Auxiliary Heat Strips: Cost Guide 2026
Auxiliary heat strip costs in 2026: per-hour cost math, lockout temperature settings, wiring mistakes that cause bill shock, and what to ask your tech.
10 MIN READ · UPDATED 2026-09-20
Key takeaways
- Aux heat strips cost roughly $1.40–$2.40/hour for a 10-kW package at typical 2026 rates — and 4 hours/day can add $200+/month; the formula is strip kW × your all-in $/kWh.
- Misconfigured lockout temperatures and thermostat wiring errors that run strips constantly are among the top causes of heat-pump bill shock.
- Set the aux lockout near your system's true balance point (commonly 25–35°F; lower for cold-climate models) — factory defaults are a frequent culprit.
- Hours of daily aux-heat runtime in mild 35–45°F weather is the red flag; check your smart thermostat's energy history or have a tech clamp-meter the strips.
- Strips are essential backup for deep cold, defrost, and emergencies — the goal is appropriate runtime (dozens of hours per winter), not zero.
If you own a heat pump and your winter electric bill ever arrived looking like a typo — double or triple the summer bill, with no change in your habits — there is a good chance you have met your auxiliary heat strips. These electric-resistance heating elements sit inside your air handler as backup heat, and they are brutally expensive to run: a single 10-kW strip package costs roughly $1.50 to $2.00 per hour at typical 2026 electricity rates, and many homes have 15 or 20 kW installed. Used correctly, strips are cheap insurance for the coldest nights. Misconfigured — wrong lockout temperatures, sloppy thermostat wiring — they run constantly and silently, and they are among the top causes of heat-pump bill shock in America.
This cost guide explains what auxiliary heat strips are, exactly what they cost per hour at your electricity rate, the lockout settings that keep them in their lane, the wiring mistakes that let them run wild, and how to tell from your thermostat whether strips are eating your budget right now.
What auxiliary heat strips are (and are not)
Auxiliary heat — “aux heat” on your thermostat — is electric-resistance heat: current through a heating element, exactly like a giant toaster. Strip packages come in 5-kW increments, commonly 5, 10, 15, or 20 kW total, sized to cover the home’s heating load if the heat pump cannot. They engage in three situations: when outdoor temperatures drop below the point where the heat pump alone can hold the setpoint (supplemental), during defrost cycles (to temper the brief cool-air episode), and in emergency mode if the outdoor unit fails.
“Emergency heat” is the manual thermostat setting that locks out the heat pump and runs the house on strips alone — appropriate during an outdoor-unit failure, ruinous as a routine setting. Some homeowners accidentally leave emergency heat on for weeks after a service visit and discover it on the bill. If your thermostat shows EM HT or similar, verify it is intentional.
The efficiency math is what makes strips expensive: resistance heat converts electricity to heat at 100% efficiency (COP of 1.0), while your heat pump’s compressor typically delivers 2 to 4 units of heat per unit of electricity. Every hour the strips carry load that the compressor could have carried costs you roughly two to four times what the heat pump would have charged for the same warmth.
What strips cost per hour: the math at your rate
The formula is simple: strip kW × your electricity rate ($/kWh) = cost per hour. Strips run at full rated power when energized — there is no modulation — so a 10-kW package draws 10 kW for every hour it runs.
| Strip size | Cost/hour at $0.14/kWh | Cost/hour at $0.18/kWh | Cost/hour at $0.24/kWh |
|---|---|---|---|
| 5 kW | $0.70 | $0.90 | $1.20 |
| 10 kW | $1.40 | $1.80 | $2.40 |
| 15 kW | $2.10 | $2.70 | $3.60 |
| 20 kW | $2.80 | $3.60 | $4.80 |
Now scale it to a month, because hours are where the damage compounds. A 10-kW package running 4 hours a day at $0.18/kWh costs about $216 a month just for the strips — on top of the compressor’s normal consumption. At 8 hours a day during a cold snap, that is over $430. And a miswired system running 15 kW nearly around the clock can add $500 to $800+ to a monthly bill, which is exactly the “typo” bill owners describe. Find your strip size on the air handler’s rating plate (or ask your tech), pull your actual $/kWh from a recent bill including delivery charges, and run your own numbers — the rate on the bill, not the advertised generation rate, is what strips actually cost you.
