The Chimney Sweep Online Fireplace, Woodstove, Gas Stove and Barbecue Shop
The following is an exerpt from a November, 1998 article in Consumer Reports Magazine outlining the results of their independent testing of vent free gas fireplaces.
"....our tests confirm that these heaters contribute significantly to indoor air pollution. If you're planning to buy a gas fireplace, a vented model should be your first choice. That's especially wise if any household member has asthma or another respiratory ailment that may be exacerbated by particulate matter, or if your home is very airtight--and so will disperse the fireplace's emissions less readily. A vented gas fireplace needn't cost more to buy and install than an unvented model, since some units require only a fairly small vent pipe that runs horizontally to any outside wall."
The same warning was repeated on Consumer Reports Magazine's website in January, 2008.
Read about a 2016 ASHRAE standard that could eliminate the entire vent-free product category in the US
Have a vent-free experience you'd like to report? Here's a link to the Consumer Product Safety Commission website.