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Unvented Gas Appliance Industry Falls Flat at ASHRAE Meeting

Gas Log Fireplace

Unvented combustion appliances were added to the scope of ASHRAE’s residential ventilation and IAQ standard (Std. 62.2) recently. The committee has begun their deliberations on the issue, and at ASHRAE’s winter meeting in Orlando this month, the unvented gas appliance industry folks attempted a defense of their products. Based on the results they presented and the reaction from most committee members, I’d say they failed.

Water vapor and carbon dioxide

The 62.2 committee opened their meeting on Friday with a presentation on the results of a study paid for by the unvented gas appliance industry. They hired a toxicologist named Dr. Gary Whitmyre to do a modeling study to see how operating unvented gas appliances in a home can affect the relative humidity and carbon dioxide levels.

He may have looked at other combustion products as well, but I came in late and didn’t see all the slides. The water vapor and CO2 results, however, provided plenty of reason for caution.

The effect of unvented gas appliances on relative humidity in this modeling study was that the worst 10% of homes could have RH high enough to create significant moisture and mold problems. The worst 1% likely would be “mold disasters” as one committee member put it.


The study also showed that unvented gas appliances would add about 2,000 parts per million (ppm) of carbon dioxide to the indoor air. Note that this is what is added to the existing CO2 level, not what the total would be. Current thinking is that indoor CO2 levels should be limited to 1,000 – 1,200 ppm,  so if a home with unvented gas appliances is already at say 1,000 ppm, the occupants could easily be breathing 3,000 ppm while the unvented gas appliance is running. The result could be drowsiness and impaired cognitive function.

Committee discussion

The ASHRAE 62.2 committee raised a lot of questions about the study. The unvented gas appliance industry folks who sponsored the study certainly didn’t help their cause. One committee member said, “The result of yesterday’s presentation is that I’m more concerned about unvented appliances than I was before I got here.”

On Saturday, they also voted on a proposal to adopt the following language into the residential ventilation standard:

Unvented combustion appliances except for cooking appliances covered in Section 5.1 shall be prohibited.

After discussing it, the vote was 7 in favor, 10 opposed, and 2 abstaining, so the motion failed. But it was close, and the only reason it didn’t pass is that some members feel the committee hasn’t really seen enough data yet.

After more discussion on a different proposal, a committee member proposed that homes with unvented gas appliances have to supplement their ventilation rate by 1 cubic foot per minute (cfm) per 1,000 BTU/hr of appliance capacity. That proposal was referred to a subcommittee so they can discuss whether that’s the right number or not, but there seems to be support for something like that.

In other words, the unvented gas appliance industry would be handing off the cost for venting to the builder, who would have to add more ventilation to the home. Of course, they could just switch to vented appliances.

The prevailing opinion in the broader community

The representatives of the unvented gas appliance industry like to be dramatic. During the discussion of the proposal to prohibit them, one said that if the motion passed they might as well not continue on with the research project they were discussing because “there won’t be an industry left when it’s done.”

Well, there will certainly be a gas appliance left. All those fireplaces will be vented, though, as they should be. The truth is that unvented combustion appliances don’t belong in homes. (Yes, a gas range and oven is technically unvented, but the 62.2 standard requires a ventilation hood be installed there.)

There’s good reason that unvented combustion appliances are banned in homes in Canada and California as well as green building programs. Even when they’re operating properly, the water vapor and CO2 added to the indoor air can create problems.

“No professional I know would recommend an unvented device,” said Robert Bean. I’m with him.


Related Articles

Bob Vila and the Vent-Free Gas Fireplace — A Sorry State of Affairs

Unvented Natural Gas Space Heaters Should Be Removed

A Ventless Gas Fireplace Is a Liability


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This Post Has 32 Comments

  1. I heat most of my house with
    I heat most of my house with two small Rinnai ventless heaters (under 10K btu each). I am most concerned about the emissions and so I test them often with a Testo combustion anaylizer and they never go above 1 PPM CO2. I was quite surprised that they did indeed burn that clean (advertised as 99.9%). Am I missing something here or did the ASHRAE’s residential ventilation and IAQ standard (Std. 62.2) only test other brands?

