Can a Water Heater Cause Carbon Monoxide?
Carbon monoxide is one of the more serious concerns associated with fuel burning appliances because you cannot see, smell, or taste it. So, can a water heater cause carbon monoxide?
A natural gas or propane water heater can produce carbon monoxide during combustion. Under normal conditions, the water heater burns fuel properly and carries the resulting combustion gases safely outside through its venting system. The danger develops when the appliance isn’t burning correctly or those combustion gases aren’t venting outside as intended.
Electric water heaters work differently. Because they use electric heating elements instead of burning fuel, they do not produce carbon monoxide.
Which Water Heaters Can Produce Carbon Monoxide?
Any water heater that burns fuel produces combustion gases. That includes:
Natural gas tank water heaters
Propane tank water heaters
Natural gas tankless water heaters
Propane tankless water heaters
Certain commercial fuel burning water heating systems
Electric tank and electric tankless water heaters do not burn fuel and therefore don’t create carbon monoxide.That doesn’t mean every gas water heater presents an immediate danger. A properly installed and operating gas water heater is designed to vent combustion gases safely outside.
How Can a Water Heater Cause Carbon Monoxide Problems?
Carbon monoxide concerns generally involve incomplete combustion, damaged equipment, improper installation, or a problem with the venting system.
Blocked or Damaged Venting
A gas water heater needs an unobstructed path to carry combustion gases out of the building.
Problems can develop when a vent is:
Blocked by debris or an animal nest
Disconnected from the water heater
Crushed, corroded, or damaged
Improperly sized
Installed with an incorrect slope
Terminated in an unsuitable location
Altered during remodeling
Shared incorrectly with another appliance
A vent can still appear connected while failing to draft properly. That is why looking at it from across the room isn’t always enough to confirm safe operation.
Insufficient Combustion Air
A fuel burning water heater needs air for combustion. Problems can occur when a water heater is installed in a small or tightly enclosed space without adequate combustion air openings. Storage, insulation, remodeling materials, or later modifications can also obstruct openings that were originally intended to supply air. Closing a water heater inside a new utility closet without evaluating its combustion-air needs can change how the appliance operates.
Backdrafting
Backdrafting occurs when combustion gases that should travel up the vent are pulled back into the home. This can sometimes happen when powerful exhaust equipment creates negative pressure inside the building. Possible contributors include:
Kitchen exhaust hoods
Bathroom exhaust fans
Clothes dryers
Whole-house fans
Fireplaces
Other vented appliances
Major air-sealing or remodeling work
This doesn’t mean turning on a bathroom fan will automatically make a water heater unsafe. It means the complete venting and air supply arrangement needs to work under the conditions that occur inside the home.
Improper Installation
A water heater and its venting must be installed for the appliance, fuel type, location, and available venting system. Potential problems include:
Incorrect vent material
Poorly fitted vent connections
Improper vent sizing
Inadequate combustion air
Incorrect gas pressure
Using the wrong fuel type
Improperly converted equipment
Venting a replacement heater exactly like the old one without confirming compatibility
A new water heater may have different dimensions, input ratings, and venting requirements from the one it replaces.
Burner or Combustion Problems
A dirty, damaged, improperly adjusted, or malfunctioning burner may not burn fuel correctly.
The cause could involve the burner assembly, gas pressure, air supply, internal components, or another condition that requires professional diagnosis. Replacing one component without determining why combustion is abnormal may not correct the underlying problem.
Warning Signs Around a Gas Water Heater
Carbon monoxide itself has no visible appearance or recognizable odor. However, certain conditions around a gas water heater can indicate a combustion or venting problem. Warning signs may include:
A carbon-monoxide alarm sounding
Black soot around the water heater or vent
Scorching or discoloration near the draft hood
A vent connector that is loose or disconnected
Visible damage or corrosion in the vent
Melted plastic near the top of the unit
Unusual condensation or moisture around the vent
Repeated burner or pilot problems
Exhaust odors around the water heater
Symptoms that improve after leaving the building
These signs don’t prove that carbon monoxide is present, and their absence doesn’t guarantee that everything is operating correctly. A functioning carbon monoxide alarm and proper professional testing are much more reliable than trying to judge the appliance by appearance alone.
Can You Smell Carbon Monoxide?
No. Carbon monoxide is colorless and odorless. The rotten egg odor associated with a natural gas or propane leak comes from an odorant added to the fuel. That odor is not carbon monoxide.
A home can have a carbon monoxide problem without smelling like gas. It is also possible to have a fuel leak without a carbon monoxide alarm sounding because the alarm is designed to detect carbon monoxide, not unburned natural gas or propane.
Treat either situation seriously, but understand that they are not the same problem.
What Are the Symptoms of Carbon-Monoxide Exposure?
Common symptoms of carbon-monoxide exposure may include:
Headache
Dizziness
Weakness
Nausea or vomiting
Chest pain
Confusion
Shortness of breath
Unusual sleepiness
Loss of consciousness
The symptoms can resemble the flu, but carbon monoxide exposure generally does not cause a fever. Multiple people feeling ill at the same time or symptoms improving after leaving the building should be taken seriously. Children, older adults, pregnant people, individuals with certain medical conditions, and sleeping occupants may be especially vulnerable.
What Should You Do if a Carbon-Monoxide Alarm Sounds?
Do not assume the alarm is malfunctioning. If a carbon monoxide alarm sounds:
Move everyone, including pets, outside into fresh air.
