If your electric bill jumped and it’s summer or winter in North Carolina, the heating and cooling system is the first suspect: in winter the most common cause by a wide margin is auxiliary (strip) heat running for hours; in summer it’s a system that’s losing refrigerant, running with dirty coils or a clogged filter, or fighting duct leaks in a hot attic or crawlspace. Compare kilowatt-hours (not dollars) to the same month last year, then work down the list below from most likely and cheapest to fix.
First, confirm it’s usage
Pull the kWh from this bill and the same month last year. If dollars rose but kWh didn’t, it’s a rate change. If kWh rose, look at what changed: weather (compare degree days if your utility shows them), occupancy, a new appliance, an EV, a pool pump. If none of that explains it, HVAC is next. Many utilities show hourly usage online; flat blocks of high draw overnight in winter are strip heat, and a rising baseline through summer is a system losing capacity.
Winter causes
Auxiliary heat. Resistance strips cost two to three times as much per hour as the heat pump. Thermostat setbacks that are too large, no aux lockout, a thermostat not configured for a heat pump, emergency heat left on, or a heat pump that isn’t heating well all put the strips to work for hours. This is the number-one winter bill problem in this climate. Aux heat stuck on.
Heat pump underperforming. Low refrigerant, dirty coils or defrost trouble drop output; aux fills in expensively.
Duct leaks. Warm air lost to a crawlspace is heat you pay to make twice.
Summer causes
Refrigerant loss. A system low on charge runs longer and longer for less cooling. Bills climb over weeks. Needs a leak repair, not a top-up.
Dirty filter, coil or outdoor unit. Every one of these lowers efficiency and stretches runtime. Filter and outdoor coil rinse are yours; indoor coil cleaning is a technician’s.
Duct leaks and uninsulated ducts. Attic ducts in a 130°F attic lose a lot of cooling; leaks pull hot air into the return. Duct sealing typically pays back faster than any equipment upgrade. Duct sealing and cleaning.
Thermostat habits. Big setpoint swings, “fan on” all day (the blower is a real load, especially older PSC motors), and cooling an empty house.
Aging or oversized equipment. Efficiency drifts down over 12–15 years; an oversized system short-cycles inefficiently and doesn’t dehumidify, so people set it colder. SEER2 explained puts numbers on efficiency tiers.
Fixes ranked by payoff
- Fix aux heat settings or the underlying heat pump problem (winter): often the entire spike.
- Repair a refrigerant leak (summer): restores capacity and stops the climb.
- Filter, coil and outdoor unit cleaning: cheap, immediate, and part of an annual tune-up.
- Seal and insulate ducts, especially attic and crawlspace runs: $500–$2,500, typically 10–25% of HVAC use.
- Thermostat: smaller setbacks, aux lockout, fan on Auto, a heat-pump-aware model.
- Replace an old or oversized system: last, and only after 1–5, but in North Carolina the rebates on heat pumps can make it worthwhile sooner.
When to call
Call if the kWh rose, the weather doesn’t explain it, and the filter/thermostat/outdoor unit checks don’t find anything. Ask the technician for refrigerant charge readings, temperature split, static pressure and, in winter, a check of aux lockout and defrost. Those numbers separate the cheap fixes from the expensive ones. Every contractor on the North Carolina registry shows the license status we found.