowner’s simple version of a Magnehelic Gauge (and so much more!) The device itself has 5 LEDs that progressively show an increase in pressure, just like the professional HVAC tools. Also, the app interface provides you with these HVAC tools (over $200 in value) so you can monitor performance at any time in the palm of your hand. Once connected, you can stay protected.
5 Benefits of a Clean Dryer Duct Run
Maintaining a clean and efficient dryer vent has numerous consumer benefits. First, shorter cycle times let you process more laundry loads quicker. The less you need to run your dryer, the longer your appliance will operate normally. By running the dryer less, you’ll see a direct savings in utility rates. (Note – a blocked dryer vent system could cost an average household over $200 more each year compared to the same system that’s cleaned regularly.) Clothes get abused each time they are placed in the dryer, so shorter cycles times lessen the wear and tear on your clothes. Lastly, and perhaps most importantly, maintaining a clean duct run decreases your risks of having a dryer fire.