    1. Terry, are you sure you don’t
      Terry, are you sure you don’t mean 1 ppm of CO, not CO2? The 2 products of the complete combustion of methane (which is the main component of natural gas) are carbon dioxide and water vapor. I wouldn’t think it’s possible for them to produce only 1 ppm, but I could be wrong.

      The issue for the 62.2 committee, though, is not how well the best units do but how they perform in a wide variety of conditions.

      1. Allison – you are right re.
        Allison – you are right re. CO2 readings, they should be higher. So now about CO.
        Even if you get an acceptable CO reading – how confident are you about the accuracy of your CO tester? How can you be sure the appliance combustion will not go sideways? (many reasons for this – I will write an article about this soon). The whole idea of gas-fired, unvented appliances is just plain loco. Do you feel lucky?

    2. Terry, you may consider
      Terry, you may consider getting a datalogger that includes carbon dioxide. I haven’t found one I’m in love with yet, but a Hobo or NetAtMo could be on the list.

    3. CO2, carbon dioxide, is
      CO2, carbon dioxide, is normally on the order of 350 ppm outdoors. Indoor levels will tend to be higher.

    4. Terry is most certainly
      Terry is most certainly referring to carbon monoxide (C)) readings. A vent-free heater will generate 10 to 13% Carbon Dioxide (CO2) water vapour and nitrogen dioxide (NO2). There are always going to be traces of methane and CO particularly on a cold start as the heater requires up to 15 minutes to reach equilibrium and it’s optimum combustion state. I’ve been writing about this stuff since the AGA Research Division first published their dubious report in 1996 which was also paid for by the Vent Free Gas Products Alliance.

  2. I’ve been wondering who in
    I’ve been wondering who in their right mind would put one of these things in a really leaky home, let alone the new tight homes builders are producing these days. I did HERS testing on several homes over the last 5 years that had unvented fireplaces and every one of the owners had quit using them because it caused some sort of health issue while in use, from headaches to burning eyes to a uncomfortable feeling in their throat. One lady told me she tried to get the company that sold & installed it to remove it and they refused, so she simply quit using it on her own. I gave her my recommendations too and she said she had figured out most of what I said already through research on the internet. Thanks for confirming the thoughts I have had since I saw the 1st one of these 10 years ago.

    1. Your experience is a common
      Your experience is a common one, Steve.

  3. Perhaps the ten 62.2
    Perhaps the ten 62.2 committee members who voted against prohibiting ventless combustion appliances already have them in their homes and therefore aren’t thinking clearly.

    Occult carbon monoxide poisoning is a recognized medical issue that is often the result of ventless combustion appliances. CO levels are typically low, but still enough to cause health issues, but not high enough to trigger a medical emergency. How much anecdotal evidence is needed to make a statistical argument against burning things inside without venting?

    Anecdotally, I only needed one friend keeling over to know I shouldn’t eat the same mushroom, and I only needed to see one youtube video of a kid trying to use a pogo stick on a treadmill to know when something is a bad idea. A few thousand testimonials from users of ventless combustion appliances should be more than sufficient to reach concensus on prohibiting them.

    As for the manufacturers, let them figure out how to add a flue pipe if they want to stay in business.

    1. Dale, it may be tempting to
      Dale, it may be tempting to think the 10 no votes were from people who don’t think unvented combustion is bad, but that’s not the case. Some are people who do lots of good building science work. They just weren’t ready to vote for a prohibition this early in the discussion. I think the end result of the committee’s deliberations will be something we can endorse.

      1. I agree, Allison. My
        I agree, Allison. My response is more related to 30 years of walking into far too many homes with unvented space heaters and seeing whole families home sick with a “flu” they can’t seem to shake, or at least chronic colds, sinus infections, and asthma in kids. Turning off the heater and opening all the windows for 10 minutes is not what they expect from a stranger that just walked in.

