There is some confusion as to how many Amps the heated Pitot tubes draw, what circuit breaker to use, and what wire size to use.
Make of Pitot 
Model AmpsCircuit Breader to useWire size
Gretz Aero GA-1000 .1 - 7 Amps 10 Amp 14 ga.
Aero Instruments PH502-12CR 8 Amps 10 Amp 14 ga.
Aero Instruments AN5812 8 Amps 10 Amp 14 ga.
Aero Instruments AN5814 12 Amps 20 Amp 12 ga.
note: The Aero Instruments AN5814 draws a tremendous amount of current at turn-on, but it drops to about 12 Amps after it has heated up (about 45 -60 seconds). We have not been able to accurately measure this turn-on current, however, we have seen 35 Amps for a fraction of a second right at turn-on. It does rather quickly drop to the manageable 12 Amps in less than a minute. It is recommnded to use a 20 Amp circuit breaker. Circuit breakers are slow to react to high current loads. Or, one can use a slow-blow fuse.
The Gretz Aero GA-1000 heated Pitot tube is unique in that it only has the heater on when heat is needed to keep the Pitot safe. When power is supplied to the electronic contol module and heat is not called for by low temperatures, the module is all that draws current. In this stand-by mode the Pitot system will only draw .1 Amp. When the Pitot tube is calling for heat and the electronic control module switches on power to the heater it will draw 7 Amps. It will continue to switch on and off as conditions change to keep the Pitot tube at a safe temperature. By cycling on and off, the Pitot system does not require as much overall draw of current to the aircraft electrical system. This means that the GA-1000 is a wonderful match for small electrical systems in light aircraft.
If you have a Pitot tube from some other manufacturer, you will have to contact that company to find the Amperage of their Pitot tube. The above information should give you a general guideline to select wire size and circuit breaker.
The wire sizes shown in the above chart is for a heater wire in a bundle of other wires and not a single wire in free space.
