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A Warm Winter Is Forecast. Will Your Heating Bill Drop?

A winter that runs 1 °F warmer uses about 6% less heating fuel. One hard cold week can give most of that back.

NOAA's winter outlook came out last week, and for most of the northern half of the country the headline is a warmer-than-average winter, pushed by one of the strongest El Niños on record. So yes, if that holds, you will burn less fuel. But less is not zero, and the forecast is a tilt of the odds, not a promise. The useful question is what a warm winter is actually worth to your house, and what to do about the cold weeks that still come.

Your furnace counts degree days, not forecasts

Your heating system does not care about the season's average. It cares about every single day, and how far below about 65 °F (18 °C) that day sits. Utilities call that gap a degree day: the colder the day, the more degree days it adds, and the more heat your house asks for.

Think of a bucket with a hole in it. The colder it is outside, the bigger the hole, and your furnace or heat pump is the tap keeping the water level up. The season's average temperature tells you how big the hole was on a typical day. Degree days tell you how much water ran out in total. Your bill follows the total.

That is why a warm winter saves less than people hope. Across the US, a winter that runs 1 °F warmer from start to finish trims heating fuel by about 6 percent. And the average hides the spikes. A mild December is pleasant, but one hard week in January can add back about as many degree days as that whole mild month saved.

There is one more catch. The outlook compares this winter with the long-term average. Your bill compares it with last winter. Those are different questions, and in some regions they have opposite answers. More on that below.

A few winters back a neighbor skipped his fall furnace checkup after hearing the season would be mild. December was mild. The first real cold snap in January found the furnace with a tired igniter, and he waited two days for a service slot because everyone else's furnace picked the same week.

What to do before the cold shows up

Keep the fall tune-up. A mild forecast is the best possible time to have it done: schedules are open now, and the cold week is still coming. Have the technician check the flue, the filter, the igniter or burner, and on a heat pump the defrost cycle and the backup heat.

Compare bills by degree days, not by calendar month. Some utility bills print the degree days for the billing period next to last year's; if yours does not, your utility's website or a free degree-day calculator will. If the degree days fell and your gas use fell about as much, nothing changed in the house. If use went up while the weather got milder, go looking for a reason.

If you heat with oil or propane, use the forecast to size the fill, not to delay it. The price side is a separate story. The tank side is simple: a week of real cold burns through a half tank fast, and deliveries get slow in exactly those weeks.

If you heat with a heat pump, this is your kind of winter. The milder the outdoor air, the more of the heating it does on its own and the less the electric backup runs. Glance at the thermostat on a cold morning: if the auxiliary heat indicator is on for hours at a time in mild weather, something is set wrong and worth a call.

Wetter where you are? NOAA favors a wet winter across the South and up the East Coast. Keep the outdoor unit clear of leaves and standing water, run the bath fan after showers, and wipe window condensation rather than cranking the heat to chase it.

And call a technician before, not during, the first cold week if the furnace keeps shutting off after a few minutes, you smell gas or exhaust, or the heat pump's outdoor unit stays iced over for hours. Those are not warm-winter problems. They are the problems a warm winter lets you ignore until the week it cannot.

The call I get most in a mild winter is "my bill went up and the furnace must be failing." Half the time I pull up the degree days for that billing period and the month was simply colder than the same month a year earlier, often by more than the bill rose. The furnace was fine. The weather was not.

Go deeper: degree days, balance points and El Niño

A heating degree day is the gap between a base temperature and the day's mean temperature, counted only when the mean is below the base: HDD = max(0, 65 − T_mean). EIA and most US utilities use 65 °F; Korea uses 18 °C. The base is really a balance point: the outdoor temperature at which people, appliances and sun cover the house's losses and the system idles. Above it, seasonal heating energy scales almost linearly with degree days, roughly (UA ÷ efficiency) × HDD × 24, plus a hot-water and cooking baseload that ignores the weather.

EIA's October outlook (October to March) puts the US at 3,155 population-weighted HDD, unchanged from last winter: Northeast 4,331 (−12%), Midwest 4,802 (−2%), South 2,021 (+1%), West 2,781 (+25%): last winter in the West ran far milder than the one EIA now expects. Over 182 days the US average is about 17 HDD per day, so 1 °F all winter is about 5.8% of heating fuel; in the Northeast, near 24 per day, 4.2%; in the South, near 11, 9.0%.

Worked example: a Northeast gas house burned 60 Mcf last winter, 50 for space heat and 10 for hot water and cooking. With 12% fewer degree days the heating share drops 6.0 Mcf, about 6.2 million BTU or 1,800 kWh of gas (170 m3): about $97 at EIA's Northeast forecast price of $16.12/Mcf, before the separate 9% price cut EIA expects. The same house in the West, at +25%, burns 12.5 Mcf more, about $189 at $15.10/Mcf. EIA's 10% warmer and colder cases move it ±5 Mcf, about ±$81. On spikes: a month 2 °F warm saves 31 × 2 = 62 HDD; one week 10 °F below normal adds 7 × 10 = 70.

Why El Niño: the National Weather Service expects a very strong event to shift the jet stream south and east, favoring a warm north and a wet South and East Coast. The probabilities are a tilt, about 45 to 55 percent for a warm winter around La Crosse, Wisconsin, where 5 of 9 strong El Niño winters since 1949-50 landed in the warmest third, and January 1966 still averaged 3 °F at nearby Rochester.

EIA forecast heating degree days for this winter compared with last winter, by region.

Sources

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