What the Emergency Heat Setting Actually Does on a Heat Pump

Last January, my buddy Tyler in Fishers called me after a rough night. His heat pump had been running since 4 a.m., the house wouldn't get past 63, and he'd flipped his thermostat to 'EM Heat' thinking it meant 'extra heat.' Two weeks later, his AES Indiana bill was $380 — about double his usual — and his outdoor unit sat under a sheet of ice. He didn't need a bigger heating source. He needed to understand what the emergency heat setting actually does.

Here's the quick version: the emergency heat setting on a heat pump isn't a boost. It's a bypass. It shuts off the outdoor unit entirely and runs the backup electric resistance heat strips inside your air handler. Those strips work fine, but they're expensive to run hour after hour. In Indianapolis winters, that setting can turn a small hiccup into a $150 mistake in a week.

What the Emergency Heat Setting Actually Does

Your heat pump works by moving heat from outside to inside. Even when it's 25°F out, there's still heat energy in the air — the pump grabs it and brings it in. When the system needs a little help, it can call on auxiliary heat (AUX) automatically. AUX heat is the same electric resistance strips, but they run at the same time as the heat pump, not instead of it.

Emergency heat (EM heat) is different. When you switch your thermostat to EM Heat, you're telling the system: 'Ignore the outdoor unit. Just use the strips.' That's fine if the outdoor unit is broken or iced over. But if you switch to EM heat every time it's cold outside, you're throwing away the efficient part of your system and running on pure electric resistance — which costs two to three times more per hour.

When You Should Actually Use EM Heat in Indianapolis

Indianapolis gets real winter. We see lows in the 20s most of January, and every few years a cold snap pushes into the single digits. Homes in Carmel, Westfield, and Greenwood built in the 1980s and 1990s often have heat pumps that were sized for milder weather. When those older units hit their balance point — often around 25 to 30°F — they can't pull enough heat from the air, so the AUX strips kick in automatically. That's normal. You don't need to touch anything.

But EM heat is a manual override. You should only use it if the outdoor unit won't run at all, if the coil is encased in thick ice (not just frost), or if a technician told you to while you wait for a repair. If you're not in one of those situations, leave EM heat off.

Before you hit EM Heat, do a quick check: confirm the breaker isn't tripped, swap or clean the air filter, set the thermostat to 'Heat' (not 'Cool' or 'Auto'), and clear 12–18 inches around the outdoor unit of snow, leaves, or debris. But don't chip ice off the coil — you can punch a hole in it. If the outdoor unit is covered in thick ice and the fan won't spin, that's a service call, not a DIY project.

One thing people confuse: during normal defrost cycles, your heat pump will sometimes run the strips automatically and blow cool air for a few minutes. You might even see steam rising from the outdoor unit. That's the unit melting frost off its coil. It's not a sign you need EM heat. Switching to EM heat during defrost just makes the system run harder and cost more.

What EM Heat Costs You (And Why Your Bill Spikes)

Here's the math nobody tells you. A typical 10 kW electric heat strip uses about 10 kilowatt-hours per hour. At AES Indiana's average rate — call it $0.13 per kWh — that's $1.30 every single hour. If you run EM heat for 8 hours overnight, that's $10.40. Do that for a week, you've added $73 to your bill. And that's just the backup heat; your regular household usage is on top.

Compare that to a 3-ton heat pump running at a coefficient of performance (COP) around 2.5 in mild winter weather. It might use only 40 to 60 cents of electricity per hour to deliver the same warmth. So EM heat can be two to three times more expensive. If your heat pump is struggling, you might be tempted to 'just switch to EM and deal with it,' but that's like driving your car in first gear on the interstate — it'll get you there, but you'll watch the fuel gauge drop.

You can see more about gas vs electric heating costs in Indiana if you're weighing options. The short version: modern cold-climate heat pumps can still pull heat from 0°F air, and dual-fuel setups (heat pump plus gas furnace) mean you almost never touch EM heat. Many homeowners in Zionsville and Brownsburg have already made that switch.

How to Turn Off EM Heat (And Avoid Accidentally Leaving It On)

Once the outdoor unit is cleared of snow, repaired, or you've had a tech out, go back to your thermostat. If it's a digital display with a mode button, switch from 'EM Heat' back to 'Heat.' On some older dial thermostats, there's a separate emergency heat switch — just flip it back to normal. Then watch for AUX heat to kick in during the next cold morning. That's okay; it means the heat pump is running and the strips are assisting, not taking over.

One trick to avoid surprise AUX/EM bills: don't crank the thermostat up and down by 8 or 10 degrees. Big setbacks on a freezing night force the system to play catch-up and often triggers the backup strips. Set a steady temperature and let the heat pump do its thing. If you have a programmable thermostat, use small setbacks of 3 to 5 degrees, not 15.

A Better Long-Term Fix for Indy Winters

If you're tired of babysitting your thermostat every cold snap, the real answer might be upgrading to a dual-fuel heat pump or a properly sized cold-climate model. A dual-fuel system uses an electric heat pump down to a set temperature (like 35°F), then switches automatically to a gas furnace below that. That means no manual EM heat decisions, lower monthly costs, and consistent comfort even when it's 0°F in Plainfield or Avon.

HVACPros has helped homeowners in the Indianapolis metro retrofit older systems with heat pump conversions and dual-fuel setups. We look at your ductwork, electrical panel capacity, and the actual heat loss of your home — not just a rule of thumb — so the backup strips aren't oversized (which wastes money) or undersized (which leaves you cold). And we set the thermostat correctly from day one, so you don't have to guess.

If you're seeing ice on your outdoor unit, your thermostat keeps flipping to AUX, or you just want to know what the emergency heat setting should be on your system, let's talk. No pressure, no sales script. We'll diagnose what's going on, give you a clear written price for any repairs or upgrades, and show you how to set your thermostat for Indianapolis winters. Schedule a visit or call the office — we work across Indianapolis, Carmel, Fishers, Zionsville, Westfield, Noblesville, Greenwood, Brownsburg, Avon, and Plainfield.