Space Heaters

By: Russ Zeckner, P.E., CFEI
A space heater is a device designed to warm a small area.  These devices are typically portable, but the category does include gas- and wood-fueled models that are permanently installed; however, these are not the focus of this article. The National Fire Protection Association (NFPA) reported that “in 2010, heating equipment was involved in an estimated 57,100 reported U.S. home structure fires, with associated losses of 490 civilian deaths, 1,530 civilian injuries, and $1.1 billion in direct property damage.  These fires accounted for 15% of all reported home fires.”[1]  While these statistics are sobering, it must be noted that heating equipment fires have moved down from their status as the most common cause of residential fires in 1980 to third place in 2011, and related deaths declined from a high of 730 in 2005 to 400 in 2011. Although the Consumer Products Safety Commission (CPSC) reports that dozens of different brands and models of space heaters have been recalled because of their potential to cause fires and injury, most such incidents can be traced to mistakes made by their owners.[2]  The NFPA states that 24% of all space heater fires were caused when the heater was placed too near combustible materials.  More disturbing, this easily preventable fire cause has resulted in 58% of all space heater-related fire fatalities.  Although they cannot be ignored, fires caused by defective appliances were not significant enough to warrant a category in NFPA’s statistics. Because of the efforts made by organizations such as Underwriters Laboratories (UL), NFPA, CPSC, and many others both governmental and private, manufacturers of space heaters now produce products with a variety of safety features and designs that are intended to minimize potential fires.  Automatic high-temperature and tip-over shutoffs are required on all UL-approved space heaters.  Many electric heater types such as ceramic and oil-filled models do not have hot surfaces and therefore are less probable to ignite nearby combustible materials than those with extremely hot and exposed resistive heating elements or lamps. All electrically-powered space heaters have another hazard that is related to their power cords.  A typical electric space heater requires about 1,500 watts of energy, and therefore, approximately 12.5 amperes of current must flow through its power cord.  Assuming the space heater is UL approved, the power cord will be properly sized to accommodate this current flow.  If anything happens to that cord that reduces the internal wiring’s cross section, the electricity will be forced to travel through a smaller area, and a phenomenon known as resistance heating can occur.[3]  Resistance heating can produce temperatures sufficient to melt away the cord’s insulation and ignite adjacent materials such as rugs, causing a fire.  Kinking, twisting, crushing, and partially cutting are just a few of the ways to inadvertently compromise a space heater’s power cord. An electric space heater’s power cord is not intended to be used with an extension cord.  Not only is the wiring within a typical household extension cord too small for the power that the heater requires, its additional length also adds to the resistance and therefore the heat that is produced within the cords. This excess heat can lead to a fire. Kerosene-fueled heaters pose other challenges.  Mistakes made by the user during filling and ignition of the appliance can result in a fire, but more often the problems with these heaters are more insidious.  Fueling with gasoline had contributed to numerous fires in these heaters.  Such heaters also have various safety devices that minimize the fire hazard if tipped or if the appliance overheats, but they also can ignite combustible material placed too near. Because a kerosene heater, or any other combustion appliance, produces its warmth by burning a fuel, byproducts are produced.  If the combustion process is perfect, the only byproducts are carbon dioxide and water vapor.  When this ideal state is not achieved, elemental carbon (soot) and carbon monoxide are produced as additional byproducts.  Manufacturers of kerosene heaters incorporate a platinum catalyst that will compensate for slightly less than ideal combustion.  Unfortunately, the catalyst cannot overcome large deviations from the ideal combustion, and episodes of soot and carbon monoxide production are not uncommon.  Most commonly, these damaging and potentially lethal events are the result of poor wick maintenance or adjustment, and the use of improper or contaminated fuels. Millions of space heaters are used for countless hours each year to safely provide warmth and comfort.  Problems, some tragic, will result when the appliance is improperly used or maintained.
[3] Resistive heating is analogous to placing one’s thumb over the end of a hose while the water flows out slowly.  The reduction in area produced by the thumb causes the water to spew out faster in order to allow the same quantity of flow to be maintained through the constricted hose end.