Depends upon how cold the room the tank in is. If you keep it inside your house and you're one of those who keeps your house at 75, then yeah not much heating needed, if you keep your tank (or sump) in an uninsulated garage then you'll need more heating in the winter.
General rule of thumb I learned (heard about) was 1 watt per gallon per 5 degrees below ambient. So if your 80 gallon tank is in a room that is 70°F normally and you want to keep it at 80°, 80 gallons x 1 watt/gallon x 10°/5° = 150 x 1 x 2 = 300 watts of heating. If the room is normally 65 degrees, then 150 x 1 x 3 = 450 watts. Of course if the tank has a relatively large surface area to volume (e.g. frag tanks) then that number jumps up even more. Now my situation I literally never set the house thermostat to 70°, only when it's really hot (rarely) does it ever get that high in here, so if it were me I'd do what KR said, a 500 watt titanium, or a couple 300 watt titaniums