Should I Use Emergency Heat? When to Switch and What It Costs

Here’s the honest answer: emergency heat has a specific purpose, and using it at the wrong time can cost you hundreds of dollars a month in higher electricity bills. But there are situations where flipping that switch is exactly the right call. Let’s walk through when to use it, when to leave it alone, and what it actually costs — in plain language, no sales pitch.

What Does “Emergency Heat” Actually Mean?

To understand emergency heat, it helps to know how your heat pump works in the first place. Unlike a furnace that burns gas or runs electric coils to create heat from scratch, a heat pump moves heat. Even when it’s cold outside, there’s still heat energy in the air. Your heat pump pulls that warmth in and pushes it into your home.

It’s an efficient process. On a mild 50°F day, your heat pump can deliver up to four times more heating energy than the electricity it uses. That’s why heat pumps save so much on energy bills compared to older systems.

But when the temperature drops into the low 30s or below, your heat pump needs help. That’s where backup heat strips come in — electric coils inside your indoor unit that generate extra warmth. Your system has two ways of using those strips, and this is where the confusion starts.

Auxiliary Heat vs. Emergency Heat — What’s the Difference?

Auxiliary heat is automatic. Your thermostat’s built-in logic monitors the gap between your set temperature and the actual temperature in your home. When that gap gets too wide — like if you bump your thermostat up by 3°F or more — the system turns on those backup heat strips alongside your heat pump to close the gap faster. It also kicks in when outdoor temps drop low enough that the heat pump needs a boost. You don’t have to do anything. It just happens.

Emergency heat is manual. When you switch your thermostat to “EM Heat,” you’re telling the system to completely shut down the outdoor unit — the compressor, the fan, all of it — and rely 100% on those backup heat strips alone. The heat pump is taken out of the equation entirely.

Here’s the key detail most people miss: the backup heat strips used for auxiliary heat and emergency heat are often the exact same physical component. The difference isn’t what heats your home — it’s whether your heat pump is also running. In auxiliary mode, the heat pump and strips work together. In emergency mode, only the strips run. And those strips are expensive to operate on their own.

When Should You Actually Switch to Emergency Heat?

Emergency heat exists for real emergencies — situations where your outdoor unit can’t run safely. Here are the scenarios where flipping that switch makes sense:

Your outdoor unit is physically damaged. If a storm knocked debris into the unit, a tree limb fell on it, or the fan blades are visibly bent or broken, switch to emergency heat immediately. Running a damaged compressor can turn a repair into a full replacement.

Your heat pump is blowing cold air and won’t stop. If you’ve waited 10 to 15 minutes and the air coming from your vents is consistently cold — not just cool during a normal defrost cycle — something is wrong. It could be a failed reversing valve, which is the component that switches your system between heating and cooling mode. Turning on emergency heat keeps your home warm while you schedule a service call.

The outdoor unit is encased in ice. A light layer of frost on your outdoor unit is normal — your system runs defrost cycles to clear it. But here in DFW, freezing rain is a different story. That heavy glaze of ice can overwhelm the defrost cycle and physically seize the fan. If you see thick ice buildup that isn’t clearing on its own, switch to emergency heat to protect the compressor from running in that choked state.

You’ve been told by a technician to use it. If an HVAC professional diagnoses a compressor issue, a refrigerant leak, or another problem with the outdoor unit and tells you to run on emergency heat until the repair is done, follow their guidance.

What Does Emergency Heat Actually Cost?

This is where it gets real. The cost difference between running your heat pump normally and running emergency heat full-time is significant — and it catches a lot of DFW homeowners off guard.

Your heat pump is efficient because it moves heat rather than creating it. For every dollar of electricity it uses, it delivers two to four dollars worth of warmth depending on the outdoor temperature. Electric resistance heat strips have no multiplier at all. One dollar of electricity in, one dollar of heat out. That’s it.

Those numbers are based on a system delivering 24,000 BTU/hr of heat at a typical DFW electricity rate of $0.15 per kWh. Even on a freezing 32°F night, your heat pump costs less than half what emergency heat costs — and on a mild day, it’s nearly four times cheaper.

Monthly Impact for DFW Homes

The total damage to your electricity bill depends on your home size and how big the backup heat strips are in your system. Here’s what it looks like for a typical DFW winter month where the heater runs six to eight hours a day:

Home Size	Strip Size	Monthly Cost (Heat Pump)	Monthly Cost (EM Heat)	Extra Cost
1,500 sq ft	10 kW	$120 – $165	$375 – $450	+$250 – $350
2,500 sq ft	15 kW	$225 – $300	$675 – $900	+$450 – $700

The worst-case scenario? Accidentally leaving your system in emergency heat mode for an entire billing cycle. We’ve seen homeowners get electricity bills over $800 and have no idea why — until someone checks the thermostat and finds it’s been running on EM heat for weeks. That’s an expensive surprise that’s completely avoidable.

