- BTU
- British Thermal Unit. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit. Heater output is rated in BTUs per hour.
- Carbon fiber heating element
- The flexible heating wire used in most heated apparel. Carbon fiber survives folding and washing better than the older metal-wire elements.
- Convection heat
- Heat delivered by warming air and circulating it. Slower to feel than radiant heat, but it raises the temperature of a whole enclosed room.
- ETL listed
- Tested by Intertek against the same UL safety standard. For a plug-in heater, an ETL or UL mark is the minimum bar worth considering.
- IP rating
- Ingress Protection rating. The first digit covers dust, the second water. IP64 means dust-tight and protected against splashing from any direction.
- mAh
- Milliamp hours, the capacity of a battery pack. Divide capacity by the garment draw to estimate run time, then take roughly 20 percent off for cold weather.
- PTC heater
- Positive Temperature Coefficient ceramic. The element self-limits as it warms, so it cannot run away to an unsafe temperature the way a bare coil can.
- Radiant heat
- Heat delivered as infrared energy that warms objects and people directly rather than warming the air first. It works outdoors where convection heat blows away.
- Tip-over switch
- A safety cutoff that kills power the moment a heater leaves its upright position. Look for it alongside overheat protection on any unattended heater.
- Watt draw
- How much electrical power a heater pulls while running. Watt draw sets both the heat output and the amount you pay per hour to run it.