What Is Considered an HVAC Emergency?

When your HVAC system stops working, you might wonder how serious the problem is and whether to fix it now or wait until tomorrow.

An HVAC emergency is any heating or cooling problem that puts someone’s safety at risk, threatens to damage your home, or leaves indoor conditions extreme enough that staying inside becomes unsafe. Gas leaks, carbon monoxide alarms, electrical sparks, burning smells, and a complete loss of heat or cooling during extreme weather are all examples of emergency HVAC situations that require immediate attention.

But not every HVAC issue is an emergency. A weak airflow problem, a thermostat issue, or an AC system that is struggling on a mild day may still need repair, but it usually does not require an after-hours emergency call.

In this guide, we’ll explain what constitutes an HVAC emergency, which situations require a technician, which problems can wait, and what to do during an emergency.

HVAC Emergencies That Need a Call Right Now

The situations below need an immediate response. Some are safety threats that come before any HVAC call, such as getting your family out of the house, calling 911, or contacting your gas utility. Others are comfort emergencies where timing matters because indoor conditions can become unsafe quickly.

In each case, waiting can increase the risk to your home, your equipment, or the people inside. If you are dealing with gas smells, a carbon monoxide alarm, smoke, sparks, or extreme indoor temperatures, treat the situation as urgent first, then diagnose the HVAC problem.

1. Gas Leaks

A rotten-egg or sulfur smell near your furnace, gas line, or vents is the most urgent HVAC-related issue you can have. Natural gas itself is odorless, so utilities add a chemical called mercaptan to give it that distinctive smell. If you can smell it, gas may be escaping.

Do not try to find the source yourself. Get everyone out of the house first. Leave the doors open if you can do it quickly, and do not flip light switches, start a vehicle in the attached garage, or use a phone inside the home. Once you are outside, call your gas utility. They can shut off the gas supply and confirm whether the home is safe to re-enter.

After the utility confirms the home is safe, call an HVAC technician to inspect the furnace or other gas-connected equipment. You can get gas leaks because of a loose connection, a failing gas valve, a damaged supply line, or a problem inside the furnace.

The important point is that the gas leak itself needs to be treated as an emergency. The HVAC repair comes after the immediate safety risk has been handled.

2. Carbon Monoxide Alarms or Symptoms

Carbon monoxide has no smell, no color, and no taste, which is what makes it dangerous. A working carbon monoxide detector is the only reliable warning you will get. If your detector sounds, treat it as real until proven otherwise.

The symptoms to watch for include headache, dizziness, nausea, confusion, and unusual fatigue, especially when more than one person in the home experiences them at the same time. Pets acting sluggish or sick can also be an early warning sign.

If the alarm sounds or symptoms appear, get everyone outside into fresh air. Call 911 if anyone feels sick, lightheaded, confused, or weak. If everyone feels fine but the alarm is sounding, call your gas utility or the fire department’s non-emergency line and wait for the home to be tested. Do not go back inside until someone qualified confirms that it is safe.

The HVAC cause is usually tied to a combustion appliance, such as a gas furnace or gas water heater. A cracked heat exchanger, a blocked flue, a backdrafting chimney, or a failed draft inducer can allow carbon monoxide to enter the home instead of venting outside.

These are not problems to troubleshoot while the system is still running. Shut off the system, leave the house, and have the source inspected before using the equipment again.

3. Electrical Sparks, Smoke, or Burning Smells

Sparks at the outdoor unit, smoke from the air handler, or a burning plastic smell from the vents are all signs that something may be overheating or shorting out. The main risk is fire, so the response window is short.

Turn off the HVAC system at the thermostat first. Then go to the breaker panel and shut off the dedicated HVAC breaker if you can do so safely. If you see smoke, flames, or active sparking, get out of the house and call 911 before doing anything else.

Do not restart the system to see if the problem happens again. A system that smells like burning plastic, gives off smoke, or shows signs of electrical arcing needs to stay off until it has been inspected.

