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Smoke on the Water Heater | Stop Heater-Triggered Alarms

While researching a fix for a smoke detector of mine that kept nuisance tripping, I came across multiple articles in which firefighters and other safety professionals said that people don’t take fire safety seriously enough. There were numerous examples of serious fires that could have been averted by timely smoke alarms. 

The reason why smoke alarms didn’t go off in those cases? Folks had either disabled them or uninstalled them, because they kept nuisance tripping – in other words, giving out false alarms!

Coming back to my smoke detector, I discovered that it was being triggered by my water heater. The smoke detector was located in the hallway right outside the water heater closet, and would go off if someone opened the closet door when the unit had been running a while. I solved the problem by relocating the alarm to the other end of the hallway.

So, how does a water heater set off a smoke alarm? Which type of smoke alarm is best around water heaters? What can you do to prevent nuisance tripping?

Read on to find out!

A common trigger for household smoke detectors is the presence of water vapor generated by activities like cooking and showering. Domestic HVAC systems and water heaters can additionally trigger smoke alarms as they release significant amounts of heat and moisture into the surrounding air.

Why Water Heaters Set off Smoke Alarms: ‘A Fit of the Vapors’

If you’ve been dealing with smoke alarms at home, you probably know that the two most popular kinds use either ionization chambers or photoelectric sensors; they’re commonly known simply as ‘ionization alarms’ and ‘photoelectric alarms’. Ionization units are cheaper, costing only about half as much as the photoelectric models.

So, how could a water heater set off a smoke alarm?

Ionization alarms work by detecting disturbances in an ionization field. When smoke particles enter the ionization field, they disrupt the flow of ions, and this triggers an alarm.

Photoelectric alarms work by detecting reflected light. When smoke particles come into the ray of light emitted by the device, they reflect this light onto a sensor located at the opposite end, which triggers an alarm.

In practice, both types of alarms can be triggered by things other than smoke particles. And one of the most common ‘culprits’ that can trigger false alarms is water vapor. For instance, steam billowing out of a shower cubicle or rising from a cooking pot can set off a smoke alarm. 

Similarly, the elevated temperature of an operating water heater is enough to heat the surrounding air and create significant amounts of humidity. This could potentially trigger a smoke alarm, especially when the unit is located in a poorly ventilated basement, closet or crawl space where humid air can build up.

To minimize the likelihood of nuisance tripping (false alarms), ionization and photoelectric type smoke detectors must ideally be positioned 20 feet away from water heaters, especially units located in poorly ventilated basements, closets or crawl spaces that have high levels of humidity / dust.

(If you’re considering moving your electric water heater to a new location, check out this helpful guide on water heater wiring.)

Which Type of Smoke Alarm Works Best Around Water Heaters?

Data shows that false alarms due to high levels of humidity / dust, are three times as likely in ionization alarms as photoelectric alarms. However, photoelectric alarms are more prone to be triggered by insects crawling into them, or by dust motes generated by propane / natural gas water heaters.1

Besides the issue of nuisance triggering, there’s also the very real concern of fire safety. Which type of alarm would be better at signaling a water heater fire?

Again, the answer is, it depends.

Research shows that photoelectric alarms do well in detecting smoldering fires like those caused by faulty wires and short-circuits (e.g., in electric water heaters). However, ionization alarms are faster to detect rapid, flaming fires due to flammable materials, a risk higher in gas water heaters.2

One solution is to use ‘dual sensor’ alarms that include both ionization and photoelectric devices. Of course, these come at a cost. 

Some alarms use gas sensors, detecting high levels of Carbon Monoxide (CO), a toxic by-product of smoldering fires. Being immune to dust and water vapor, a CO alarm is less easily nuisance triggered, but it would be ineffective in signaling a rapid, flaming fire, for instance, resulting from a gas water heater. 

A third kind of alarm that’s being increasingly used in basements and garages uses a heat sensor, which detects ‘rate of rise’, that is, how quickly temperature is rising in that area. The drawback is that a heat sensor might not signal a fire quickly enough to prevent property damage, especially in case of a smoldering fire such as a water heater short-circuit might produce.

In view of the greater risk of injury and higher death rates associated with smoldering fires, the International Association of Fire Fighters (IAFF) has officially declared photoelectric alarms to be mandatory in certifying a house as having adequate fire safety.

However, there is no legislation against home-owners installing additional alarms (ionization, gas, etc.) as added precautions.

How Can I Prevent Nuisance Tripping?

Short of blowing a pile of $$$ on a fancy suite of alarms, is there anything you can do to prevent nuisance tripping and false alarms, while ensuring that your home has fire safety?

The good news is, yes, you can!

By taking a few simple precautions, you can ensure that you and your loved ones have a working fire safety system that doesn’t go off for no reason at the most inconvenient times. Follow the steps below to maximize your odds of a peaceful, hassle-free home smoke alarm system.

1. Positioning

Make sure that smoke alarms are positioned well away from sources of heat and humidity, like stoves, water heaters, furnaces and shower cubicles. For more information on the ideal positioning of smoke alarms, watch the video below.

2. Maintenance

Keep your home’s smoke alarms functioning well by ensuring that:

  • They are cleaned regularly of dust and grime by vacuuming gently with a soft brush. If cleaning by hand, use a soft-bristled paint brush.
  • Replacing the batteries regularly. Remember that nuisance tripping is often because of low batteries that cause sensors to malfunction.
  • Installing new smoke detectors every ten years to replace old ones.

3. Precautions

Although it may be tempting to disable a smoke detector to avoid nuisance tripping, remember that these devices could potentially save your life (and those of your loved ones), as well as your valuable property.

According to the National Fire Protection Association (NFPA), one in ten home heating fires is caused by a malfunctioning water heater.3 Keep yourself and your home safe – make sure your smoke alarm system is functioning!

You now know set up your appliances and smoke alarms such that you won’t have to deal with routine nuisance tripping.


  1. Mueller, B. A., Sidman, E. A., Alter, H., Perkins, R., & Grossman, D. C. (2008). Randomized controlled trial of ionization and photoelectric smoke alarm functionality. Injury Prevention, 14, 80-86. DOI:
  2. Milarcik, E. L., Olenick, S. M., & Roby, R. J. (2008). A relative time analysis of the performance of residential smoke detection technologies. Fire Technology, 44, 337-349. DOI:
  3. National Fire Protection Association. 2021. NFPA urges added caution when using home heating equipment, the leading cause of US home fires between December and February.

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