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What’s the difference between Millivolt Pool Heaters and Electronic Pool Heaters?

Electronic or Digital Pool Heaters have a pilot that lights only when heat is called for. Similar to a modern kitchen gas stove or hot water heater, a small electronic spark ignites the pilot when you turn the heater on. The pilot and the sparker shut itself off after the main burners are lit.

Millivolt Heaters have a Standing Pilot. This means that a pilot burns all the time, like older gas kitchen stoves or hot water heaters. Having a Standing Pilot (Millivolt Heaters) obviously wastes a small amount of gas (about 500 BTUH), but these types requiring no wiring or power from an external source.. It can also attract bugs, rodents and snakes seeking out the warmth it produces.

Electronic heaters are micro-processor controlled, and powered with 24V from an external source, stepped down from either 120V or 240V. Circuit boards, similar to those found in modern computers are used to control and analyze the heater functions. Increase voltage (600mv vs. 24 V) also allows for LED indicators for temperature and troubleshooting, and self-diagnostic functions. Electronic pool heaters also have the advantage of easy integrations with modern pool controller systems, to manage the heater from a remote panel or app.

Millivolt heaters are traditionally controlled by a Millivolt circuit which powers mechanical components in the gas system and the safety circuit. Millivolts are produced by the action of a thermopile, which heats up next to the pilot to create about 600 mv, which powers the millivolt heater. Some millivolt models do not use a flame pilot, but instead light the burners with a “glow plug” type of element, or hot surface ignition, which reduces pilot issues.

How can I tell which type of pool heater I have?

If you have an electronic pool heater, you’ll probably have digital temperature display, or at least a small LCD screen on the panel. Millivolt heaters typically have an on/off switch and a thermostat knob, and digital heaters will have no mechanical switches on the control panel. Electronic heaters will also have a power wire or conduit coming into the side of the heater. A label on the inside of the pool heater door could also help you identify your type of pool heater.

So, Which is Better- Digital or Millivolt Pool Heaters?

Ten to Twenty years ago, I would have said Millivolt heaters are best. Early electronic models had their fair share of irritating problems, coupled with a mental block on working on them, kind of like Old Cars vs. New Cars. But now that understanding of Electronic Heaters has grown, and troubleshooting has become simpler, I would say that for me, I would recommend Electronic (Digital) Pool Heaters.

If you plan to work on this heater yourself, and find the millivolt option easier to work on, like working on cars from the 70’s vs. cars of the 90’s – you may prefer the millivolt pool heater. If you plan to have pool service companies work on it, then I would recommend electronic. In another few years, the knowledge base will switch, and pool techs will be scratching their heads trying to figure out how to work on these old school "confusing" Millivolt heaters. Digital heaters outsell millivolt heaters nearly 3 to 1, even though millivolt heaters are typically a small amount less expensive.

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