Some of the most common causes are a failed capacitor, loose or burned wiring, a failing blower motor, an overheated control board, or a contactor problem in the outdoor unit. Some of these are straightforward repairs, while others may indicate larger electrical or equipment issues. Either way, the emergency is the fire risk, not the comfort issue.

If you smell a faint, dusty smell when you first run the heat in the fall, it’s usually normal. That smell comes from dust burning off after months of disuse and often clears within an hour. However, smoke, plastic-burning smells, metallic electrical odors, or any smell that persists should be treated differently.

4. Total Loss of Heat in Cold Weather

A furnace or heat pump that stops working during cold weather can quickly become an HVAC emergency. For most households, total heat loss should be treated as urgent when outdoor temperatures are around 40°F or lower, especially if the temperature inside the home is dropping fast.

The concern is not just comfort. Once a home gets cold enough, pipes near exterior walls, crawl spaces, basements, and poorly insulated areas can start to freeze. A failed heating system can lead to plumbing and water damage if the house stays cold for too long.

If someone in the home is more vulnerable to cold, treat total heat loss more urgently. Older adults, infants, pregnant occupants, and people with cardiovascular or respiratory conditions are at higher risk when indoor temperatures drop. In these households, a heating failure can be an emergency even when outdoor temperatures are only in the 40s or low 50s.

Before calling, make sure the thermostat is set to heat, the batteries are working, the air filter is not severely clogged, and the HVAC breaker has not tripped. If you have a gas furnace, check whether other gas appliances are working. If they are not, the issue may be with the gas supply rather than the furnace itself.

If the system runs but blows cold air, or if nothing comes on after those basic checks, call for service. Common emergency heating problems include a failed igniter, a dirty or bad flame sensor, a stuck gas valve, an inducer motor failure, a blower motor problem, a thermostat failure, or a heat pump defrost issue.

The exact repair matters less than the conditions inside the home. If the house is becoming unsafe or the plumbing is at risk, it is an emergency.

5. Total Loss of Cooling in Hot Weather

A broken AC is not always an emergency, but a complete cooling failure during extreme heat can make a home unsafe, especially in humid climates where the heat index makes indoor conditions feel worse.

For most households, total AC failure should be treated as urgent when outdoor temperatures are around 90°F or higher, or when indoor temperatures climb into the mid-80s and keep rising. In places like Greenville, a home without AC in July can become uncomfortable fast and unsafe for some people within hours.

Vulnerable household rules apply here, too. Older adults, infants, pregnant occupants, people with heart or lung conditions, and anyone taking medications that affect heat tolerance are more likely to struggle when indoor temperatures rise. If someone in the home is already feeling weak, dizzy, nauseous, confused, or overheated, treat the situation as an emergency.

While waiting for service, close blinds on the sunny side of the house, run ceiling fans, drink water, and move everyone to the lowest and coolest level of the home. Avoid using the oven, dryer, or any other heat source indoors.

Before calling, check the thermostat, breaker, air filter, and outdoor unit. If the indoor blower is running but the outdoor unit is silent, the problem may be electrical, such as a failed capacitor or contactor. If the system is running but blowing warm air, possible causes include a frozen evaporator coil, a refrigerant leak, a compressor issue, or an airflow restriction.

If you see ice on the refrigerant lines or the indoor coil, turn the system off. Running the AC longer will not make the home cooler and can make the problem worse.

6. Refrigerant Leaks

A refrigerant leak is not always a same-hour emergency, but it should not be ignored. Signs of a possible leak include weaker cooling, longer run times, ice on the copper refrigerant lines or evaporator coil, a hissing or bubbling sound near the indoor or outdoor unit, and sometimes a faint sweet or chemical smell.

If you notice any of these signs, turn the system off at the thermostat. Low refrigerant can cause the evaporator coil to freeze and can put extra strain on the compressor. Continuing to run the AC may turn a repairable leak into a much more expensive system problem.

Refrigerant is not something a homeowner can safely refill or repair. A technician needs to find the leak, repair it if possible, and recharge the system to the correct level. Recharging the system without finding the leak is a red flag. Refrigerant does not get “used up,” so a system that needs more refrigerant has a leak somewhere.

