Question: I'm adding a family room (around 420 sq ft) and want to look at a gas heater as my primary source of heat. From reading your web pages- it seems like vent-free heaters/fireplaces are not intended for primary or unattended heating. Am I thinking correctly that I should pursue a vented heating system since it will be running frequently and unattended (i.e. overnight)?I've also heard that vent-free heaters can cause moisture buildup in the room or even pose a carbon monoxide threat. Your thoughts? Answer: Go for the vented - direct vents are great. Vent-Free are not for overnight and unattended use. Even the vent-free manufacturers agree on this!