INDIANAPOLIS GUIDE

Heat pump questions on a cold morning

Steam rising off the outdoor unit on a January morning looks like trouble. The vents may blow cool for a few minutes, the thermostat may say auxiliary or emergency, and the house is not sure which machine is in charge. Gas furnaces are common in Indianapolis, especially in older basements. Heat pumps and dual-fuel systems also exist, often where a newer outdoor unit was set beside an existing furnace, or in houses built with an air handler in a closet. Name the equipment you actually have before you decide the system has failed.

By Mike Maziarz · Sources checked October 6, 2026 · How we write these guides

Furnace, heat pump, or both

A gas furnace makes heat by burning fuel and sending warm air through the ducts. You will usually find it in a basement or a closet, with a flue or plastic vent pipes. A heat pump uses the outdoor unit to move heat. In winter it pulls heat from outdoor air. In summer it reverses and cools like an air conditioner. One outdoor cabinet can do both jobs.

Dual fuel means both are present. The heat pump handles milder cold, and the gas furnace takes over when it gets colder or the heat pump cannot keep up. The thermostat decides the handoff. If you see a furnace downstairs and a condenser outside, you may have both. Read the data plates and write both model numbers. Do not assume the outdoor unit is cooling-only.

Older houses in Meridian-Kessler and Butler-Tarkington often still have a basement gas furnace as the only heat. Newer houses toward the edge of the city are more likely to have a heat pump or a dual-fuel pair. The label on the equipment beats a guess based on the age of the street.

What defrost is supposed to look like

In cold, damp weather the outdoor coil ices up as the heat pump runs. Defrost melts that ice. The outdoor fan may stop, the unit may hiss or steam, and the indoor air can feel cool for a short stretch because the system has briefly reversed. A cloud of vapor on a cold morning is often defrost, not a fire and not a refrigerant leak by itself.

A defrost that finishes and returns to heating is normal winter behavior. A unit that stays cased in ice, a fan that never comes back, or steam mixed with a burning smell is not something to wait out. Shut the system off at the thermostat and write what you saw. Do not chip ice off the fins.

Snow and ice belong in the note. Marion County winters bring both. If a drift covers the outdoor unit, clear only what you can lift by hand without climbing on the cabinet. Leave frozen fins alone. A heat pump buried in a snowbank cannot breathe, and you can describe that from the yard.

Emergency heat is a backup, not a season setting

Emergency heat, sometimes labeled EM heat, turns on electric resistance strips or forces the backup and locks out the heat pump. It is there for a failed heat pump or a time when you need heat and the outdoor unit should not run. It is not the mode to leave selected from November through March. Auxiliary or supplemental heat is different: it can join the heat pump for a while on a cold start, then drop out.

If the thermostat is stuck on emergency and the house is warm, put it back to heat only if you know the heat pump should be primary and nothing smells wrong. If you flipped it to emergency because the house was getting cold, leave it and call. Write how long it has been in that mode. Backup heat for a day while you wait is a safety choice. Leaving it all winter because nobody explained the switch is how a surprise electric bill shows up.

What changes that bill is a cost question, not a diagnosis. The cost factors page lists what moves a quote, including backup heat, without inventing prices. Ask which mode the thermostat should use on an ordinary winter day.

When the house is actually getting cold

A heat pump that keeps up on a mild day and falls behind on an icy night may be low on capacity, low on charge, or stuck in a defrost problem. It may also be a thermostat that never calls for the furnace on a dual-fuel system. Your note should say whether the outdoor unit is running, whether the furnace burners ever light, and whether the vents are cool, lukewarm, or dead.

If the indoor temperature is still falling and people are uncomfortable, treat it as a no-heat problem for the night, not as a research project. The tonight checklist covers safe temporary steps when the house is getting cold, including when to leave emergency heat on and when a gas smell overrides everything.

Power matters. A heat pump needs electricity for the outdoor unit and the indoor blower. A gas furnace needs electricity too, even though the heat comes from fuel. In an outage, neither one heats the house. Have a plan that does not depend on the thermostat. Flashlights and a closed-off room are more useful than cycling breakers in the dark.

How the air feels with a heat pump

Heat pump supply air is often cooler to the touch than furnace air, even when the system is heating correctly. People used to a gas furnace sometimes call that a failure. Compare the vent air to the room, not to a memory of scorching registers. If the room temperature is rising, the heat pump is doing its job, even if the air at the vent is only warm.

Winter dryness and summer clamminess are separate from that. A gas furnace can make indoor air feel drier because it heats to a higher supply temperature. A heat pump may not. In July, a heat pump in cooling mode should still pull moisture out, the same job an air conditioner does. If the house is sticky or parched, the humidity guide is the place to sort filter, runtime, and what not to bolt on without a plan.

Do not block returns to make one room hotter. The heat pump needs airflow in both seasons. A closed bedroom door and a weak jump duct will make that room lag, and the thermostat in the hall will never see it.

Replacing or adding a heat pump

Swapping a furnace for a heat pump, or adding a heat pump beside a furnace, is not a filter change. It can involve electrical capacity, a new thermostat, line set, pad, and a permit. Indianapolis building permits are one office. Carmel, Fishers, Greenwood, Noblesville, and Speedway keep their own counters. The permits guide explains how to ask, without claiming that a state heating license is or is not required.

Ask any company to say, in writing, whether the proposal is repair of the heat pump you have, a dual-fuel handoff adjustment, or a full change-out. Those are different jobs. A defrost board and a new outdoor unit should not be described with the same sentence.

Keep the old thermostat instructions if you still have them. Emergency heat, auxiliary heat, and a balance point on a dual-fuel thermostat are settings, and the next technician will ask how they were left. A photo of the equipment menu is more reliable than a memory of which button you pressed on the coldest night.