To reset the smoke detector on an HVAC system (usually called a duct smoke detector), locate the detector housing mounted on the return or supply air duct near the HVAC unit. Press and hold the physical Reset button on the unit for 2-3 seconds.
Take the smoke detector off its mounting bracket on the ceiling and disconnect the power cable connected to the smoke detector. Remove its battery, then press the “Test” button and hold it down for 15 seconds. An alarm will sound brief, then the alarm will silence.
Code Compliance and Regulations
NFPA 90A (Standard for the Installation of Air-Conditioning and Ventilating Systems): Mandates smoke detectors in HVAC systems exceeding 2,000 CFM (Cubic Feet per Minute) and in systems serving multiple floors.
Hardwired Smoke Alarms
Each breaker should be labeled, so look for something that says “smoke alarm” or something similar. Turn off the circuit breaker for your smoke alarms. If your smoke alarms don't have battery backup, doing that will turn all of them off.
For hardwired units, a steady green LED light indicates that the alarm is receiving AC power. Battery-operated units will have a quick flash every 30-45 seconds. However, this does not necessarily mean the alarm is working. Pressing the Test button is the only recommended method to ensure functionality.
If the smoke is not too dense, the alarm will silence immediately. If the smoke or debris is interfering with the sensor, the alarm will override the Hush. The smoke alarm will automatically reset after approximately 8 minutes unless particles of combustion are still present.
In hardwired smoke alarms, disconnecting the unit typically triggers a trouble signal on the main panel, not a full alarm. The chirping every 30 seconds usually indicates a low backup battery. Replace the 9V or lithium battery first.
To do that, remove the battery from the unit and hold the reset/test button for 15-30 seconds. It may make a sound when you push that button, especially if it also hardwired, but do not panic, it will shut off quickly.
Protection of HVAC systems and property
Duct smoke detectors safeguard HVAC systems and property by quickly identifying smoke before it spreads through ductwork. These essential devices prevent fire damage and protect occupants by triggering alarms and shutting down air handling units.
Detecting HVAC Leaks
Usually there are openings large enough to admit a pail or similar non-flammable container with a smoke candle in the system. We suggest introducing smoke twice the volume of the area being tested.
All smoke alarms (including hard-wired or those with removable batteries) should be replaced after 10 years, or by the replace by date on the base or earlier if they are found to be defective. The sensor in a smoke alarm can degrade over time.
Ducted air conditioning and heating systems must shutdown automatically upon the activation of the fire alarm. This requirement is intended to capture systems which comprise of a central unit with ducting to multiple rooms within the house, for heating or cooling, etc.
Simply press and hold the test/hush button for 10–15 seconds. Wait for the alarm to stop sounding and test it again to confirm reset.
How to Reset a Smoke Alarm
To reset, please hold down the test button for about 15 seconds. You will hear an alarm sound for a short time, and then it will go silent. Once that is done, install the new battery. You can then proceed and connect the detector back to the power supply and back to the mounting brackets.
Most home alarms will automatically rese between 7-15 min. These are generally 120v units with battery backup. In a commercial fire alarm I.E an apartment building the in unit smoke/co detectors are programmed as a supervisory with auto reset. They will clear once the condition is gone with no set time limit.
If your smoke alarm keeps going off, try these steps in order:
It's a sound many homeowners have heard: the 3 a.m. alarm chirp. Why does it happen? Well, it's a simple matter of the battery's charge level and a home's air temperature. As a smoke alarm's battery nears the end of its life, the amount of power it produces causes an internal resistance.
To help you better understand how smoke alarms work, here are the top causes of smoke detector false alarms.