Is a vented or vent-less natural gas burning log set the right way to re-purpose my old fireplace? This is not that easy to answer as it really depends on a lot of factors; the first one being what you expect the log set to do for you.
Typical gas fired log sets are primarily intended for aesthetics and are not really made for heating your home. Their design is such that most of the heat given off is typically lost up the chimney in a vented appliance, and much of it is also lost through the open door or window in a vent-less application.
Recently this has been a hotly debated topic, and if you were to go ask a professional who works with fireplaces on a regular basis you might find that many of them would not recommend a vent-less fireplace log set of any kind. It is very funny to me that the operating instructions for many of the available vent-less gas appliances instruct you to open a window or door so that sufficient make up air can come into the home. Call me a rebel but does this not defeat the purpose of heating with a vent-less appliance?
If you have your mind made up that vent-less is the way to go, there are specific guidelines that should be used when determining the proper size of your gas log set. The National Fire Protection Association has documented a “National Fuel Gas Code” which details exactly how to size a gas appliance for non vented operation. The formula basically takes into consideration the BTU output of your gas log appliance and stipulates that you need a certain quantity of make up air in cubic feet for each 1000 BTU’s per hour your appliance puts out. The exact calculation for your situation can be obtained from any reputable fire log set dealer.
Direct vent log sets versus vent less? In my opinion vent-less gas log sets are not the wisest option, especially if you are trying to save money on your heating bills. It may sound like a great idea at the time, but if you already have a working chimney then it makes sense to remove the combustion gases including carbon monoxide from your living space.
Think about it would you fire up your outdoor gas grill in the house? Would you burn the propane garage heater inside your home? probably not. Whether you use natural gas or propane the most important consideration is safety. This consideration is two pronged, first health safety for occupants, and second is fire safety. You certainly do not want to have breathing or headache issues due to your non vented fire logs, and I can not imagine anything worse for a homeowner than having a house fire due to a poorly installed fire log set.
I know some of you are thinking hey what about my gas oven and top burners? Well there are a number of significant differences, and while it is true that natural gas stoves give off similar emissions to that of a natural gas fired log set, however they are not usually large enough to put out the same level of BTU’s as a fireplace log set.
Plus the flame is optimized to create a blue flame for optimal combustion, and not a yellow flame generated simply for aesthetics. This is done by altering the balance of combustion air to gas ratio which in turn changes how completely the combustion process works. Gas fired stoves are not meant to be operated for extended periods of time, and are not meant for heating your home. Lastly ranges are typically vented via a range hood that removes the combustion gases as you are cooking.
To my way of thinking there are far too many downsides to using a vent-less gas fired burner of any kind. With the health and safety issues covered, you have to consider the final of the big three as the moisture given off by the combustion process. This moisture can build up on surfaces in the home creating a breeding ground for mold, which is always present, but does not always have the right conditions to propagate and thrive. Excess moisture from a non vented gas log set can be the trigger for creating such an environment that mold can thrive.
Also consider that for every cubic foot of venting going up the chimney there is equal amount of make up air coming from outside the house. This air all needs to be conditioned somehow. It is usually the house furnace that has to reheat the incoming air so that the rest of your house does not feel cold. So yes you will feel warmth around the gas fired log set, but the rest of your home could be much colder. In most applications that I have seen typical gas log sets by themselves cannot create enough heat to offset the losses which is why some people are inclined to consider the use of vent-less fire log sets.
There is a safer and better way to go about using both an existing fireplace and a natural gas fired log set. This calls for having a fireplace insert installed which has an external vent connection that brings make up air into the burner, and also vents the exhaust out of the appliance in a safe fashion. These usually have a fan unit that can bring more heated air off the unit than you can get using just normal convection. Fireplace inserts are much more efficient at keeping the heat inside your home since they do not let warm house air draft up and out of the chimney which can occur even when not in use like a regular fireplace can.
Finally carbon monoxide is a serious danger in any combustion process, and any gas fired appliance that does not have proper ventilation can cause illness and even death. Carbon monoxide poisoning symptoms can include nausea, shortness of breath, dizziness, headache, loss of consciousness, being disoriented, fatigue, and vomiting.
If something does not seem right quickly get yourself and your family to safety and vent copious fresh air into the area that is suspected of having built up carbon monoxide. Shut off gas supply if it can be done safely. Call the fire department ASAP!!
So in summary, I am personally opposed to using any vent less gas fired appliance inside a home. There are better and more efficient ways to heat your home, and these log sets are more of an aesthetic device.
This article is based on many years of working on various combustion processes, including boilers on steam turbine driven ships, natural gas boilers at steel mills, and various home furnaces, water heaters, stoves, and gas log sets.
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