Hmmm... good question. Sorry I took so long to reply. It's been a while since I logged on here. I think it's a 10 watt. I bought it at Walmart. It's a Tetra brand Whisper heater-made for 2-5 gallon tanks. Not an ideal heater, I wish it'd make the water warmer. It keeps Patriot's tank at about 72 degrees.