Every fall the same energy saving tips go around: turn the thermostat down at night, set the water heater to 120°F, upgrade to a high-efficiency furnace, shut the AC off while you’re at work. We wanted to know what each of those is actually worth in dollars for a house in our service area. So instead of quoting national averages, we put the most common energy saving tips through an experiment.
In this article
- The house and the winter we tested the energy saving tips on
- Result 1: The night setback works on a furnace and backfires on a heat pump
- Result 2: Every degree on the thermostat is worth about $25 a winter
- Result 3: The 95% furnace saves $100 a year, which is a 20-year payback
- Result 4: The water heater energy saving tips are real but small
- Result 5: Summer energy saving tips follow the same pattern
- The scoreboard: ten energy saving tips, ranked by real dollars
- What these energy saving tips mean before the cold arrives
- How we tested the energy saving tips
We built a computer model of a typical Northern Virginia townhouse and ran it through last winter, hour by hour, using the real weather recorded at Dulles from November 1, 2025 to March 31, 2026, and then through summer 2026 the same way. Then we changed one thing at a time (the thermostat schedule, the furnace, the water heater setting) and re-ran the whole season to see what changed. Same house, same weather, one variable.
Some of the energy saving tips matched the folklore. One of them was the opposite of it.
The house and the winter we tested the energy saving tips on
The house is an 1,800 sq ft, three-level townhouse from the 1990s with two shared walls, the kind you find by the thousands in Centreville, Ashburn, Manassas, Burke and Alexandria. It has an 80% efficiency gas furnace, a 3-ton central AC, and a 50-gallon gas water heater in the basement. Energy prices are current local numbers: about $1.40 per therm for gas and 17 cents per kWh for electricity.
The winter it went through was a real one. Dulles bottomed out at 2.6°F at 9 AM on January 27, 2026. There were 77 nights at or below freezing and 23 nights at or below 20°F. In our model the furnace’s hardest stretch was January 29 through February 1, when it ran more than eight hours a day, four days straight. Summer 2026 hit 103°F on July 4, with 43 hours at or above 95°F.
Result 1: The night setback works on a furnace and backfires on a heat pump
This is the one that surprised us, and it’s the most repeated of all the energy saving tips.
Dropping the thermostat from 70°F to 62°F between 10 PM and 6 AM saved the gas-furnace house $45 over the winter, about 7%. Adding a weekday daytime setback while the house is empty pushed that to $82. That’s the classic advice and, for a furnace, it holds up as one of the better energy saving tips.
Then we swapped the furnace for a 3-ton heat pump with a standard 10 kW electric backup strip, which is what most heat pumps in Northern Virginia have, and ran the exact same schedule. The setback cost $97 more than just leaving the thermostat at 70°F.
Here’s why. A furnace makes 60,000 BTU an hour no matter what and can pull a cold house back up quickly. A heat pump makes a fraction of that on a cold morning, so when the thermostat jumps from 62°F to 70°F at 6 AM, the house is several degrees below target and the thermostat does what it’s built to do: it turns on the electric backup strips.
Those strips cost roughly three times as much per unit of heat as the heat pump itself. In our model they fired on 144 of 151 mornings and burned about 1,300 kWh over the winter, almost all of it between 6 and 7 AM.
A milder setback (70/66°F) cut the penalty to $40 but still didn’t save anything. We also tested a “smart recovery” thermostat that starts warming up two hours early; it didn’t help, because the strips still engage whenever the house is more than a degree or two below target.
What to do if you have a heat pump: pick a temperature and leave it there, or keep setbacks to 2 or 3 degrees. If your thermostat has a setting that limits backup heat (often called “aux lockout,” “balance point” or “heat pump balance”), turn it on. If you see “AUX” or “EM HEAT” lit up every morning, that’s your electric bill going up, not a malfunction. A heat pump that runs on backup all day in mild weather, though, is a problem worth a heat pump service call.
Result 2: Every degree on the thermostat is worth about $25 a winter
The simplest of the energy saving tips is also the easiest to put a price on.
Holding the furnace house at 68°F instead of 70°F saved $50 for the season. Going to 66°F saved $99. Going up to 72°F cost $51 more. It’s close to linear: figure $25 per degree per winter for a townhouse this size, roughly double that for a large detached house.
Result 3: The 95% furnace saves $100 a year, which is a 20-year payback
Replacing the 80% furnace with a 95% condensing model cut gas use from 454 therms to 383 therms over the winter. That’s $100 a year at today’s prices. A high-efficiency furnace typically costs $1,500 to $2,500 more installed than a standard one (it needs PVC venting and a condensate drain), so the fuel savings alone take 15 to 25 years to pay it back in a townhouse.
That doesn’t mean don’t buy one, and it’s not one of the energy saving tips we’d argue against. It means the reason to replace a furnace is that it’s old, unsafe or unreliable, not the efficiency number on the sticker. If your 80% furnace is 12 years old and working, repairing it is almost always the better financial move. If it’s 20 years old, the calculation changes because you’re buying a new furnace either way.
