Digital vs Millivolt Pool Heaters

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.

Millivolt Ignition

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:

  1. you are always using a small amount of fuel, and
  2. millivolt current only travels a few feet down a wire, so it is impractical to use a millivolt heater with any kind of outside control system.
  3. The pilot keeps the interior of the heater warm enough to become an inviting home for small creatures, which can increase maintenance    difficulties. We have had reports of spider webbing clogging burner ports, and rodents chewing through wiring.
  4. Wind buffeting can cause the pilot to be extinguished.
  5. It is a tedious process to accurately set the temperature controls.

Digital Electronic Ignition

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:

  1. you only use fuel when there is a call for heat, and
  2.  if the pilot is extinguished during startup it will automatically relight.
  3. 24V power travels very well down the wires, permitting this design to be used in conjunction with an external control system or certain types of remote control. In addition, 24V power permits the use of digital circuitry, providing far more sophisticated controls.
  4. Temperature control is extremely easy and accurate, and
  5. All connections on the circuit board are plug connectors and are not conducive to the formation of corrosion.  

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.