Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
Three HVAC situations are genuine emergencies: a carbon monoxide alarm sounding, a gas smell, or any burning smell or smoke. In those, leaving the building comes before calling anyone.
Everything else, including no heat in winter and no cooling in a heatwave, is urgent rather than dangerous for most households, and becomes an emergency when the temperature threatens vulnerable people or the building.
Stop and leave: the three real emergencies
These are not service calls in the ordinary sense. Get out first, then call from outside.
- A carbon monoxide alarm sounds. Get everyone outside into fresh air, then call the fire service or 911. Do not go back in to investigate. CPSC estimated 274 non-fire carbon monoxide deaths from consumer products in 2022, and 76 of them, 28%, involved heating systems.
- You smell gas. Do not operate switches or appliances. Leave, then call the gas utility’s emergency line from outside.
- Burning smell, smoke or soot. Shut the system off at the thermostat and the breaker if you can do it safely, then leave and call.
CPSC’s guidance for the prevention side is a “yearly professional inspection of all fuel-burning home heating systems, including furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents.”
Urgent, but not an evacuation
These justify an out-of-hours call, and they are what most emergency HVAC services actually attend.
| Situation | Why it is urgent | What to do first |
|---|---|---|
| No heat, freezing outside | Risk of burst pipes and cold exposure | Check thermostat, breaker, filter, gas supply; keep taps trickling |
| No cooling in extreme heat | Heat illness, especially for older adults, infants, the ill | Move to a cooler space, check breaker and filter, use fans |
| Water pouring from the indoor unit | Property damage | Shut the system off, clear the condensate drain if accessible |
| Electrical burning smell, no smoke | Component overheating | Shut off at the breaker, call |
| Outdoor unit humming, not starting | Motor can overheat | Switch off at the thermostat; likely a capacitor or contactor |
That last one is one of the most common after-hours calls. See what a capacitor does and what HVAC noises mean.
Check these before you pay an out-of-hours rate
A meaningful share of emergency calls end in something the owner could have checked in two minutes.
- Thermostat. Mode, setpoint, batteries, and whether it is calling for heat or cooling at all. See how thermostats work.
- Breaker and outdoor disconnect. Reset a tripped breaker once. If it trips again, stop and call.
- The filter. A blocked filter causes no-heat lockouts on the heating side and frozen coils on the cooling side. See why an AC freezes up.
- The furnace door switch. A panel not seated will stop a furnace completely.
- Gas supply. Other gas appliances working tells you the supply is on.
If the furnace is trying to light and failing, the ignition sequence page explains what the pattern of clicks and pauses is telling you.
Out-of-hours work is priced for the visit, not the fix. Parts availability at 2am is the real constraint, and many night calls end in a temporary measure with the repair completed the next working day. Ask what the call-out fee covers, whether it is credited against the repair, and whether the part is on the van, before agreeing to the visit.
If you cannot get heat tonight
Two safety points matter more than comfort, and both appear in CPSC’s heating guidance: never heat a home with a cooking appliance, and never run a generator or any engine-driven tool indoors or in an attached garage. Engine-driven tools were associated with the largest share of carbon monoxide deaths in CPSC’s 2022 estimates, 39% of the total, with generators the main contributor.
Frequently asked questions
What counts as an HVAC emergency?
A sounding carbon monoxide alarm, a gas smell, or smoke and burning smells are true emergencies: leave the building first and call from outside. No heat in freezing weather, no cooling in extreme heat, and water damage are urgent and justify an out-of-hours call, but are not evacuations.
What should I do if my heat goes out in winter?
Check the thermostat mode and batteries, the breaker, the filter and the furnace door panel, and confirm other gas appliances work. Keep taps trickling to reduce the risk of frozen pipes. Never heat the house with a cooking appliance or run a generator indoors.
Is no air conditioning an emergency?
It can be, depending on who is in the house. Extreme heat is dangerous for older adults, infants and people with medical conditions. For most households it is urgent rather than an emergency: move to a cooler space, run fans, and check the breaker and filter first.
Is emergency HVAC service more expensive?
Generally yes, through an out-of-hours call-out fee. No federal source measures HVAC pricing. Ask what the fee covers, whether it is credited against the repair, and whether the likely part is on the van, since many night visits end in a temporary fix.
Methodology and limitations
Carbon monoxide figures are CPSC 2022 annual estimates, published May 2026. Safety guidance is quoted or summarised from CPSC’s home heating equipment materials.
- We publish no emergency call-out prices, because no federal source measures them.
- CPSC estimates cover consumer products under its jurisdiction and are revised in later reports.
- This page is general guidance, not instructions for a specific appliance or a medical situation.
Sources
- US Consumer Product Safety Commission, Home Heating Equipment.
- US Consumer Product Safety Commission, Non-Fire Carbon Monoxide Deaths Associated with the Use of Consumer Products, 2022 Annual Estimates, published May 2026.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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