NLA = No longer available Set of 5 infrared quartz elements (ie heat bulbs) for EdenPURE third generation heaters or older (see list of compatible units below). Bulbs measure 4.75" not including the insulators on the ends. With insulators, the length is 6.25". Wire leads are 7" long. These are after-market parts. Quality is so amazing that we are offering a lifetime warranty!! Replaces EdenPURE A3823/RP bulb, which is labeled MK2633. These bulbs will not fit the newer Generation 4 (GEN 4) and EP USA 1000 or the smaller 1000 watt EdenPURE heaters. Each bulb is 55 volts and wired as as series of two for 110 volts. 250 watts each bulb for a total of 1500 watts. The longer MK 2634 8" bulb also found inside the heaters rarely goes out but is available separately. To install, remove screws from the bottom and slide the insides out. In some older units the side panels will need to be removed. These 5 bulbs are used in the following infrared units: EdenPURE 1000, EdenPURE 1000 XL, EdenPURE GEN 3 1000, SunTwin 1500, SunTwin 1500 LED, SunTwin 1500 Elite & SunTwin Gen 3 1500 Other compatible products by model number: 1000, 1000 XL, A3705, A4136, A4136/RTL, STW 1500, STC 1500, STW 1500LED, 1500 ELITE, STW GEN 3 & MK 2633 This 5-minute video will show you how to access and replace the 6 heat bulbs in your EdenPURE portable heater.