Approved indoor burning devices

Certain brands and models of burning devices are exempt from the regulation that bans indoor burning in the seven-county metro Denver area on air quality Action Days, and may be exempt from other municipal or county restrictions on burning devices. Check with your local jurisdiction for more information. These devices have been approved by Colorado or certified by the U.S. Environmental Protection Agency (EPA) and are designed to emit low levels of pollution.  
If indoor burning is your only source of heat, an uncertified or unapproved device may be exempt and allowed for use. 
Uncertified devices
It’s illegal to install uncertified burning devices in the seven-county metro Denver area, or to sell new or used uncertified burning devices in this region. An EPA "qualified" fireplace is not a certified device. According to regulation, if the device does not meet certification requirements it may not be advertised for sale, offered for sale, sold or installed in Colorado.
The law about indoor burning restrictions