Temps and infrared wattage help, 20 gallon tank

[ridingtheclouds]

I need to know what wattage I should have to heat my whole tank to the temps they need to be. I plan on buying 2 different lamps/bulbs for the cool and hot sides of the tank. My house is 68°F during the day and around 64°F at night. That is why im thinking I will need a lamp for the cool side of the tank. My question is, what wattage is recommend for both temps of the tank? I will be using infrared bulbs in a 20 gallon tank, Thank you!