Many sportsmen and recreationists turn to the so called "vent-free" gas heaters to keep warm in the fall and winter. However, depending on where and how you plan to use your heater, there may be better options available.
Many high output gas heaters need a circulation and an exhaust vent for proper operation. They help to exhaust potentially noxious gases away from the living area, either outside the building or up into the attic. Sure, these vents are vital for safe operation of the heater, but this can lead to energy inefficiencies. The vents also allow heat to escape from your space, which obviously can lead to pretty dismal heating efficiency.
Thanks to their design, vent-free gas heaters supposedly don't require a dedicated exhaust or venting system. There are a number of definitive benefits to this style of heater. The general energy efficiency is significantly better, as you won't be exhausting warmed air into the atmosphere. It also makes this style of heater easier to install and maintain, as there is no ductwork or venting to install.
Many ventless heaters require an electric outlet to ignite. However, you can also find models that can operate without electricity (such as the Mr. Heater Buddy Gas Heater). In spots where a wall outlet isn't handy, this can be life-saver.
Sure, vent-free gas heaters sound great. However, there are a few safety concerns that prevent us from completely recommending them for all uses. While the thought of operating a heater without worrying about venting sounds great, most vent-free heaters still recommend opening a window in the room. Vent-free heaters suddenly seem a little less "vent-free" when you must keep a window ajar when in use.
Truth be told, vent-free heaters will still produce gases that can be dangerous in the right quantities. They are in smaller percentages than your typical propane portable heater, but even smaller amounts of carbon monoxide can be hazardous, as research has shown. To operate them safely, venting will still be necessary to some degree, which defeats the purpose of a vent-free heater quite a bit!
Similar to common oil space heaters, modern gas heaters typically utilize an auto-shutoff sensor that measures oxygen levels in the room. While this eases concerns a bit, I would consider taking things a step further. In addition to following all safety recommendations from the manufacturer, you should also install a carbon monoxide alarm near any running propane heater.
When it comes to warming a well-ventilated area (think drafy cabin, partially-enclosed porch, or tree stand) vent-free heaters can be worth a look. Yet, completely vent-free fuel-based heating is a bit misleading. There are still safety concerns that you should be aware of.