I took out three drawers in the cabinet below our TV and put in an electric fireplace a few years ago. It was easy, looks factory installed and plugs into a nearby existing receptacle.
All of the heat is blown out of the front of the fireplace unit so there is no worries about overheating the surrounding cabinet.
The fireplace will warm up the living area and keep it toasty in 40 to 50 degree outside temps. We haven't been in anything under 38 degrees so not sure how it would do in really cold weather.
It has saved having to use the heater to get the chill out in the morning. Plus it provides a little fake fire ambiance while watching TV. Ours even has sound effects you can turn on or off (popping and crackling fire).