Gas smell or a CO alarm: leave the house first. For anything else, pick the symptom and see how fast it needs a technician.
Leaveif you smell gas or the CO alarm is soundingThen call your gas utility or 911 from outside. HyreHVAC is not an emergency service and does not send technicians.
The short answer
If you smell gas, a carbon monoxide alarm is sounding, or equipment is smoking, leave the house and call your gas utility or 911 from outside.
For a burning electrical smell, ice on the lines or a water leak, switch the system off and call. No heat when pipes can freeze is urgent. No cooling usually is not, unless someone at home is at risk from heat.
What is happening right now?
If you can smell gas or the CO alarm is sounding, leave before you finish this form.
—Urgency
—What to do
—Then
What this assumed
—
If you smell gas or a CO alarm sounds, leave the house and call your gas utility or 911 from outside.
When should you leave the house instead of calling for HVAC service?
A carbon monoxide alarm sounding: Get everyone outside into fresh air, then call 911 from outside. Do not open windows first, do not look for the source, and do not silence the alarm and go back to bed. CO has no smell or color. The alarm is your only warning.
A smell of gas: Leave the house and call your gas utility or 911 from outside. Do not use light switches, thermostats or phones inside, because a spark can ignite the gas. Every gas utility runs an emergency line, staffed around the clock and free to call.
Smoke, burning smells or visible flame from equipment: Switch off the power at the breaker if you can do it safely on your way out. Then leave and call 911 from outside.
These are not calls for an HVAC contractor. Being hot or cold is not an emergency in this sense, however uncomfortable. The triage below keeps the two apart.
How urgent is each HVAC problem?
Situation
Urgency
What to do
CO alarm, gas smell, smoke or flame
Emergency services
Leave the building. Call from outside. Do not investigate
No heat, outdoor temperature below freezing
Call today
Real risk to pipes and to vulnerable people at home. Use the contractor’s emergency line
No cooling in a heat advisory, vulnerable occupant
Call today
Heat is dangerous to infants, older adults, and people on some medications
No cooling in a heat advisory, healthy adults
Urgent, not an emergency
Cool the body rather than the house. Move to a cooler building if you can
Worth a diagnostic visit. Often a developing and correctable fault
Sorted by urgency. Only the top row is not a call to a contractor.
Where the choice is between heat exposure and no cooling, the priority is cooling the people rather than the building. A cooler public building nearby beats waiting at home for a technician.
Who is most at risk when the AC fails?
Households under strain when cooling fails, 2020: Association, not causation. Households without cooling are poorer on average.HyreHVAC calculation from EIA RECS 2020 microdata. The full study →
Whether it is an emergency depends more on who is in the house than on the equipment. The EIA Residential Energy Consumption Survey is the closest federal measure of that.
4.5% of American households went without cooling at some point because their equipment was broken. Among households with no cooling at all, 11.8% reported keeping their home at a temperature they considered unhealthy — against 9.8% of households with cooling. 25.7% went without food or medicine to pay an energy bill, against 19.2%.
HyreHVAC analysis: read these as linked, not cause and effect. Households without cooling are poorer, and poverty drives both answers. The point that matters here: the homes most likely to lose cooling are the least able to pay an emergency call-out fee.
If that is you, say so when you call. Many utilities and local agencies run heat-emergency assistance programs, and contractors often schedule differently for a household with a medical need.
One figure we will not give you: RECS asks whether anyone in the household needs cooling for a medical reason, but among households without cooling that estimate carries a relative standard error of 32% — above EIA’s own 30% suppression threshold. It would have made a strong headline and the survey cannot support it.
What should you check before calling an HVAC company?
Batteries, mode, and whether a schedule or a hold has been set by somebody else in the house. A surprising share of no-heat and no-cool calls end here, at the cost of a call-out fee.
The breaker and the outdoor disconnect
Check the panel and the disconnect switch beside the outdoor unit. If a breaker has tripped, reset it once. If it trips again, stop and call. Repeated tripping is a fault, not a nuisance.
The filter
A filter left long enough restricts airflow badly enough to ice a coil or trip a limit switch. It is the cheapest possible fix and the most commonly missed one.
Systems with a float switch shut down deliberately when the drain backs up. That is the system protecting your ceiling, and clearing the drain often restores it.
Return grilles and vents
Furniture or a rug over a return starves the system of air as effectively as a blocked filter, and it is free to fix.
Do not open the refrigerant circuit
Federal law requires EPA Section 608 certification to open a refrigerant circuit or to buy refrigerant, including R-410A since 2018. Nothing in the checks above involves it.
What should you do while you wait for a technician?
