GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

CO2 emissions from a vent free propane fire place

jtrevenew | Posted in General Questions on

I have owned a house with natural gas vented logs and didn’t have any issues burning those logs when the electricity went out.

I am now renting a house with vent free propane logs. I couldn’t believe it when I saw the metal plate where the fire place venting to the outside normally exists. The propane gas tank installer explained the new vent free logs to me and assured me that it was completely safe.

I tried running the logs for an hour two weeks ago. The logs are in the living room on the 1st floor. The fumes in the second floor spare bathroom were so strong, I turned off the fire place logs and purchased an expensive CO2 detector online with a LCD read out.

I tried to run the logs for another hour this past Saturday. When the CO2 levels were approaching 3800 in the spare bath on the second floor of the house after running the logs for an hour, I cut the logs off. Since OSHA states the levels are not dangerous until the CO2 reaches 5000 ppm, I didn’t quickly ventilate the house, plus I was in a rush to get ready to run errands.

After spending approximately 30 minutes on the second floor (on the other side of the house where the fumes weren’t as strong), I started feeling sick to my stomach and shaky like I had not eaten anything all day. But I just had breakfast just two hours prior. I didn’t immediately connect the sick shaky feeling with the gas fumes. But shortly after leaving the house to run errands and getting into fresh air, the symptoms went away.

Is there something wrong with how the gas logs are operating? Should I be getting CO2 readings above 3800 when running the logs? This house is only 2 years old and seems really tight. What really surprised me, when I turned on the exhaust fan in the spare bathroom on the second floor where the CO2 levels were getting so high, running the exhaust fan made no difference. The CO2 levels just kept going up.

Short of opening windows to the outside of the house (which defeats the purpose of heating the house with the logs…), is there anything I can do to reduce the amount of CO2 building up in the house when running the logs? No prior tenants used the logs, so two years after the house was built, this is the first time these logs are being used.

Thank you for your time!


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Jon_R | | #1

    IMO, the vent free logs are just a bad idea and shouldn't be used. For reasons not limited to CO2.

  2. jtrevenew | | #2

    Thank you for your feedback Jon R. I was of the same impression as soon as I saw the metal plate and no vent opening in the fire place. I even said to the propone gas tank installer - "burning propone inside a building without any ventilation just doesn't sound like a good idea to me......". Of course, they want to sell propane so he wasn't going to say anything negative about it.... :)

  3. GBA Editor
    Martin Holladay | | #3

    Unvented gas appliances are a bad idea. For more information on this topic, see these two articles:

    Avoid Unvented Gas Heaters

    A Ventless Gas Fireplace Doesn’t Belong in Your Home

  4. seiyafan | | #4

    Once the amount of oxygen is not sufficient to support complete combustion, you gonna have CO instead of CO2.

  5. STEPHEN SHEEHY | | #5

    Not to mention all the water vapor created when burning propane. Just because it's legal in some places doesn't mean unvented gas heaters are a good idea.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |