One number, one schedule, and nobody touches the thermostat

The case

Since Halloween, the thermostat in our hallway has been adjusted more often than the baby. I set it to 66. My wife, Dana, sets it to 72. Neither of us has ever been caught doing it. The furnace kicks on and off like it's trying to remember why it walked into the room.

So we took it to Grandma. Fifty years of running a house, four kids, eleven grandkids, one husband who once tried to fix a dishwasher with a butter knife. She loves both of us. She doesn't do "agree to disagree." She does Sunday dinner and she does verdicts.

Exhibit A

I'll argue my side, because it's a decent side.

I run warm. I always have. At 72 I lie awake at two in the morning with one leg out from under the covers like a dog on a porch. A cooler house is cheaper to heat, and the December bill came in higher than November's, which I mentioned at dinner. Twice.

And there's the layering principle. Somebody who's cold can put on a sweater. Somebody who's hot can only take off so much before it's no longer appropriate at the dinner table. The math favors the cooler house. I've said this many times, usually while wearing shorts in January, which I'm told doesn't help my case.

Exhibit B

Dana's turn, and she's fair even when she's winning.

She works from the kitchen table three days a week. At 66 her fingers go stiff on the keyboard by ten in the morning. "I shouldn't need a coat to answer email in my own house," she said, and Grandma nodded so hard her reading glasses slid.

Then Dana brought the receipts. The bill isn't up because of her 72. It's up because somebody keeps changing the setting all day, and because one cold morning somebody cranked it to 80 "to warm it up faster" for the kids, then forgot, and the house hit 79 by lunch.

That somebody was me. Exhibit B rests.

Grandma's ruling

Grandma folded her napkin, which is how you know.

"A thermostat is not a steering wheel. You don't keep your hands on it."

She turned to me. "Setting it to 80 doesn't heat the house faster, honey. The furnace makes heat at one speed. You just told it where to stop, and you told it wrong. Yelling louder doesn't make a furnace hurry. That's a furnace, not a teenager."

Then to both of us.

"Your grandfather and I had this exact fight from 1971 to 1983. I settled it with a cardigan and a plastic cover from the hardware store. He wore that cardigan to his retirement party. He told everyone it was his idea."

The ruling:

• Days are 68. Dana gets a heated throw for her chair. I wear a long-sleeved shirt, like a grown man in winter.
• Nights drop to 62. I sleep like a rock. Dana gets an electric blanket on her side of the bed and is, by her own report, finally warm.
• The schedule goes in tonight, and after that nobody touches it. Whoever changes it off schedule unloads the dishwasher for a week. Grandma looked at me when she said "whoever."

"You're both right about being cold and being hot," she said. "You're both wrong about fixing it with the hallway. Heat the person. Leave the house alone."

Then she served pie, which in her court means the case is closed.

The practical part

You can run this in your own house tonight. It takes about fifteen minutes and one honest conversation.

1. Agree on the numbers before anyone touches a button. The U.S. Department of Energy suggests 68°F in winter while you're awake, and lower while you're asleep or out. In summer, it suggests 78°F when you're home. Use those as a starting point and settle within a degree or two of them. Talk it out at the table, not at the thermostat.

2. Use a setback, and program it once. The DOE says turning the thermostat back 7 to 10 degrees for eight hours a day can save up to 10 percent a year on heating and cooling. Overnight is the easy eight hours. The old idea that reheating a cold house wastes more than you saved is a myth. A lower setting means less heat leaking out.

3. Don't crank it. On most home systems, setting 80 won't reach 70 any faster than setting 70. You'll just overshoot and pay for it.

4. Heat pump? Go easy. A big setback on a heat pump can trigger the backup electric heat strips, which are expensive to run. Use smaller setbacks or a thermostat built for heat pumps, and ask your HVAC technician what suits your system.

5. Heat the person, not the house. The cold one gets wool socks, a throw, an electric blanket. The hot one gets lighter bedding and a fan. That's cheaper than moving the whole house three degrees.

6. Space heaters and electric blankets need real rules. No joke on this one. Plug a space heater straight into a wall outlet, never an extension cord or power strip. Keep it at least 3 feet from anything that can burn, including bedding, curtains and the dog's bed. Buy one with automatic tip-over and overheat shutoff. Turn it off when you leave the room or go to sleep. Use electric blankets exactly as the manufacturer says, and replace any with frayed cords or hot spots.

7. Do the boring maintenance. Check your furnace filter monthly and replace it when it's dirty or when the filter's label says to. Keep furniture and rugs off the vents. If you heat with gas, oil or wood, keep working carbon monoxide detectors near the bedrooms and test them.

8. Make it a house rule, not a mood. One schedule, one penalty, revisited once a season instead of once an hour. If you've ever wondered what separates a rule from a grudge, this piece on the difference between a household standard and a bad mood is worth your time. If the thermostat is really a stand-in for a bigger fight over the bills, start with when you and your wife don't agree about money.

It's been three weeks. The furnace runs like a furnace again. Dana types in short sleeves under her throw. I've unloaded the dishwasher twice, both times for touching the thermostat.

For Grandma's birthday I bought her a cardigan. She thanked me, then told me she has six, and that every one of them won an argument.