The emergency level depends on the situation. If the AC is still cooling somewhat and the weather is mild, the repair may be able to wait for a normal appointment. If the system has stopped cooling during extreme heat, the home is becoming unsafe, or someone inside is vulnerable to heat, treat it as an emergency cooling call.

A major refrigerant leak in an enclosed space can also create health concerns. If you notice a strong chemical smell, hear active hissing, or feel dizzy, lightheaded, or short of breath near the system, leave the area, ventilate it if you can do so safely, and call for professional help. Older systems using R-22 can also be more expensive to repair because that refrigerant is no longer manufactured in the United States.

Here’s a tightened version of the full section, keeping the same points but making it read more like the earlier parts.

7. Active Water Leaks From the System

Some water around an HVAC system is normal. A working AC produces condensate, and that water usually drains through a PVC line that exits the side of the house. A few drips at the outdoor end of that line on a humid day is not a problem. Active water pooling near the indoor unit, dripping from a ceiling, or running down a wall is different.

The most common cause is a clogged condensate drain. Algae and debris can build up in the drain line over time, causing water to back up into the drain pan and overflow. Many modern systems have a float switch that shuts the AC off when this happens, but older systems may keep running until someone notices the leak.

Other possible causes include a cracked drain pan, a failed condensate pump in an attic or basement installation, or a frozen evaporator coil that has thawed and overflowed.

Turn the system off at the thermostat as soon as you notice the leak. If water is near the air handler, a junction box, or any electrical component, shut off the HVAC breaker too. Move valuables away from the wet area and place a bucket under any active drip.

A small condensate issue may not be a safety emergency, but it can quickly become a property damage emergency. If water is leaking through a ceiling, spreading across the flooring, or near electrical equipment, call for service right away.

8. Strange Noises That Mean Something Is Failing

HVAC systems make some noise during normal operation. A soft hum from the outdoor unit, a quiet click when the system starts, and gentle airflow through the vents are usually normal. Loud, sharp, metallic, or new sounds deserve more attention.

Grinding from the outdoor unit can point to a failing compressor bearing or motor. If the system keeps running, the damaged part can fail completely and may damage surrounding components. Shut the system off and call for service.

Screeching or high-pitched squealing from the indoor or outdoor unit often points to a belt problem in older systems or a bearing issue in newer ones. The sound itself may not be the emergency, but it is often a warning that a motor or moving part is nearing failure.

Banging or loud metallic clanking can mean something has come loose inside the blower assembly or outdoor fan. A loose blower wheel or fan blade can repeatedly strike the housing, causing serious damage quickly. Shut the system off immediately.

Repeated loud clicking from a furnace during a heating cycle, especially if the system tries to start several times and then locks out, can point to an ignition problem. The furnace has safety controls that should shut it down if ignition fails, but the underlying issue still needs a technician.

As a rule, any HVAC noise that sounds like grinding, screeching, banging, or metal hitting metal should be treated as urgent. Turn the system off and do not restart it until it has been inspected.

9. Frozen AC Coil or Iced-Over Outdoor Unit

Ice on an HVAC system usually means something has gone wrong. Air conditioners and heat pumps move heat, and ice forms when that process is disrupted.

In summer, ice on the indoor evaporator coil or copper refrigerant lines can point to low refrigerant, a dirty air filter, restricted airflow, a failed blower motor, or closed vents. The system may keep running, but the ice will usually get thicker, cooling will get worse, and the compressor can be damaged if the problem continues.

Turn the system off at the thermostat as soon as you notice ice. Do not keep lowering the temperature to make it cool faster. Let the system thaw completely, then check the filter and replace it if it is dirty. Once the ice has melted, you can try cooling again.

If ice forms a second time within a day, call for service. The underlying problem will not fix itself, and continuing to run the system can lead to a much more expensive repair.

In winter, a thin layer of frost on a heat pump’s outdoor unit can be normal. The defrost cycle should clear it during cold, damp weather. But if the outdoor unit is completely encased in ice, or if frost stays on the unit for hours without clearing, the defrost cycle may have failed.

Common causes include a failed defrost board, a stuck reversing valve, a bad outdoor temperature sensor, low refrigerant, or an outdoor fan problem. A frozen heat pump is not always an immediate safety emergency, but it should be addressed quickly before the system loses heating capacity or moves into expensive auxiliary heat.

10. Heat Pump Stuck in Auxiliary Heat or Emergency Heat

Heat pumps are common across the Southeast, including many homes in the Upstate. When they work properly, they heat efficiently by pulling heat from the outdoor air. When something goes wrong, the home may still stay warm, but the system can become much more expensive to run.

A heat pump has two ways to heat a home. The compressor provides efficient heat. When outdoor temperatures drop too low for the compressor to keep up, electric resistance heat strips inside the air handler turn on as backup. These heat strips are meant to run occasionally during cold snaps, not constantly.

The warning sign is an “Aux Heat” or “Emergency Heat” message on the thermostat that stays on for an extended period, especially if your electric bill has suddenly doubled or tripled. This can mean the heat pump is not heating properly, and the backup heat strips are doing most of the work.

Common causes include a failed reversing valve, a refrigerant leak, a frozen outdoor unit, a defrost issue, an outdoor fan failure, or a compressor problem. The repair is not always urgent in terms of safety if the home is still warm, but it can quickly become a financial emergency.

If your thermostat has stayed in Aux Heat or Emergency Heat for more than a day, or if your bill suddenly spikes with no clear weather explanation, call for service. The sooner the heat pump issue is diagnosed, the less time the system spends relying on expensive backup heat.

HVAC Issues That Are Not an Emergency

Most HVAC problems are not emergencies. They are real issues that need attention, but they can usually wait until normal business hours if they are not putting anyone at risk, causing active damage, or making indoor conditions unsafe. If you are calling outside business hours for the situations below, you often pay an after-hours surcharge for a repair that would cost the same during a regular service call.

• Dirty air filter or weak airflow: A clogged filter is one of the most common causes of weak airflow, short cycling, and frozen coils. Replace the filter, give the system time to recover, and see if airflow improves. If airflow is still weak after a filter change, schedule a regular service call.
• Mild rattling, humming, or vibration: New sounds are worth paying attention to, but a soft rattle or low hum with the system still heating or cooling normally is rarely urgent. A loose access panel, backed-out screw, or small piece of debris near the outdoor fan grille can cause minor noise. Tighten what you can safely see and schedule a tune-up if the sound continues.
• Higher-than-normal energy bill: One unusually high bill usually points to weather, thermostat changes, or heavier-than-normal usage, not an emergency system failure. If bills stay high for two or three months, schedule maintenance to check refrigerant levels, blower performance, ductwork, and overall system efficiency.
• One room warmer or cooler than the rest of the house: Uneven temperatures usually come from airflow imbalance, duct issues, insulation gaps, sun exposure, or closed vents. These problems can be frustrating, but they are not emergency repairs. A technician can check ductwork, airflow, and system balance during a scheduled appointment.
• System struggling on an extreme weather day: An AC that cannot pull a 95°F day down below 78°F, or a furnace that struggles during a hard freeze, may be operating at the edge of its capacity. Older systems, undersized equipment, poor insulation, and duct leakage can all make this worse. It is worth diagnosing, but it is not an emergency unless indoor conditions become unsafe.
• Area-wide power outage: If the power is out, the HVAC system will not run. This is a utility issue, not an HVAC issue. Do not call an HVAC technician for a neighborhood power outage. When power returns, wait a few minutes before turning the system back on at the thermostat to reduce the risk of damage from a voltage surge.
• Routine maintenance is overdue: A system that has gone two or three years without a tune-up is more likely to break down, but overdue maintenance by itself is not an emergency. Schedule a maintenance visit before the next peak heating or cooling season.
• Faint dusty smell when the heat first turns on: A mild dusty smell when you first run the heat in the fall is usually normal. Dust burns off after months of disuse, and the smell often clears within an hour. If the smell lasts longer, smells like burning plastic, or comes with smoke, shut the system off and treat it as an emergency.

