Can a Water Heater Cause a Fire?

water heater

Water heaters are a necessary part of every home. Without them, you wouldn’t be able to take hot showers, run your dishwasher, and perform other essential tasks that require hot water. However, as with all machinery, you’re probably concerned about the fire risks that come with this piece of equipment. 

So, can a water heater cause a fire? Yes, a water heater can cause a fire. Proper maintenance and safety precautions can drastically decrease the risk of a fire. Don’t store flammable materials or liquids near a gas water heater.

There are many nuances and differences between different types of water heaters when it comes to fire safety. This article will discuss these differences, as well as the safety measures you can take to protect your family and home from a water heater fire. 

Fire Dangers: Gas vs. Electric Water Heaters 

While gas water heaters and electric water heaters have entirely different energy sources, their internal workings are similar. Both heat water using their respective energy sources and release that water into your home’s plumbing system

Despite their similarities, the two are not equal when it comes to fire safety. Gas water heaters are significantly more likely to cause a fire than electric water heaters are.

There is one significant reason for this: gas water heaters use natural or propane gas to heat water, while electric water heaters don’t. Electric water heaters are more prone to electrical fires.

The leading cause of gas water heater fires is when they leak flammable vapors into the room surrounding the equipment. If this gas leakage goes on for a long enough time, a dangerous amount of gas can collect and pool near the water heater or other nearby electrical devices. This can trigger an explosion if the vapor comes into contact with the water heater’s ignition flame or electricity. 

The risk of a vapor-caused explosion is much lower in newer gas water heaters than in older models. This is because newer heaters have a sealed bottom, which protects the ignition flame at the bottom of the heater from any gas lurking outside. Many older heaters do not have this sealed bottom, which means a sustained gas leak creates an increased risk of explosion. 

Because electric water heaters don’t use combustible gas, they have a much lower risk of catching fire. Even if a gas leak from another appliance were to surround your electric heater with combustible vapor, there wouldn’t be an ignition flame for the gas to interact with. For this reason alone, an electric heater is probably the way to go if fire safety is a significant concern. 

Can Tankless Water Heaters Catch Fire?

The debate over whether tank water heaters or tankless water heaters are better has been raging for years. Differences in initial cost, maintenance cost, longevity, and hot water supply have created strong arguments for both heater types. 

Tankless water heaters can catch fire, however, the risk is minimal. Tankless water heaters only ignite and heat water on demand. Fire risk with tankless water heaters is largely caused by gas leaks that develop. Electrical sparks near gas leaks could cause fire or explosion.

Tankless water heaters also have built-in safety features that will shut the unit down if a problem is detected. If you have no hot water and hear an audible beeping sound from your tankless water heater, an error exists that will need to be corrected.

Some tankless water heater setups do have an expansion tank that can cause pressure to build up inside the storage tank.

However, when it comes to fire safety, there’s no comparison. Tank water heaters pose a greater fire risk than their tankless counterparts. The reason for this lies in the water pressure that builds up in tank systems.

When the water in a tank heats up, its volume expands, and pressure rises inside the tank. If this pressure is not released somehow, it will eventually become too much for the tank to handle, and it will explode. 

While this sounds scary, you shouldn’t worry too much. Tank explosions are sporadic because most water heater tanks have multiple safeguards to relieve water pressure before it reaches a critical level. 

The first safeguard against explosion is the temperature and pressure relief valve, known as T&P Valve. This valve is typically located at the top of the tank, and its job is to release water when pressure levels reach a dangerous threshold.

It accomplishes this by temporarily opening a small hole in the tank that water can flow out of, thereby lowering the water volume and overall pressure level in the tank. 

The second safeguard is an automatic heating shutoff mechanism. When the heater detects pressure levels are getting too high, it can turn off the heating process and stop pressure levels from climbing too high. These are more common on newer models than older ones, so there’s a chance you’ll be relying solely on a T&P valve to protect you from a pressure-induced explosion.  

Tankless heaters don’t have tanks to build up pressure in, so they don’t have the risk of a pressure-induced explosion. However, that doesn’t mean all tankless heaters are entirely safe. Tankless gas heaters can emit combustible vapors, so you’ll still need to be cautious about that type of fire hazard. 

Safety Measures with Water Heaters

With all this talk of explosive vapors and exploding tanks, you’re probably wondering what you can do to prevent a catastrophic water heater fire. Fortunately, you can take quite a few safety precautions to decrease your risk of a fire or explosion. If you methodically work through each item in this list, your risk of a water heater fire will be astronomically low. 

Schedule a yearly maintenance check

The best way to ensure your water heater is safe is to get a plumber to inspect it annually. While checking the water heater yourself is better than ignoring it, a professional plumber will inevitably catch problems your untrained eye might miss. You are scheduling tankless water heater maintenance or water heater maintenance should be enough to catch minor issues before they become dangerous. 

Test your T&P valve regularly

If you have a tank heater, you’ll want to inspect your T&P valve every couple of months to ensure it’s operating correctly. Here’s a quick guide to checking that your T&P valve is working as expected:

  • Locate the T&P valve. If you’re not sure where to find the T&P valve, take a look at over article Leaky Water Heater Pressure Relief Valve: DIY Guide w/Pics
  • Put on some closed-toed shoes. You’re going to be releasing some potentially scalding water near your feet, so you’ll want to protect yourself as much as possible. 
  • Slide a bucket under the T&P valve’s discharge tube. 
  • Flip-up the valve switch and hold it for approximately five seconds before letting go. 
  • If water comes out of the discharge tube, your T&P valve is working correctly. 
  • If water does not come out of the tube or water leaks from the valve, you’ve got a problem. Call your plumber and schedule a repair as soon as possible. 

Inspect your anode rod every two years

Tank water heaters are typically made out of steel, which means they are at risk of rusting. Your tank heater has an anode rod, a small metal cylinder that protects your tank from rusting. Some people call it a “sacrificial” rod because it sacrifices itself to save your tank from irreversible corrosion. 

While the anode rod is intact, your tank should be safe from rusting. But if the anode rod corrodes completely, the water will start rusting the inner tank. While a corroded tank isn’t a fire risk, the tank could fail to result in a water heater explosion

Set a lower water temperature

A higher water temperature can lead to a higher level of pressure in your water tank. This shouldn’t be an issue if the pressure relief mechanisms on your heater are functioning correctly, but lowering the water temperature can provide some temporary relief if your T&P valve is malfunctioning. 

Clear your water heater room of flammable substances

If you have a gas water heater, you should take every precaution you can to prevent a fire. This includes removing all flammable substances from the room your water heater is in. Here’s a quick list of the most common flammable items you might have stored near your heater:

  • Paint canisters
  • Gasoline canisters
  • Cardboard boxes
  • Stacks of paper or fabric
  • Old wooden furniture

If any of these items are stored in the same room as your water heater, you should move them to another room or get rid of them entirely. 

Make sure the heater is vented correctly

This is another tip for gas heater owners. Your gas heater’s ventilation system must be installed appropriately. Any flaws in the vent duct’s design or installation can cause a dangerous gas leak, which increases the risk of a water heater fire or carbon monoxide poisoning. 

Leave the installation and repairs to the plumbers

A DIY approach to water heater maintenance can save you a lot of money, but water heater repairs are best left to professionals. Because an improperly repaired water heater can have disastrous consequences, the smart move would be to call a plumber whenever you detect a problem with your water heater. 

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Hubert Miles

I've been conducting professional home inspections since 2002. I'm a licensed Home Inspector, Certified Professional Inspector (CPI), Certified Master Inspector (CMI), and FHA 203k Consultant. I started to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
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