HEat pads do not affect the ambient temperature in the cage, so whatever your rooms temperature is is what the ambient temperature should be. (ceiling fans/AC should lower the ambient temperature)

Heating pads can easily get up to 150+ degrees (enough to kill your snake) They will not move if it hits too hot. A thermostat is not optional when using heating pads

Don't waste your money on the thermostats old in pet stores, they are not worth your money.

Here are 2 good thermostats.

The hydrofarm, cheap but effective.These are great if you are on a tight budget but lack accuracy and safety of better thermostats

http://www.amazon.com/Hydrofarm-MTPR.../dp/B000NZZG3S

The herpstat is the best of the best, these are extremely accurate, and have multiple built in safety features, but have a much higher price tag

http://spyderrobotics.com/

Do you have a probed thermometer? Because heating pads do not change the air temperature in the cage you need a probed thermometer to monitor its temp.

This is a good one, sold at Walmart for $12. It measures 2 temperatures (hot side and cool side) as well as humidity.