Call 911 or the fire department from outside.
Follow the instructions provided by emergency personnel.
Do not re-enter until authorities say it is safe.
Have the fuel-burning appliances and venting inspected before returning them to service.
Do not remain inside searching for the source. A carbon monoxide alarm can warn you that CO is present, but it cannot identify which appliance produced it. The source could be the water heater, furnace, fireplace, stove, generator, vehicle, or another fuel burning appliance.
Where Should Carbon Monoxide Alarms Be Installed?
Every home with fuel burning appliances or an attached garage should have functioning carbon monoxide alarms. Placement requirements can vary, so follow:
The alarm manufacturer’s instructions
Current local requirements
Guidance from your fire department
Applicable building and safety standards
Alarms are commonly placed on each level of the home and near sleeping areas. Avoid installing them where steam, extreme temperatures, or other conditions conflict with the manufacturer’s placement instructions. Check the expiration date printed on the alarm. Carbon monoxide alarms don’t last forever, even when the battery is replaced regularly.
Does a Carbon Monoxide Alarm Replace an Inspection?
No. An alarm provides an important warning if carbon monoxide reaches a detectable level, but it doesn’t confirm that the water heater is installed or venting correctly. A professional inspection may include evaluating:
The condition of the vent connector
Vent size and material
Connections and clearances
Combustion-air availability
Burner operation
Signs of soot or incomplete combustion
Draft and spillage
The surrounding appliance area
Changes made since the original installation
The complete system matters. Replacing the water heater without correcting a venting or combustion air problem could leave the underlying condition unresolved.
When Should a Gas Water Heater Be Inspected?
A gas or propane water heater should be evaluated when:
A carbon monoxide alarm has sounded
Soot or scorching appears around the unit
The vent is loose, damaged, or corroded
The water heater has repeated burner or pilot problems
The installation area was remodeled or enclosed
A large exhaust fan was added
Doors, windows, or ventilation openings were changed
The unit was recently installed or relocated
You are unsure whether the existing vent is appropriate
Someone experiences possible CO symptoms inside the building
Fuel burning appliances should also be inspected periodically according to the manufacturer’s instructions and applicable safety guidance.
What About Direct Vent and Power Vent Water Heaters?
Not every gas water heater uses the same venting system.
Atmospheric Vent Water Heaters
A standard atmospheric water heater generally relies on natural draft to carry combustion gases upward through a metal vent. Because it draws combustion air from the surrounding space, the available air and pressure conditions inside the building are important.
Power Vent Water Heaters
A power vent water heater uses a fan to move exhaust gases through approved vent piping.
It requires electricity and must have the correct vent material, routing, termination, and installation.
Direct Vent and Sealed Combustion Water Heaters
Direct vent or sealed combustion equipment typically draws combustion air from outside and vents exhaust directly outdoors. This reduces its dependence on indoor air, but the intake and exhaust still need to remain properly connected, correctly terminated, and unobstructed.
Tankless Water Heaters
Gas tankless water heaters also produce combustion gases. Their venting, air intake, condensate, clearance, and installation requirements depend on the specific model. A tankless unit should never be connected to venting simply because it appears to fit.
Can an Electric Water Heater Set Off a CO Alarm?
An electric water heater cannot produce carbon monoxide because it doesn’t burn fuel.
If a carbon monoxide alarm sounds in a home with an electric water heater, another source must be investigated. Possible sources could include:
A gas furnace
A fireplace
A gas range or oven
A generator
A vehicle in an attached garage
Outdoor equipment operating near the home
Combustion gases entering from an adjoining space
Leave the building and contact emergency services rather than assuming the alarm is defective.
The Bottom Line
A properly installed gas or propane water heater should vent its combustion gases safely outside. Carbon monoxide problems become possible when combustion is incomplete, venting is blocked or damaged, the appliance backdrafts, or the installation doesn’t provide the air and venting the water heater requires.
Electric water heaters do not produce carbon monoxide, but a CO alarm should always be treated as a real warning regardless of which appliances are present.
Hot Water Solutions installs, repairs, and evaluates tank and tankless water heaters throughout Kennesaw and surrounding Metro Atlanta communities.
Call 678-540-6164 if you’re concerned about the condition, combustion, or venting of your water heater.
If a carbon monoxide alarm is currently sounding, leave the building and call 911 before calling a plumber.
Because a cold shower should be by choice.
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FAQ Questions for Rich Results
Can a gas water heater produce carbon monoxide?
Yes. Natural gas and propane water heaters produce combustion gases. A properly operating system vents those gases outside, but damaged venting, incomplete combustion, backdrafting, or improper installation can allow carbon monoxide to become a concern.
Can an electric water heater cause carbon monoxide?
No. An electric water heater uses heating elements and doesn’t burn fuel, so it cannot produce carbon monoxide. If an alarm sounds, leave the building and have other possible sources investigated.
Can you smell carbon monoxide from a water heater?
No. Carbon monoxide is odorless, colorless, and tasteless. A gas odor and carbon monoxide are different hazards, and a home can have carbon monoxide present without smelling like gas.
What should I do if my carbon monoxide alarm sounds?
Move everyone and all pets outside immediately, call 911 or the fire department, and do not re-enter until emergency personnel say it is safe.
What can cause a gas water heater to backdraft?
Possible contributors include blocked or damaged venting, inadequate combustion air, improper installation, and negative pressure created by exhaust fans, dryers, fireplaces, or other equipment.
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