If you are unsure whether your situation belongs in this list or the emergency list above, ask yourself these three questions:

• Is anyone in immediate danger?
• Is the system causing damage right now?
• Will indoor conditions become unsafe before morning?

If the answer to all three is no, the issue can usually wait until normal business hours.

What to Do During an HVAC Emergency

The first few minutes of an HVAC emergency matter more than most people realize. Done right, they keep your family safe, prevent further damage to the system, and shorten the time a technician spends diagnosing the problem once they arrive. Done wrong, they can turn a $400 repair into a $4,000 one or, in the case of gas and carbon monoxide, put lives at risk.

Here is what you should do when you have an HVAC emergency:

• Get everyone out first if there is a safety risk. If you smell gas, hear a carbon monoxide alarm, see smoke, notice sparks, or someone feels dizzy, weak, confused, or nauseous, leave the house first. Do not stay inside trying to inspect the furnace, reset the thermostat, or find the source of the problem.
• Do not keep running a system that seems unsafe. If the system smells like burning plastic, makes grinding or banging noises, leaks water near electrical parts, has visible ice, emits smoke, or repeatedly shuts down, turn it off and leave it off. Restarting the system to “see if it still happens” can turn a repairable problem into a major failure.
• Call 911 first if there is a fire, smoke, active sparking, carbon monoxide symptoms, or anyone in immediate danger. In those cases, the emergency is bigger than the HVAC system. Get outside, call for emergency help, and do not go back inside until the home has been cleared.
• Call your gas utility first if you smell gas. Do not flip light switches, use a phone inside, start a car in an attached garage, or unplug appliances. Leave the house, move to a safe location, and call your gas utility from outside. Call an HVAC technician only after the utility confirms the home is safe to enter.
• Shut the system off if it is safe to do so. For burning smells, loud mechanical noises, ice buildup, or active water leaks, turn the HVAC system off at the thermostat. If water is near the air handler, wiring, a junction box, or any other electrical component, shut off the HVAC breaker as well. Do not touch standing water near electrical equipment.
• Check only the simple things. Once the immediate safety risk is handled, check the thermostat setting, thermostat batteries, air filter, HVAC breaker, and whether the outdoor unit is blocked. If you have a gas furnace, check whether other gas appliances are working. Do not remove panels, test wires, relight pilot lights repeatedly, or keep resetting a system that shuts down on its own.
• Protect the home from damage while you wait. If water is leaking, move furniture, rugs, boxes, and valuables away from the wet area. Place a bucket under the active dripping if you can do so safely. If the heat is out during freezing weather, open cabinet doors under sinks, keep interior doors open, and let vulnerable faucets drip slightly. If the AC is out during extreme heat, close the blinds, run the ceiling fans, avoid using the oven or dryer, drink water, and move everyone to the lowest, coolest part of the home.
• Give the technician clear information when you call. Explain whether the system is heating, cooling, or completely off. Mention any smells, sounds, smoke, sparks, water, or ice. Share the indoor and outdoor temperature, whether anyone in the home is vulnerable to heat or cold, what you have already checked, and how long the problem has been happening.

If the HVAC system poses a safety risk, is causing active damage, or makes the home unsafe to stay in, stop using it and call for help. If none of those things are happening, the issue can usually wait for a normal appointment.

When in Doubt, Make the Call

A dirty filter, a mild airflow issue, uneven room temperature, or a routine maintenance concern is inconvenient but usually not dangerous. The situations that cannot wait, like gas leaks, carbon monoxide alarms, electrical sparks, no heat in a cold snap, or no cooling during a heat wave, all share one thing in common: every hour you wait can increase the risk, the damage, or both.

Air Today has answered emergency HVAC calls across the Upstate since 1981. Our phones are staffed by a local team, not a national call center, and a technician can be dispatched quickly for genuine emergencies in Greenville, Greer, Simpsonville, Mauldin, Easley, and the surrounding areas. We will also tell you honestly when your situation can wait until business hours, so you do not pay an after-hours surcharge when you do not need to.

If you are dealing with an HVAC emergency in the Upstate, call us immediately. We answer the phone around the clock, and a technician can be at your door within the hour.