Should I Smell Propane from My Tankless Water Heater Exhaust?

No, you should not smell propane from your tankless water heater exhaust. Propane is a fuel used in many water heaters, and it should be completely burned during the combustion process. If there is unburnt propane in the exhaust, it could indicate a problem with the combustion process, such as incomplete combustion or a blocked vent pipe.

Causes of Propane or Exhaust Fumes from a Tankless Water Heater

According to the search results, there are several potential causes of smelling propane or exhaust fumes from a tankless water heater:

  1. Improper Combustion: Improper combustion can result in the production of aldehyde odors. This can be caused by a lack of fresh air for the exhaust, which can lead to incomplete combustion and the production of harmful fumes.

  2. Blocked Vent Pipe: A blocked vent pipe can prevent the exhaust from being properly expelled outside, leading to the accumulation of fumes.

  3. Propane Leaks: Leaks in the propane line can cause the smell of raw gas to be present in the exhaust.

  4. Malfunctioning Burner: A malfunctioning burner can also lead to incomplete combustion and the production of fumes.

  5. Insufficient Airflow: Insufficient airflow to the tankless water heater can cause the combustion process to be disrupted, leading to the production of fumes.

Diagnosing the Problem

should i smell propane from my tankless water heater exhaust

If you suspect that there is a problem with your tankless water heater, it is important to take action immediately. According to the Plumbing Forum, raw gas coming from the exhaust pipe is a serious issue that should be addressed by a qualified technician as soon as possible. Similarly, the Love Plumbing & Remodel forum advises that if you detect any odors from the exhaust, you should call your gas company or a qualified technician to investigate the issue.

To diagnose the problem, you can perform a simple test by spraying soapy water around the connections in the propane line at the water heater to check for leaks. However, if you are not comfortable performing this test or if you suspect that the problem is more serious, it is best to call a qualified technician.

Potential Consequences of Ignoring the Problem

Ignoring the problem of propane or exhaust fumes from your tankless water heater can have serious consequences, including:

  • Fire Hazard: Unburnt propane in the exhaust can be a fire hazard, as it can ignite and cause a fire.
  • Carbon Monoxide Poisoning: Incomplete combustion can lead to the production of carbon monoxide, which is a highly toxic gas that can cause illness or even death if inhaled.
  • Damage to the Water Heater: Continued use of a tankless water heater with a problem in the combustion or venting system can lead to damage to the water heater itself, requiring costly repairs or replacement.

Preventive Measures

To prevent the issue of propane or exhaust fumes from your tankless water heater, it is important to:

  1. Ensure Proper Ventilation: Make sure that the tankless water heater is installed in a well-ventilated area with adequate airflow to support the combustion process.
  2. Regularly Inspect the Vent Pipe: Regularly inspect the vent pipe for any blockages or obstructions that could prevent the proper expulsion of exhaust.
  3. Schedule Regular Maintenance: Schedule regular maintenance with a qualified technician to ensure that the tankless water heater is operating at peak efficiency and to identify any potential issues before they become serious.


In summary, you should not smell propane from your tankless water heater exhaust. If you do, it could indicate a serious problem with the combustion process or the venting system. To diagnose and fix the problem, it is best to call a qualified technician immediately. Ignoring the issue can have serious consequences, including fire hazards and carbon monoxide poisoning. By taking preventive measures and scheduling regular maintenance, you can help ensure the safe and efficient operation of your tankless water heater.

Plumbing Forum
Love Plumbing & Remodel Forum
DIY Stack Exchange Forum
Reddit r/HomeImprovement