Our residential line of pool and spa heaters are generally available in 2 different ignition styles: millivolt, or electronic. The differences between them are significant, and should be taken into account when designing or replacing your heating system.
This design has a constant pilot, sitting just below a small generator. This generator uses the heat of the pilot flame to generate small amounts of power (milli-voltage, or thousands of a volt). This trickle of power is then used to operate the rest of the system. The pilot operates at about 500 BTUH.
The advantage of using millivolt ignition is that no electrical power needs to be supplied to the heater. The heater can therefore be located in areas where no electrical service is readily at hand, or where it would be prohibitively expensive to provide electric service.
The disadvantages of using millivolt ignition are that:
This design only generates a pilot when there is a call for heat. Keeping the sensors active requires electrical power, so power must be wired to the unit. The internal transformer will accept either 120V or 240V power, and transforms it to 24V for use within the heater.
The advantages of using electronic ignition are that:
The disadvantage of using electronic ignition is that there is always a call for small amounts of power (about 1 amp).
In addition, millivolt ignition is no longer allowed with natural gas in certain areas (such as California) because of concerns about fuel usage when the unit is not firing. Please consult your local authorities to see if they have specific requirements about pool heater ignition systems.