        The 2010 NY State Fire Code still allows unvented space heaters. One only needs to search the CDC website or NIH websites to see all the research and studies about the health issues of unvented combustion appliances.

        It’s a very frustrating part of our industry that we’re still trying to create patched standards to accommodate bad building science and bad products after all these years.

        1. True. And I’m sure many of us
          True. And I’m sure many of us in this industry have had similar experiences. I’ve been in houses with condensation all over the windows and mold growing on the walls because of unvented space heaters.

    1. I didn’t record that, and it
      I didn’t record that, and it’s not really important because this is still early in the discussion.

  4. I’m extremely puzzled by:
    I’m extremely puzzled by:

    “the only reason it didn’t pass is that some members feel the committee hasn’t really seen enough data yet.”

    This is completely contrary to the precautionary principle that needs to apply when catastrophic outcomes (ie deaths and serious injury) are even a suspected possible outcome. The fact of ‘not enough data’ should mean an immediate ban on sales of these appliances in favour of saving lives, rather than allowing continued sales that might well kill or injure people.

    It should not be for more data to prove danger, it should first be up to the sellers to prove sufficient safety before they are allowed to sell even one more such appliance. The precautionary case is clear enough here to say this strongly and immediately.

    Isn’t there a danger of some liability for not acting quickly passing to the committee?

    1. All good points, Paul. The
      All good points, Paul. The committee works on a three year cycle, though, so even if they had approved it at this meeting, the soonest it would go live is in 2019.

    2. By the way, are unvented
      By the way, are unvented combustion appliances banned in Ireland?

  5. We refuse to perform any work
    We refuse to perform any work (other than diagnostics) on a house with an unvented fireplace in it. In a few cases it has cost me jobs (I don’t mind).

    Allison, you reference California and Canada as places that don’t allow them but I thought it was something like 23 states?

    1. Skye, as far as I know,
      Skye, as far as I know, California is the only state that has banned them. Some local areas may have banned them, and there are restrictions on them in some programs, like DOE low income weatherization. I’m planning a followup article on prohibitions and restrictions, so I’ll let you know what I find out.

  6. Massachusetts has banned ANY
    Massachusetts has banned ANY and ALL unvented heaters of ANY kind longer than anyone.

  7. The Commonwealth first
    The Commonwealth first regulated the use of unvented space heaters in 1962, when the legislature enacted M.G.L. c. 148, §§ 5A and 25B, St. 1962, c. 636 and 688, § 1.

    This has been challenged in Court many times and it still is the way to go if you want to protect lives and property, JMO!

    IMO you may just as well bring in a grill and go for it…. doesn’t matter what kind of fuel you’ll be dead anyway, DED, dead!

    1. George, unfortunately
      George, unfortunately unvented products are alive and well in the good old Commonwealth of Massachusetts since 2004. I try to talk consumers out of it on a daily basis and glad it’s not a product of that is sold in my showroom. But competitors all around sell them.

      1. Ooooops, my bad…. When it
        Ooooops, my bad…. When it comes to plumbing and gas, MA can really go out the window, jmo.
        Total review in MA of all Codes starts later this year, so we see what 2018 brings.

  8. I am a member of the
    I am a member of the committee and assure you that there are members of the committee that are interested in protecting the health of the occupants of residences. It is important to recognize that the committee is not just made up of building scientists and that the committee was blocked for years from specifying CO monitors or CO alarms as part of the Standard. The process is not just science based, but also political. While there is no current change to the standard out for public review, hopefully there will be soon (soon to ASHRAE is within the next few years). As I posted in February of 2014:
    ASHRAE Standard 62.2, “Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings” is under continuous revision. John Proctor was a voting member on this standard setting committee at the time it was formed. During that period, the committee was prevented from saying anything about unvented gas heaters also called “vent-free appliances”. These are outlawed in California, but are sold widely elsewhere.

