Monitoring the Back Pressure in Your Dryer's Exhaust to Help Prevent Fires and Ensure Best Energy Efficiency
Home Safety

You'll Always Know How Your Dryer is Performing

Back pressure in the dryer's exhaust system is always changing.  Over time, it increases because of lint buildup, crushed hoses, damaged vent hoods and—surprisingly often—animal nests.  The LintAlert® works to protect you by continually monitoring airflow and showing the exact pressure in the exhaust system.  Armed with this information, you can save energy and be certain the dryer is operating at safe levels.

Air Pressure Sensor

The LintAlert gathers this information through a highly discriminating digital pressure sensor. It detects extremely small changes in water column inch (WCI) pressure by sampling minute amounts of airflow. Because of the very small volume of air sampled, there is zero impact to air pressure in the duct.

Onboard Computer

The air pressure samples are then analyzed by a programmable integrated circuit. This small onboard computer evaluates data to know whether the dryer is on and how the exhaust system is performing. Most importantly, it learns each unique system (click here to learn more about computer calibration) so it can compare current airflow to optimal, then report changes over time.

LED Indicators

These changes are shown through a simple to understand LED interface where green indicators, turn to yellow, and then red as pressure becomes more problematic. Optimal performance is shown with a single green indicator glowing. As airflow naturally becomes restricted over time, the second, then third green indicator will illuminate. This is a good time to clean the dryer and duct system for best energy efficiency and safety.  In the event the system is not cleaned at that point, the yellow and red indicators will eventually illuminate. Once pressure becomes dangerous (or there is a sudden obstruction) all LEDs flash in unison and an audio alarm sounds.

Dryer Duct Connection

For the sensor to sample pressure in the system, a self-tapping fitting, the SmartTap™, attaches to the transition hose behind the dryer. This fitting is connected to the alarm module by a 1/8" tube and provides flexibility to plug the alarm module into the nearest power outlet (to conserve available power sources, the LintAlert includes a pass through terminal into which other electronic devices can be plugged).


Alarm Module

Transparent Lens:
Illuminated from behind with three blue LED's. Ready or Stand-By mode is illuminated in blue and is bright enough to provide a soft night-light effect. The Alarm state alternates on and off.
Blockage Indicator:
Displays the level of dryer exhaust pressure in the exhaust conduit.  Also used to display microchip status.


Hose Barb:
Connects alarm module to SmartTap fitting on flex transition hose by way of a 1/8" x 6 foot clear tube (included).
Alarm Module:
The two part case is injection molded in the United States from a special blend of polycarbonate and ABS.  PC-ABS is one of the most widely used industrial thermoplastics and offers the superior mechanical properties and heat resistance of PC and the strength features of ABS.
Thumb Nut:
Used to tighten down and secure the SmartTap fitting.
Dryer Exhaust Connection
Curved Washer: Note air-flow indicator arrows and flattened section of interior diameter.

Felt Washer

Airflow Indicator for Flex Transition Hose Alignment
Flex Transition Hose in relation to the positions of the SmartTap fitting components. (Aluminum semi-rigid type preferred.)

Umbrella portion of SmartTap fitting:
Initially installed from within the flex transition hose. Note that the curved contour should match or align with the interior radius of the flex hose.
Speaker Port:
Audible alarm can be heard
through this port. Alarm sound can
be muted with control button below.




Control Button:
Used initially to calibrate your
specific dryers' pressure
levels and also used test the
unit and mute the audible
alarm once the alert state
is activated.





Pass Through Terminals:
This is a non-switched outlet
providing a convenient plugin
for an iron, washing machine or
other electrical equipment.






SmartTap
Fitting™


LintAlert Dryer Exhaust Monitor

Dryer Exhaust and Knowing When an Alert is Required

Major dryer manufacturers' installation instructions all identify the recommended pressure for an acceptable exhaust system. Pressure can be measured using an inclined manometer or Magnehelic Gauge. The three major appliance manufacturers differ slightly. On average .75 inches of water column pressure is considered to be too high for the equipment to operate safely.

In addition to the appliance manufacturers, the Chimney Sweep Institute of America publishes training manuals for Certified Dryer Exhaust Technicians (C-DET) and states .6 inches of water column (WCI) as being a point where cleaning is necessary.

The paragraph right below is a portion of Frigidaire's® Installation Instructions for Gas & Electric Dryers and states the following Exhaust System Requirements. It is important in that it points out the importance of monitoring pressure levels in the exhaust conduit of the dryer.

Use only 4 inch (10.2 cm) diameter (minimum) rigid or flexible metal duct and approved vent hood which has a swing-out damper(s) that open when the dryer is in operation. When the dryer stops, the dampers automatically close to prevent drafts and the entrance of insects and rodents. To avoid restricting the outlet, maintain a minimum of 12 inches (30.5 cm) clearance between the vent hood and the ground or any other obstruction.

In installations where the exhaust system is not described in the charts, the following method must be used to determine if the exhaust system is acceptable:
  1. Connect an inclined or digital manometer between the dryer and the point the exhaust connects to the dryer.
  2. Set the dryer timer and temperature to air fluff (cool down) and start the dryer.
  3. Read the measurement on the manometer.
  4. The system back pressure MUST NOT be higher than 0.75 inches of water column. If the system back pressure is less than 0.75 inches of water column, the system is acceptable. If the manometer reading is higher than 0.75 inches of water column, the system is too restrictive and the installation is unacceptable.


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Testing Systems for Accurate Lint and Air Restriction Alerts

LintAlerts are regularly lab tested across multiple scenarios. This includes varied exhaust conduit layouts that represent the majority of conditions typically found in residential construction today. This is then combined with the differing mechanical designs of today's clothes dryers which produce many different airflow and back pressure conditions and a broad matrix of analyzable factors.

This testing process is the original driver for the LintAlert's evolution into its current advanced state, and it ensures an accurate understanding of each unique dryer exhaust system. Today, the LintAlert's onboard digital processor is able to determine specific conditions and calculate what incremental change intervals best represent efficiency levels for accurate feedback.

This continuing research and development will likely bring about future releases that address new consumer needs. To date, this vent and lint alert system is known to work on all dryer except those with dual motor technology, inline dryer booster fans, and dryers that share exhaust systems as occasionally found in high-rise structures.

Resources:
Electrolux's Installation Instructions page 7
Frigidaire's Installation Instructions page 3
Samsung Venting Guidelines page 9
Whirlpool Venting Guidelines page 5


Installation Manual
4-Minute Technical Demonstration Video

Alarm Module Detail Close Up
Clogged Dryer Vent Safety Alarm Detail
Easily Tap into Dryer's Exhaust to Monitor Pressure


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