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Updated: Mar 2, 2023

Back drafting is dangerous when toxic combustion gases are not adequately ventilated. Instead of rising through the flue and releasing the gases outside, some of the exhaust gases enter the home, as this video depicts.

If left untreated, it can create an environment of carbon monoxide poisoning. Why does this happen? Why does this happen?

In our experience, this happens for one of three reasons:

  • The vent was incorrectly installed. The vent pipe has too many angles or a downward slope.

  • There can be a blockage in the vent or

  • The furnace shared the vent, and when the homeowner replaced their furnace with a more efficient one, the BTU produced from the orphaned water heater was not enough to drive the gases out of the home.

How can you tell if back drafting is occurring?

  • Inspect the draft hood for soot.

  • The plastic caps on the water heater are melted or deformed.

You see corrosive stains on the top of the water heater.

What should you do if your home inspector or you find signs of back drafting?

Immediately improve the ventilation in your home by opening the windows or running the nearby exhaust fan from the bathroom or kitchen.

Next, call an experienced HVAC company to look at your water heater and see what can be done to remedy the situation.

Replace the vent cap or install a power vent.

Lastly, depending on the age of the water heater, consider replacing it with a power venting unit with a fan to push gases outside of the home.

Key Takeaway and Final Thoughts

“Melted plastic rings on top of the water heater may indicate that the combustion gases from the water heater are back-drafting into the home. Other evidence would be soot or corrosion. If you notice any of these indicators, you need to have the flue inspected by a Heating, Venting, and Air Conditioning (HVAC) company to make sure that the flue is the proper size for the equipment and that the flue is not blocked with debris such as a bird’s nest,” stated Dave Christopher, owner of Integrity Home Evaluation Services.
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