    Mr. Proctor is back on the committee at the same time ASHRAE has allowed the committee to address these appliances. The committee is looking for suggestions as to what they should say about them.
    Please send your suggestions to

  9. Two more items: The
    Two more items: The potentially harmful pollutants are not limited to water vapor and the potential of CO. They also include oxides of Nitrogen.
    Also while the committee only puts out a new standard every 3 years, the Standard is under “continuous maintenance”. Which means that the committee can put our addenda any time as soon as it has the votes and goes through the public review process.

    1. I wonder why it is that you
      I wonder why it is that you don’t also mention the various more serious products of combustion which result from a cold start. It is well documented by AGAR, Warnock Hersey, CSA International and any other accredited test organization that during the first 15 to 30 minutes of from start up most gas appliances, including vent-free emit unacceptable levels of carbon monoxide, soot and traces of raw methane. Air quality in a given home can diminish dramatically depending upon the number of on/off cycles the appliance goes through and the length of each on cycle. This is particularly true of vent-free gas logs in which the flames are impinging on the artificial log, the surface of which is initially cool and therefore not conducive to the cleaner combustion we find as the appliance reaches steady state. These are the very reasons that the committees who wrote the standards allow 15 minutes of normal operation before taking a combustion sample two more minutes before testing in over-fire conditions and two more minutes before testing at reduced supply pressure. I’ve been involved in numerous cases surrounding soot damaged homes and people complaining of health issues regarding their vent-free gas fireplaces. Forget the Rinnai or other ceramic plaque style heaters on the markets. Those low BTU wall mounted supplementary heaters are not the major issue, it is the 30 to 40 MBH simulated fireplaces on both natural gas and propane that are of greatest danger to the unsuspecting consumers.


  10. We have an office in our home
    We have an office in our home (former garage now tightly finished) that is partially heated with a ventless gas heater. I have noticed lately that my memory is not as good sometimes as it is other times. Also headaches. Could these be caused by the heater? My wife is in the office more than me but doesn’t seem to be bothered.

    1. Mel Some people are affected
      Mel Some people are affected more than others on a level they notice. However, just because your wife doesn’t notice the results, her body does. Get rid of the monster even if you have to go to electric heaters.

  11. The biggest concern I have
    The biggest concern I have about flue less is the eventuality of the space filling up with CO 2 then when it is used over again for the combustion air and it is broke down into CO in an enclosed structure! A deadly concern! Any thing over 35 parts per million should be evacuated!

  12. Lance, in this article I was
    Lance, in this article I was reporting on the discussions at the ASHRAE 62.2 committee meeting, not attempting to write a comprehensive article about combustion appliances. I’ve written several articles over the years on the problems with unvented combustion appliances as well as atmospherically-vented (especially natural draft) combustion appliances. I agree with you. Unvented combustion doesn’t belong in buildings. Natural draft doesn’t belong in buildings. If you’re going to use combustion, it should either sealed combustion or outside the building enclosure. (And if it’s outside the building enclosure, it should be a water heater because heating & cooling equipment needs to be inside.)

  13. Paul,
    In the unlikely event that an over-sized vent-free unit was operating continuously in a sealed room and all of the oxygen was consumed the CO2 would be enough to kill you as the human body can’t live with just CO2. More importantly, all vent-free are required to be equipped with ODS (oxygen depletion systems) which are integral to the pilot and designed to shut down the pilot (therefore the unit) if the oxygen levels fall below 18%. Please don’t misinterpret this statement as an endorsement of vent-free appliances I have been fighting against them since about 1994. The ODS pilots are not very accurate and I have tested them under lab conditons down to as low as 14% of oxygen, and at that point the main burner is lifting, floating, ghosting and CO levels begin to go off the charts at thousands of parts per million. Levels that could render you unconscious and dead within a few hours or even minutes of continuous exposure.

    Last I should point out to you that 35 ppm might give you a headache but the CO detectors they sell on the market today can not detect CO levels accurately below 70 ppm. Read the fine print on the instructions that come with them. That is the threshold that UL tests them to. Any device that can accurately read less than 70 ppm would be lab quality and cost thousands.

    Best to simply steer clear of these products and only use vented gas heaters/fireplaces.

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