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.

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.

Regards.

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.

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?

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.

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.

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.