I haven't taken the time to read the other replies, but that having been said, here's my experience with them:
In my former house, we had two of them installed. They are the fireplace type, with mantels, that look like a real fireplace but are propane. I absolutely LOVED them!! They hooked up to our existing propane tank, but we had to have new lines installed leading from the fireplaces to the existing tank of course. I lived in Massachusetts at the time, and the state regulations required a safety inspection and Carbon Monoxide alarms to be installed in each room where the fireplaces were. No big deal. They are extremely efficient. One of them, the more expensive one, had a remote control, and I absolutely loved setting the table for dinner and clicking on the fireplace from the table. The larger one would blow you out as far as heat goes, we always had to keep it on low. The other one was in a larger space and was not overpowering.
I would highly recommend them. I miss them a lot. An added bonus was that we had a nice heat and light source during power outages. Hope that helps!