Short answerThe biggest heating bill savings in a Michigan winter come from an 8 to 10 degree overnight setback, sealing duct leaks in the basement, air sealing and insulating the attic, keeping indoor humidity around 35 percent so a lower thermostat setting feels warm, and a clean filter. Replacing an 80% furnace with a 96% unit cuts gas use about 15 percent and is the largest single step.
Where the gas actually goes
A typical house in the Ypsilanti area burns somewhere between 600 and 1,200 therms of natural gas a year, and most of that goes through the furnace between November and March. The bill is driven by three things: how much heat the house loses, how efficiently the furnace replaces it, and how warm you ask the thermostat to keep it. Every item below attacks one of those three. They are ranked roughly by how much they save per dollar spent, based on what we see across homes from the prewar cores of Ypsilanti and Ann Arbor to the 2000s subdivisions in Canton and Saline.
Setbacks: the free one
A programmable or smart thermostat set 8 to 10 degrees lower for the 8 hours you sleep and the hours the house is empty saves a real percentage of the gas bill, commonly cited at 5 to 10 percent, with no cost beyond the thermostat. The myth that the furnace "works harder to catch up" and erases the savings is wrong for a gas furnace; the house loses less heat when it is cooler inside, period.
Two refinements. First, do not set back so far that pipes on exterior walls get cold; 60 to 62 overnight is a reasonable floor in a 1920s bungalow with no wall insulation. Second, if you have a heat pump, use smaller setbacks or the thermostat's built-in recovery logic so the electric backup strips do not kick in at 6 a.m.
Airflow: the filter and the ducts
A clogged filter makes the blower work harder and the heat exchanger run hotter, and on a high-limit trip the burner shuts off while the blower keeps running, so you are paying to move cold air. Change it on the schedule in how often to change your furnace filter.
Ductwork is the bigger story. In the 1950s-70s ranches that fill Westland, Garden City, Wayne and Ypsilanti Township, the supply trunk runs through the basement with branch takeoffs that were never sealed, and the return is often a panned joist bay that leaks at every seam. A quarter of the heated air going into a basement that does not need it is not unusual. Sealing accessible joints with mastic, not cloth duct tape, is cheap and effective, and it is the first thing we suggest when someone asks about a high bill in an older house. Ductwork leaks in older Michigan homes covers what to look for, and our ductwork repair service handles the parts that need sheet metal work.
Open every supply register and keep furniture off the returns. Closing registers to "save heat" in unused rooms raises static pressure, cuts total airflow and often costs more than it saves.
The attic and the envelope
The furnace replaces the heat the house loses, so a house that loses less needs less. In Southeast Michigan's housing stock, the attic is usually the worst offender.
- A 1960s ranch in Livonia with the original 3 to 4 inches of blown insulation should have 14 to 16 inches (R-49). Adding it is one of the highest-return investments in the house.
- Air sealing matters as much as insulation: the attic hatch, the plumbing stack, recessed lights, and the top plates of interior walls all leak warm air into the attic. Seal before you insulate.
- Rim joists in the basement, where the floor framing sits on the foundation, are often bare. Foam board or spray foam there is an afternoon project with a noticeable effect.
- Old double-hung windows in a prewar Ypsilanti two-story leak at the sash. Storm windows, weatherstripping and a plastic film kit help more than most people expect; replacement windows cost a great deal and save relatively little gas.
DTE's home energy assessment program and Michigan's HOMES rebates can subsidize some of this work; Michigan HVAC rebates and tax credits has the details.
Humidity: the comfort multiplier
Dry air feels colder. At 20 percent relative humidity, which is where an unhumidified house lands on a January day, 70 degrees feels like 66, so people push the thermostat to 73. At 35 to 40 percent, 68 feels comfortable. A whole-home humidifier that lets you run the thermostat two or three degrees lower saves gas every hour the furnace runs, on top of the comfort and static-shock benefits. Keep it in the 30 to 45 percent range and lower it in a cold snap so windows do not frost. Whole-home humidifier benefits in a Michigan winter explains the mechanics, and humidifier maintenance covers keeping one working.
The furnace itself
Maintenance. A furnace with a dirty burner, a weak flame sensor or a blower wheel caked in dust runs less efficiently and cycles more. A fall tune-up with combustion readings keeps it at its rated efficiency. The furnace tune-up checklist shows what that includes.
Efficiency. An 80% furnace sends 20 cents of every gas dollar up the chimney. A 96% condensing furnace sends 4 cents. On a 900-therm house, that difference is roughly 150 therms a year. The upgrade costs real money, covered in new furnace cost in Michigan, and it rarely makes sense to replace a working 10-year-old furnace for efficiency alone, but when the furnace is due anyway, the 96% choice pays back through our long heating season and the DTE rebate and federal credit it unlocks.
Staging. A two-stage furnace running on low most of the time wastes less heat in the exchanger warm-up and shutdown on each cycle and keeps rooms more even, which means less temptation to raise the setpoint.
Blower. An ECM blower uses a fraction of the electricity of an old PSC motor. In a house that runs the fan continuously, that is a visible line on the DTE electric bill, not the gas bill, but it is money.
The things that do not work
- Space heaters to "take the load off the furnace." Electric resistance heat costs roughly two to three times as much per BTU as DTE natural gas through a 96% furnace. A space heater is fine for one cold room for an hour; it is not a savings strategy.
- Closing vents and doors to unused rooms. Covered above; it usually backfires.
- Fireplaces. An open wood-burning fireplace pulls more heated air up the chimney than it puts into the room. Close the damper when it is not in use; a leaky damper on a prewar Ann Arbor house is a hole in the envelope all winter.
- Turning the furnace off and on manually. The thermostat does this better.
- Furnace additives, magnets and gadgets. None of them do anything.
A reasonable order of operations. Set the schedule on the thermostat tonight. Change the filter this week. Seal the basement duct joints and the rim joist this month. Get the attic assessed before the next heating season. Keep the humidifier at 35 percent. Have the furnace tuned every fall. When the furnace is due, buy the 96% two-stage with the ECM blower. Done in that order, a house in Pittsfield or Belleville can realistically take 20 to 30 percent off a winter gas bill, and the first three steps cost almost nothing.