I have one exactly like the Williams in your picture. It is supplementary heat to the room I spend most of my time in for winter.  It puts out good heat . It operates on natural gas just fine even if the power goes off but it does have the optional fan too. My only complaint is that it is hard to start in the fall after I've had it shut down with the pilot light out all summer. Replaced the thermocouple a few times and another time there was a blockage in the line to the pilot. Its probably 25 years old so maybe time to replace.