If you have any kind of vent free gas system, please make sure it is safe. I just had a man over to talk about installing a system like that. We have some pretty cast iron older units that we had disconnected on the advice of our home inspector. The guy today verified that they would not be safe (no oxygen regulator or something like that) and told me a few scary stories of clueless people still using them, even one local hotel! We have high ceilings around here so people get away with it for the most part but you don’t want to risk that!
We had a gas log set (and attached through the wall a propane tank) inserted into our previous wood-burning fireplace. The pilot light stays on all the time and the remote ignites it . Very easy. We leave the pilot light on through the summer because in our area spiders are attracted to the additive in propane and will nest in the line if it’s not running.( You can pay for the small amount of propane the pilot light uses all summer or you can pay a service fee to have the spiders flushed out of the line in the fall !)
Agree with previous posters that we use it for slight amount of warmth and “ambience” - not as a primary heat source of any type here in the cold mid-Atlantic region.
My fireplace insert is manufactured by Travis Industries, Kirkland WA. Model FPX 44 with the Artisan face style in copper. It is vented at about shoulder height outside the house (about 12" square). We can adequately heat our 600 s.f. great room without additional heat from our furnace, however we live in the S.F. Bay Area where temps rarely drop below 40 degrees in the Winter. Flipping a switch is so convenient, and adjusting the fan output takes just seconds.
The only issue for us is a small amount of heat can be detected radiating from the unit all the time. During the warmer months I wish this wasn’t the case.
@jshain, thank you for supporting my local economy. 
I just lit our fp… flipped the switch on the wall. The brand is Majestic. During the apocalypse of December 2006, the 2 fp kept our house at 60 degrees fro 7 days when we had no power.
I have a DIRECT VENT gas fireplace made by HeatandGlo. The combustion air vents outside and is pulled in from outside; the inside cooler air flows in the bottom of the unit,heats as it goes by the sealed firebox then exits the top vents. The unit looks like a fireplace with glass in front and is rated as a furnace. It puts out a lot of heat and is very useful when there is no electricity to light our real furnace… plus we love it and have used it for 17 years. We bought the lower-budget one with a pilot light, which we light in the winter and extinguish in the spring.