Some of the things to look for in buying a quality ventless gas heater are:

•  At least 25,000 BTU
• Accepts bot Natural and LP Gas
• Should have a separate Thermostatic Heat Control
•  Good units have hand painted logs with lifelike details
•  For safety, make sure the unit you buy has a built In safety sensor
•  Most models have hidden side mounted controls
•  You want a unit that heats at least 1,200 sqft or so

In short, when buying a ventless gas heater, do your homework and buy quality even though it may be more expensive. You will find the attractiveness and long lasting properties to be superior over cheaper models