Mainers love to debate home heating practices and especially how to set the thermostat overnight.
It’s a debate that likely goes back to the first time two people heated the same shelter in the cold — reduce the heat at night, or turn it off altogether to better conserve fuel.
Over the centuries, home heating evolved to use a variety of fuels and became increasingly efficient. But that did little to settle the nighttime thermostat argument.
Until now.
Thanks to what we know about thermodynamics and materials science, the answer is at hand. During the winter, the best practice is to turn your furnace down at night, not off.
Any economic savings from turning your furnace off all night is wiped away by how much fuel you will burn reheating your space in the morning.
More importantly, you can create some expensive repair headaches if your home gets too cold.
“In Maine if you turn off your furnace overnight you have to worry about stuff freezing, like your pipes,” said David Dvorak, professor of mechanical engineering technology and director of the New England Combined Heat and Power Technical Assistance Partnership at the University of Maine. “Pipes freezing kind of trumps fuel savings if you have to have a plumber come in on a Sunday.”
Dvorak is quick to say he is not an expert on home heating physics, but he has quizzed furnace technicians and has his own engineering experience to back up what they have told him.
And it does not take an expert in thermodynamics to know it gets really cold during a Maine winter.
Over the last decade, the cost to heat a home in the state during those chilly months has steadily risen. In 2012, home heating oil averaged $3.64 a gallon, according to the Maine Governor’s Energy Office.
In 2012, Firewood averaged $200 a cord, pellets $197 a ton and natural gas $13.67 per 1,000 cubic feet.
Since then, prices have fluctuated with the global economy, political pressures, the pandemic and the war in Ukraine.
According to the latest numbers from the Governor’s Energy Office, home heating oil is at $3.99 a gallon, a cord of firewood averages $350, pellets are $385 a ton and natural gas costs $13.75 per 1,000 cubic feet.
At those prices, it’s no wonder Mainers are looking for ways to save money on heat.
But engineers like Dvorak said it should never come at the expense of your home’s infrastructure.
Especially in older homes that may not be well-insulated or have spaces that are underinsulated, pipes can be very vulnerable to freezing when temperatures drop to 2 degrees Fahrenheit as they did Tuesday night.
Older furnaces with cast iron parts can spring leaks under the stress of constant and drastic cooling and heating.
Even if your pipes don’t freeze, there is no overall savings if you don’t use fuel overnight. That’s due to something called “thermal inertia” and how long it will take to reheat a room.
It’s not just the airspace that has to warm back up, according to thermodynamic and material science engineers.
Walls, furniture and carpets hold and contribute to the warmth of that room. When they get cold, it takes a lot of energy to heat them back up again.
“Solid objects like oak bookshelves or tables will cool down overnight,” Dvorak said. “When you turn your heat back on in the morning, the air will warm up quickly, but the solid stuff is going to take awhile.”
The United States Department of Energy recommends turning your thermostat down at night from 7 to 10 degrees below what you have it set during the day. Doing so can save up to 10 percent of an annual heating bill.
Newer furnace systems have automatic thermostats that turn the temperature down at night and back up in the morning.
“What I recommend is turning your furnace way down but not off,” Dvorak said. “If you want, turn it down to 33 degrees — you just don’t want to run the risk of frozen or leaking pipes.”
Now that the furnace setting question appears to be put to bed, the next debate to resolve among Mainers is, what is the perfect indoor winter time thermostat setting.
Based on the answers from a recent BDN reader poll, this one may take a lot longer to solve.