Signs Your System Might Be Stuck in Emergency Heat

Sometimes the problem isn’t that you manually switched to emergency heat — it’s that your system is stuck there without you realizing it. Here’s what to watch for:

Your electric bill spiked and you can’t figure out why. If your usage jumped from 1,000 kWh to 3,000+ kWh in a single month and nothing else changed, your system may be running on strips full-time. Check your thermostat for an “EM Heat” or “AUX” indicator that stays on constantly.

Auxiliary heat runs on mild days. If it’s 45°F or 50°F outside and your thermostat is showing auxiliary heat, something is off. At those temperatures, your heat pump should be handling the load easily. This could mean low refrigerant, a failing compressor, or a defrost system that isn’t working properly.

The outdoor unit is silent. Walk outside and check. If your system is calling for heat but the outdoor fan and compressor aren’t running, the system is operating on strips only — whether you selected emergency heat or not. A thermostat relay failure can sometimes keep the emergency mode engaged even after you deselect it.

Ice that won’t go away. A thin coat of frost on the outdoor coil is normal. But if your unit has been covered in a thick layer of ice for hours and the defrost cycle hasn’t cleared it, the defrost control board or sensor has likely failed. The system will compensate by running auxiliary heat nonstop, driving your energy costs way up.

Why DFW Winters Are Different (And Why That Matters)

If you’ve lived in North Texas for any amount of time, you know the weather doesn’t do “gradual.” A 70°F afternoon can turn into a 25°F night with freezing rain in a matter of hours. Those rapid temperature swings — what old-timers call Blue Northers — create specific challenges for heat pump systems that homeowners in other parts of the country don’t deal with.

The good news is that the average DFW winter low sits between 35°F and 45°F. That’s right in the sweet spot for heat pump efficiency, where the system operates at 200% to 300% efficiency. Most of the winter, your heat pump handles everything without breaking a sweat.

The stress comes during those 5 to 10 days per year when temperatures drop below 25°F. That’s when the system leans on auxiliary heat to keep up — and that’s completely normal. It’s doing exactly what it was designed to do.

Smart Thermostat Habits That Save You Money

The most common reason for high heating bills in DFW isn’t a broken system — it’s thermostat behavior. Here are the habits that keep your costs under control:

Don’t make big temperature swings. Turning your heat down to 60°F at night and cranking it back up to 72°F in the morning creates a 12-degree gap that instantly triggers auxiliary heat. That’s an expensive way to start your day, every day, all winter.

Use the 2-degree rule. If you want to adjust the temperature, move it in 2-degree increments. Most modern thermostats will let the heat pump handle small changes on its own without calling for backup strips. It’s slower, but it’s dramatically cheaper.

Ask your technician about lockout settings. Your thermostat can be configured so that auxiliary heat won’t engage above a certain outdoor temperature — typically 35°F. This is one of the single most effective ways to prevent accidental overspending on your heating bill. If your technician hasn’t set this up, ask about it at your next maintenance visit.

Don’t rely on “Auto” mode during swing seasons. In DFW’s volatile spring and fall months, the “Auto” setting can cause your system to cycle between heating and cooling in the same day. That puts unnecessary stress on the reversing valve and wastes energy. Pick heating or cooling and stick with it until the season truly changes.

When to Call for Help (And How to Avoid Getting Oversold)

If you’ve been running on emergency heat for more than a day or two, something needs to be looked at. But here’s where a lot of homeowners get taken advantage of.

You call a company because your heat pump isn’t working. They send someone out. That person takes a quick look and tells you the whole system needs to be replaced. Maybe they quote you $8,000, $10,000, or more. And because you’re cold and stressed, you say yes without getting a second opinion.

We see this all the time. The truth is, some systems do need to be replaced. But many of the problems that force a system into emergency heat — a failed defrost sensor, a stuck reversing valve, a refrigerant leak, even a bad thermostat relay — are repairable. The difference between a repair and a replacement is proper diagnosis, not sales pressure.

At Shirley Air, that’s exactly how we work. We diagnose first. We explain what we find in plain language. And when there are options — repair vs. replacement — we lay them both out honestly so you can make the decision that’s right for your home and your budget.

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