Don’t Go Too Low

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If you’ve installed (or are about to install) a high efficiency-condensing furnace in your home, you know you are (or will be) saving money on heating. You might be tempted to turn the thermostats down to save even more.  That’s a good idea, but be careful – don’t go too low!  Turning your heat down too much can damage the equipment.

I recently read in Green Building Advisor that turning the heat below 60 degrees (steady) or 65 degrees day/55 degrees night can damage a high-efficiency furnace* and void the warranty. For example, if you read the fine print on a Carrier unit, you’ll find this statement: “This furnace is designed for continuous return-air minimum temperature of 60 or intermittent operation down to 55 degrees, such as when used with a night setback thermostat.  Failure to follow these limits may affect the reliability of heat exchangers, motors, and controls.”

The bottom line is this: condensing furnaces are more efficient than conventional models, but their efficiency comes with the caveat that low operating temperatures can cause condensation of corrosive flue gasses in the primary heat exchanger—and that’s bad.  So even if you’re willing to wear a parka and mittens inside all winter, resist the temptation to turn the heat to 45 degrees!  60 day/55 night is the recommended minimum.

* Note, don’t confuse a furnace and a boiler. This warning applies to a furnace (that heats air) not to a boiler (that heats water).