Result 4: The water heater energy saving tips are real but small
Turning a gas water heater from 140°F down to 120°F saved $21 a year. The number is small because most of what a water heater burns goes into water you actually use, and that doesn’t change with the dial. Only the standby loss, the heat leaking out of the tank while it sits there, goes down. On an electric water heater the same change saves about $40.
An insulation blanket on a gas tank saved another $15 a year. A water heater in an unheated garage instead of a basement cost about $4 more over the winter, less than we expected, because a garage in Northern Virginia doesn’t get all that cold.
The real reason to set your water heater to 120°F isn’t money. At 140°F, tap water can scald a child in seconds, which is why the U.S. Department of Energy recommends 120°F. At 120°F it takes minutes. Set it to 120°F for that reason, and take the $21 as a bonus. (If yours can’t hold 120°F, or the hot water runs out much faster than it used to, that’s usually sediment or a failing element, and it’s worth a water heater inspection.)
Result 5: Summer energy saving tips follow the same pattern
On the AC side, each degree on the thermostat was worth $11 to $12 for the summer. Running at 78°F instead of 74°F saved $46 over June through August. Turning the AC off during weekday work hours saved $21, and letting it drift up to 78°F overnight saved just $4, because Northern Virginia nights in July don’t cool off enough for the AC to stop running anyway.
The biggest single summer number among the energy saving tips wasn’t a thermostat trick. Swapping a 20-year-old SEER 10 unit for a current SEER 14 saved $74 for the summer at the same 74°F setting. Like the furnace, that’s worth doing when the old unit dies, not before.
The scoreboard: ten energy saving tips, ranked by real dollars
Here are all ten energy saving tips we tested, ranked by what they were worth in this house over one season.
| Tip | Worth per season | Verdict |
|---|---|---|
| Replace 80% furnace with 95% furnace | $100 | Only when it’s time to replace anyway |
| Night + workday setback (gas furnace) | $82 | Do it |
| Thermostat 70°F → 68°F | $50 | Do it if you’re comfortable |
| AC 74°F → 78°F all summer | $46 | Do it if you’re comfortable |
| Night setback (gas furnace) | $45 | Do it |
| AC off while at work | $21 | Fine, but small |
| Water heater 140°F → 120°F | $21 | Do it for safety |
| Water heater blanket | $15 | Fine, but small |
| AC up to 78°F overnight | $4 | Not worth the sweat |
| Night setback (heat pump) | −$97 | Don’t |
What these energy saving tips mean before the cold arrives
Two notes before the summary. First, every one of these energy saving tips was measured on one house over one winter, so treat the dollar figures as a ranking rather than a promise. Second, the energy saving tips that need no purchase at all are the ones to try first, since there is nothing to lose if your house behaves differently from ours. Revisit the same energy saving tips each October, because the ranking shifts as gas and electric rates move, and the energy saving tips that won this year may not win next year.
The energy saving tips above are worth doing, but they won’t help a furnace that doesn’t start. Last winter, our model furnace had its first heavy day on December 9 and its hardest four days at the end of January. Furnace repair searches in Virginia nearly triple between September and October, which tells you when people find out theirs isn’t working: on the first cold night, along with everyone else.
If your furnace or heat pump hasn’t run since March, run it for 20 minutes on a cool evening in October and listen. A furnace that short-cycles, a heat pump that goes straight to backup heat, or a burning smell that lasts more than a few minutes is worth a call before the December rush, not during it.
Appliances Pro repairs furnaces, heat pumps, water heaters and air conditioners across Fairfax, Loudoun, Prince William and Arlington counties, Alexandria and Washington DC, 5 AM to 10 PM every day. Call (703) 916-1130 or book online. The service call is free with any completed repair.
How we tested the energy saving tips
The model is a standard hourly heat-balance simulation: the house loses heat through its walls, roof and air leaks in proportion to the indoor-outdoor temperature difference and wind, gains heat from sun, people and appliances, and the heating or cooling equipment cycles on a thermostat with a half-degree deadband, in 10-minute steps.
Weather is the Open-Meteo historical archive for Dulles (38.95°N, 77.45°W), hourly temperature, wind and solar radiation, November 1, 2025 through March 31, 2026 and June 1 through August 31, 2026.
The heat pump’s capacity and efficiency fall with outdoor temperature the way a current 3-ton unit’s do (COP 3.4 at 47°F, 2.2 at 17°F), with 10 kW backup strips that engage when the room is 1.5°F or more below target. The water heater is a 50-gallon tank using the federal test’s 64 gallons of hot water a day, with 55°F incoming water.
Prices: $1.40/therm (Bureau of Labor Statistics, Washington metro) and 17.2¢/kWh (Virginia residential average, September 2026). Your house will differ: a big detached colonial can run double these numbers, a new-construction condo half. The direction of each result is what matters, and the heat-pump setback result in particular holds across every version of the house we tried.