Radiant Heat Panel for BRB

[tmconlwy]

So I'm planning on using a RHP for my Brazilian Rainbow Boa but I'm not sure if I should go with a 40 watt or an 80 watt as this will be my first time using a RHP. As I'm sure y'all know, BRB's do not require high heat so I don't want to get the wrong one and make his enclosure too hot. I'm building a 24"x60"x36" (2'x5'x3') PVC enclosure and my house typically stays at 72 degrees (might fluctuate a bit but never below 70) Thanks everyone!