INDIANAPOLIS GUIDE

Furnace running, but the air is cold

You turn the heat up and the blower answers. Air comes out of the register. It is not warm. In many Indianapolis houses the furnace is in the basement, beside the water heater, and this is how the first hard cold shows up. National Weather Service normals for Indianapolis, 1991 through 2020, put a typical January low near 21°F and average January snowfall at 8.8 inches, so a blower that will not deliver heat is the whole night. This page is the case where air is already moving and it is cold. A furnace that never tries to light is a different guide.

By Mike Maziarz · Sources checked October 12, 2026 · How we write these guides

Cold air is not a failed light-off

Start with the sound, because the sound sorts the call. A furnace that is blowing cold air has a blower you can hear, and often feel, at a supply vent. A furnace that will not ignite may click, glow, and go quiet, with no steady stream of air. Write which one you have before you reset anything. The ignition guide is the click-and-silence case. Stay here if the blower is already running and the air is not heating the room.

A short cooler blast at the end of a cycle is the blower finishing after the burners stop. It should end. What you are chasing is a blower that stays on while the vent never warms. Time it at one supply and at the thermostat.

A heat pump can supply milder air on purpose, and during defrost the indoor air can feel cool for a few minutes while vapor rises off the outdoor unit. That is not a gas furnace that lost its flame. If the outdoor cabinet looks like an air conditioner and the thermostat shows emergency or auxiliary heat, read the heat pump guide before you describe the system as a furnace. Say which equipment you actually have when you call.

The thermostat can do this on purpose

The thermostat can ask for air without asking for heat. Fan auto means the blower runs when the system is heating. Fan on means the blower runs all the time, including between burner cycles, and the air in the duct then feels like the basement. Set the mode to heat, set the temperature above the room reading, and set the fan to auto. Watch one cycle. If warmth shows up, the furnace was following the fan setting.

A schedule or a hold can leave the setpoint under the room temperature, so the blower you hear is not a call for heat. Copy the mode, the setpoint, the room number, and any word such as hold, wait, or auxiliary. The thermostat guide is the longer list of what the screen can be saying. Do not pull the thermostat off the wall to jump wires. That is not a check.

A packed filter and a limit trip

A filter you can slide out is a fair check. A packed filter, or one bowed out of its track, starves the furnace of air. Homeowner instructions say a dirty filter can make the furnace overheat and shut itself down. On many controls the burners stop while the blower keeps running. A troubleshooting chart for one common control says that when a limit circuit is open the blower runs until the switch closes, and it lists a dirty filter or a restricted duct among the checks. The vent air is then unheated, which on a cold day feels cold. Replace the filter only if it slides out and the size is printed on the frame. Point the arrow toward the blower, and do not run the furnace with the filter left out.

Open registers a rug has covered, and uncover the return. If the next cycle is still cold, write that down. One reset of a button you can see without removing the door is worth mentioning, if there is no gas smell. Pressing it over and over hides a lockout. The do-it-yourself boundary puts gas valves and safety switches on the technician's side.

Lockouts you can hear from the stairs

High-efficiency furnaces often have plastic intake and exhaust pipes and a drain or a small pump. The blower can still run while the burners will not stay lit. A backed-up or frozen condensate line is a common reason a condensing furnace quits on a cold night. That pattern has its own page, the frozen condensate guide. Water on the floor belongs in the note, and the leaking water guide sorts a pump from a water heater. Do not pull hoses off to test the idea.

A restricted vent can keep the burners from staying on. Snow or a nest on a sidewall pipe is visible from the yard. January snowfall in the Indianapolis normals averages 8.8 inches, enough to drift against a low pipe. Clear loose snow from the ground. Do not climb, and do not use a flame, a heat gun, or boiling water on plastic pipe. If you smell gas, leave, do not flip switches, and from outside call the emergency number on your gas bill. Many Indianapolis addresses are served by Citizens Energy Group. Citizens' gas-safety page says to leave and call from outside. Use the number on the current bill.

A carbon monoxide alarm, or a headache, dizziness, or flu-like feeling that eases outdoors, ends the troubleshooting. Get everyone outside and call emergency services. Do not keep the blower running to see if the air warms. The carbon monoxide guide is that sequence. A burning smell, or a breaker that will not stay on, is a stop as well. Leave the system off.

What to write down before you call

Say where the furnace sits: basement, closet, crawlspace, or attic. Older houses in neighborhoods such as Broad Ripple, Irvington, and Meridian-Kessler often have the unit downstairs. Say whether plastic pipes leave the cabinet and where they end on the outside wall. Say whether you saw water. Ask whether the visit includes diagnosis and what changes the scope. The cost factors page sticks to what moves a quote, without a price list.

If the house is getting cold and the people in it cannot stay warm, use the no-heat checklist for backup heat that is already safe to use, and for the point where you leave. Do not heat the house with a gas oven, a grill, or a generator. This page does not make it reasonable to jump a safety switch or tape a door shut so the blower will keep moving air.

If the visit turns into a replacement

One cold-air night is a repair conversation, not a reason to buy equipment while the house is uncomfortable. Ask what failed. If the same furnace locks out again after a real repair, the repair or replace page is how to compare a named part with a change-out, without a countdown based on age. Get the finding in writing before you accept a replacement.

If a quote replaces the heating system, read the utility page before anyone treats a credit as part of the price. Citizens Energy Group's Indianapolis conversion rebate page, separate from its Westfield list, offers existing gas customers a credit on the gas account for switching electric, oil, or propane heat to natural gas. The residential column lists $400 for a natural gas furnace. You need the gas account number, contractor information if someone else installed it, and an itemized invoice. A self-install receipt may require a home inspection. Installing a gas furnace is not a do-it-yourself project on this site.

If the electric bill is from AES Indiana and the proposal is a heat pump, the home-improvement rebate page lists amounts that require a Quality Contractor Network member. Air-source heat pumps are listed at $275, $375, or $575 by efficiency tier. Mini-split heat pumps step from $100 to $725 at the highest tier. The contractor submits the application or may take the amount off the invoice. This site is not that network and does not promise the credit. Read the efficiency table on the day you sign.