Lockout temperatures: the settings that prevent bill shock
Strips should be staged — brought in gradually, and only when genuinely needed. Two settings govern this, and both live in the thermostat’s installer menu or an outdoor thermostat:
Auxiliary lockout (balance point): the outdoor temperature below which strips are allowed to supplement the heat pump. Set it near your system’s actual balance point — commonly 25–35°F for standard heat pumps, lower (sometimes 10–20°F) for cold-climate inverter models that hold capacity deeper into the cold. Set the lockout too high (say 40°F on a system that heats fine at 30°F) and strips fire all winter during weather the compressor could have handled alone — the single most common configuration cause of bill shock.
Compressor lockout: the outdoor temperature below which the heat pump itself shuts off and strips (or backup furnace) take over entirely. Setting this too high strands expensive resistance heat doing a job the compressor could still do efficiently; setting it too low lets the compressor struggle inefficiently. Your installer should set both from the equipment’s performance data and your climate — not from defaults.
The uncomfortable truth: many systems were never commissioned with correct lockout temperatures. Installers leave factory defaults, thermostats get replaced without reprogramming, and homeowners inherit settings matched to nobody’s climate. If your system is more than a few years old or the thermostat was ever swapped, having a tech verify staging and lockouts during the next service visit is cheap insurance — correcting a 40°F lockout to 30°F can save hundreds per winter in cold climates.
The wiring mistakes that run strips constantly
Configuration is not the only failure mode; wiring is the other classic. The most common: the thermostat’s W (auxiliary heat) wire mislanded or jumpered so that every heating call energizes the strips alongside — or instead of — the compressor. The house stays warm, everything feels fine, and the meter spins at resistance-heat rates all winter. Owners typically discover it only when comparing bills or when a tech notices strip amperage during a routine call.
Related failure: a stuck sequencer or contactor in the air handler that keeps strips energized even when the thermostat is not calling for them — the strips run 24/7, and the first symptom is a staggering bill. And the smart-thermostat trap: aggressive setback-and-recovery programming that calls for big temperature jumps, which the thermostat satisfies by firing strips for fast recovery — a programming problem masquerading as an equipment problem, fixed with gentler setbacks and heat-pump-aware thermostat settings.
How to check: most smart thermostats show aux-heat runtime in their energy history — look for it. Aux running for hours daily in mild (35–45°F) weather is a red flag. A tech with a clamp meter can verify in minutes whether strips are drawing current when they should not be. If you suspect a problem, this is a diagnostic visit, not a parts-replacement visit — say so when booking.
When strips are the right answer
None of this means strips are the enemy. They are essential safety equipment: during genuine deep cold below the balance point, during defrost cycles, and as emergency backup when the outdoor unit fails, strips keep pipes from freezing and the house livable. A properly staged system might run its strips a few dozen hours per winter — costing tens of dollars, not hundreds — and that is exactly what they are for.
The goal is not zero strip runtime; it is appropriate strip runtime. Think of strips like the spare tire: indispensable when needed, alarming if it is doing the daily commute. If your aux-heat indicator lights up occasionally on the coldest nights, your system is working. If it is on for hours every day of a mild winter, something is misconfigured, miswired, or failing — and every week you wait is money burned at resistance-heat rates.
Reading your bill like a detective
You do not need a technician to form a strong suspicion about strip overuse — your electric bill already contains the evidence. Start with total kWh by month, which every utility bill or online portal shows. A heat-pump home’s winter consumption should roughly track heating degree days: colder months use more, milder months less, in smooth proportion. The pattern that screams strip problems is a mild winter month with disproportionately huge usage — January barely colder than December but using 60% more electricity, for example. Weather did not do that; resistance heat did.
If your utility offers hourly or 15-minute smart-meter data (most large utilities now do through their web portals), the signature is unmistakable: long, flat plateaus of very high draw — 10 to 20 kW sustained for hours — during heating periods. A healthy heat pump cycles and modulates; strips run as a flat, greedy block. Compare a plateau’s wattage against your strip package size from the air handler rating plate — if the plateau matches the strip kW, you are looking at strips carrying the load, not the compressor.
