Heat Pump Electric Bill Jump in Fort Smith, AR? What the “Aux Heat” Light Means

The first real cold snap of the year hits Fort Smith, the kind where it’s in the 20s at sunrise for a few days running, and about three weeks later the electric bill lands. It’s a lot higher than last month, and a lot higher than you remember from last winter. Somewhere in there you noticed the thermostat saying “Aux Heat” more than it used to. That little word is the whole story, and understanding it is the difference between a normal winter bill and one you’re paying for nothing.

Heat pumps are everywhere in Fort Smith, especially in the all-electric subdivisions built from the eighties on and in the newer construction south of Rogers Avenue. They’re a good fit for our winters, which are cold but rarely brutal. They just need to be understood and set up right.

What a Heat Pump Does When It Gets Cold

A heat pump heats your house by pulling heat out of the outdoor air and moving it inside. Yes, even cold air has heat in it. As the outside temperature drops, there’s less heat to grab, and at some point the heat pump alone can’t keep up with what the house is losing. That’s where auxiliary heat comes in: electric heating strips inside the indoor unit that kick on to make up the difference.

The strips work, but they’re the expensive way to make heat. The heat pump compressor moves several units of heat for every unit of electricity it uses. The strips give you one unit of heat for one unit of electricity, like a giant toaster. Every hour the strips run instead of the compressor costs you a multiple of what that hour should have cost.

What the Thermostat Is Telling You

“Aux Heat” means the strips are running alongside the heat pump. Seeing it for a stretch on a 20-degree morning, or for a few minutes after you bump the thermostat up, is normal. Seeing it on a 45-degree afternoon, or on constantly for hours, is not.

“Em Heat” or “Emergency Heat” is different. That’s a manual switch that shuts the compressor off entirely and runs strips only. It exists for when the outdoor unit is broken or locked in ice. It is not a “make it warmer faster” button, and leaving it on all winter is the single most expensive thermostat mistake we see.

You may also notice the outdoor unit steaming and the air at the registers going cool for several minutes every so often. That’s the defrost cycle, and the strips run briefly during it so you don’t feel cold air. Normal, as long as it doesn’t happen every few minutes.

The Habits That Trigger Strip Heat

Pushing the thermostat up more than a couple of degrees at a time. Most thermostats call for aux heat whenever the room is more than two or three degrees below the setpoint, so going from 66 to 72 in one shot runs the strips the entire way up. Nudge it a degree at a time, or let a heat pump thermostat’s recovery feature do the ramp for you.

A deep nighttime setback. Dropping to 62 overnight and back to 70 at 6 AM saves nothing on a heat pump, because the morning recovery runs on strips. A one- or two-degree setback is as far as it should go.

A thermostat that isn’t set up as a heat pump thermostat. We find this constantly after a DIY smart thermostat install. If the thermostat thinks it’s running a furnace, it has no idea how to stage the strips, and they run far more than they should.

The Problems That Trigger Strip Heat

A dirty filter or dirty indoor coil chokes airflow, the heat pump can’t deliver its heat, and the strips cover for it. Low refrigerant charge or a dirty outdoor coil does the same from the other side. A defrost board that’s stuck keeps the unit cycling into defrost. An outdoor fan motor on its way out drops capacity. A stuck reversing valve leaves the heat pump quietly running in cooling mode while the strips do all the heating, which is the worst case for the bill.

Then there’s the one nobody suspects: a strip heat sequencer or contactor welded shut, so the strips run every time the blower runs. Including in summer. If your bill has been strange in both seasons, that’s worth checking.

Reading the Bill Like a Tech

Pull up the same month from last year and compare kilowatt-hours, not dollars, since rates change. A bill that climbed with the cold is normal. A bill that climbed with mild weather, or that jumped without a matching change in how you live, points to one of the problems above.

🛠 What we do: on a high-bill call, we check the temperature split across the indoor coil, verify the refrigerant charge, measure the amperage on each heating strip to confirm they only run when they’re called for, confirm the defrost cycle is behaving, and set the thermostat up correctly for a heat pump, including an outdoor temperature lockout so the strips can’t run on mild days. Then we tell you what we found and what, if anything, it costs to fix before we fix it.

If the System Is Old Enough to Replace

Older heat pumps lose capacity fast below freezing and lean on strips hard. Today’s inverter-driven heat pumps, which ship with R-454B refrigerant and are what Clark HVAC installs, hold their heating capacity much further into the cold and stage the strips as a last resort rather than a first. If you’re replacing a fifteen-year-old unit anyway, the difference shows up on the bill every month, and 0% financing is available on installs.

Should I switch to emergency heat when it’s really cold?

No, unless the outdoor unit is broken or frozen solid and won’t clear. The heat pump plus aux heat is still cheaper than emergency heat alone, even at 15 degrees.

Should I turn the heat down at night?

A degree or two, fine. More than that and the morning recovery eats the savings.

Do I need a dual-fuel setup?

If you have natural gas at the house, a heat pump paired with a gas furnace for the coldest hours is a strong combination here. If you’re all-electric, a modern inverter heat pump covers Fort Smith winters well on its own.

Keep the Heat Pump Doing the Work, Not the Strips

Clark HVAC is family-owned, licensed and insured, and in Fort Smith every week. If the thermostat says “Aux Heat” more than it should, we’ll find out why and give you the price before the work starts.

📞 Call Now: 918-839-3734

Straight answers. Fair pricing. Clean work.