Two more checks cost nothing. First, compare this winter’s bills against the same months last year, adjusting roughly for weather severity — a sudden step-change with no lifestyle change points at equipment or configuration, not rates. Second, if you have a smart thermostat, its energy history usually breaks out auxiliary-heat runtime directly; many owners discover their “efficient” system ran aux heat for 200+ hours in a single mild month. Bring these numbers to the service visit — a tech who sees the data diagnoses in minutes what might otherwise take an hour of poking around. Screenshot the usage graphs beforehand, since some utility portals only retain detailed interval data for a year or two, and having the evidence on your phone keeps the conversation grounded in facts rather than impressions.
The other common error is subtler: thermostat settings that fight the staging logic. Aggressive “adaptive recovery” or smart-recovery features that start heating hours early can call for aux to hit a schedule deadline, and some thermostats energize strips on any setpoint change larger than 2 degrees. If your thermostat has settings for auxiliary heat droop (how far behind setpoint before strips engage), heat-pump balance point, or compressor-to-aux delay, those are the dials a tech adjusts — but knowing they exist lets you ask informed questions instead of accepting “that’s just how heat pumps work.”
Getting it fixed: what to ask your tech
Book a heating checkup with a licensed HVAC technician — ideally in fall, before the bills arrive — and ask specifically: What are my aux and compressor lockout temperatures, and are they right for this equipment and climate? Is the strip staging correct (do all kW fire at once, or in stages)? Is the thermostat wired so strips cannot run without a genuine second-stage call? And can you show me the aux-heat runtime history? A tech who answers these crisply is managing your system; one who waves them off is not.
Costs are 2026 US market ranges; get itemized local quotes. A diagnostic and reconfiguration visit is typically a standard service-call fee — modest against the hundreds per winter that misconfigured strips can cost. If strips turn out to be running constantly due to failed components (sequencers, contactors), those are inexpensive parts with straightforward labor; the expensive part was always the electricity you already burned.
Frequently asked questions
Multiply the strip package's kW by your electricity rate: a 10-kW package at $0.18/kWh costs $1.80/hour; at 4 hours/day that's ~$216/month just for strips. Find your strip size on the air handler's rating plate and use your all-in $/kWh from a recent bill (including delivery charges), not the advertised generation rate. A 15–20 kW package running constantly can add $500–$800+ to a monthly bill.
The most common causes: auxiliary lockout temperature set too high (strips allowed at 40°F on a system that heats fine at 30°F), thermostat wiring that energizes strips with every heating call, a stuck sequencer keeping strips on 24/7, or aggressive smart-thermostat setbacks triggering strip-heated recovery. Check your thermostat's aux-heat runtime history — hours of daily aux in mild 35–45°F weather is the red flag.
It's the outdoor temperature below which strips may supplement the heat pump — commonly 25–35°F for standard systems, lower for cold-climate inverter models. Set it near your system's actual balance point from the equipment's performance data, not factory defaults. Too high strands you on expensive resistance heat in weather the compressor could handle; have a tech verify it if your thermostat was ever replaced.
Only as backup: during deep cold below the balance point, during defrost cycles, and in an outdoor-unit failure. If the thermostat shows emergency heat after a service visit, verify it's intentional — some homeowners run EM heat for weeks unknowingly. Emergency heat locks out the compressor entirely, so the house heats at full resistance-heat rates until you switch it back.
Don't. Strips are safety equipment — they temper defrost cycles, carry the load in genuine deep cold, and keep pipes from freezing if the outdoor unit fails. Disconnecting them creates freeze risk and is not a code-compliant configuration. The correct fix is proper staging: correct lockout temperatures, thermostat wiring that can't energize strips without a real second-stage call, and modest setbacks. Appropriate strip runtime is dozens of hours per winter, not zero — and not hundreds.
Look for the aux-heat indicator lighting up for hours daily in mild weather, or check a smart thermostat's energy history for aux runtime. A technician with a clamp meter can confirm in minutes whether strips draw current when they shouldn't. Book it as a diagnostic visit and ask specifically about lockout temperatures, staging, and thermostat wiring — not just a generic tune-up.