Situation
Do
Do not
No cooling in extreme heat
Close blinds on sun-facing windows, use fans to move air across skin, drink water, move to the coolest room or a cooler building
Do not rely on a fan alone above about 95°F. Moving hot air over skin stops helping
No heat in freezing weather
Close off unused rooms, open cabinet doors under sinks on exterior walls, let taps drip, use layers and blankets
Do not use an oven, a gas range or an outdoor heater indoors. This is how CO poisoning happens
Water leaking indoors
Switch the system off at the thermostat and the breaker, contain the water, check the condensate drain
Switch to fan-only to thaw, then replace the filter and check the returns
Do not chip the ice off, and do not keep running it in cooling
Vulnerable occupant, no conditioning
Call the utility and local agencies about heat or cold emergency assistance, and say so when booking the contractor
Do not wait it out on the assumption that it is just discomfort
Practical steps between the call and the visit.
The single most dangerous item on this page is using an oven, a gas range or an unvented outdoor heater to heat a room. It is a common improvisation in a cold snap and it is a recognized cause of carbon monoxide poisoning.
What can this triage not do?
The triage is not a medical assessment
If someone has symptoms of heat illness or CO exposure, such as confusion, headache, nausea or dizziness, call 911. That is not a decision about an appliance.
It cannot diagnose the fault
This sorts urgency, not cause. Two systems with identical symptoms can have entirely different faults behind them.
Local emergency thresholds vary
What counts as a heat or cold emergency depends on your climate, your building and who lives there. A 95°F day is routine in Phoenix and a public health event in Seattle, where most homes have no cooling at all.
A CO alarm is not optional equipment
Every home with a fuel-burning appliance or an attached garage should have working CO alarms. If this page prompts one action, make it that one.
Repeated deliberately
When does nothing on this page apply? Gas, CO, smoke or flame
A gas smell, a sounding carbon monoxide alarm, smoke, or flame. For all four, leave the house and call your gas utility or 911 from outside. None of them is an HVAC booking.
Leave the house and call your gas utility or 911 from outside: For a gas smell, call the gas utility’s emergency line or 911. For a CO alarm, smoke or flame, call 911.
Do not use light switches, thermostats or phones inside a house where you can smell gas, because a spark can ignite it.
Do not open windows first, do not look for the source, and do not silence a CO alarm and go back to bed. Carbon monoxide has no color or smell. The alarm is your only warning.
We repeat this here because someone reading at two in the morning may not start at the top. Every other section on this page assumes those four situations have been ruled out.
HyreHVAC analysis: the most dangerous thing after an HVAC failure is often the fix people improvise: heating a room with an oven, a gas range or an unvented outdoor heater in a cold snap.
It is a recognized cause of carbon monoxide poisoning. It is also why the triage table says to call today about no heat in freezing weather.
The useful next step: if the house has a fuel-burning appliance or an attached garage and no working carbon monoxide alarm, buy one before anything else on this page. It is the cheapest fix on this site, and the only one that addresses a fatal risk.
Is it an emergency? It depends on who is at home
The same failure in two identical houses is not the same event. A compressor that stops on a 98°F afternoon is an expensive nuisance for healthy adults. For an infant, an older adult, or someone on a medication that affects body temperature, it is a real medical risk.
Source fact: 4.5% of American households went without cooling at some point because their equipment was broken. That national estimate from the EIA Residential Energy Consumption Survey shows a breakdown is an ordinary event, not a rare one. That is why calling it an emergency is so useful to whoever answers the phone.
HyreHVAC analysis: the question that predicts harm is "who is in the house and can they leave", not "how hot is it". A healthy adult can cool their body instead of the building. Use a fan below about 95°F, drink water, take a cool shower, or spend the afternoon at a library or cooling center.
Someone with limited mobility, an infant, or a person who cannot be moved has none of those options. For that household, calling for help right away is the right call.
The same inversion applies in winter. No heat at 45°F is uncomfortable. No heat at 15°F is a burst-pipe risk to the building and a hypothermia risk to a vulnerable occupant, and the pipe risk alone justifies calling that day, whoever is home.
The useful next step: when you call, say who is in the house. Many contractors schedule differently for a household with a stated medical need, and many utilities and local agencies run heat and cold emergency assistance programs. Neither happens if nobody knows to ask, and neither costs you anything to raise.
What does waiting cost, symptom by symptom?
The triage table above sorts by urgency to people. This one sorts by what happens to the equipment, which is a different question and occasionally the more expensive one.
Symptom
What is happening mechanically
What waiting risks
What its absence tells you
Ice on the suction line or coil
The coil is running below freezing because airflow is restricted or the charge is low, so condensate freezes instead of draining
Liquid refrigerant reaching a compressor built to receive vapor. This is the failure a compressor does not survive, and it converts a filter or a charge problem into a replacement
If the coil is clear and the system still is not cooling, the fault is elsewhere. That rules out the two most common causes
Breaker tripping repeatedly
A protective device is interrupting a circuit drawing more current than it should
Repeated resetting defeats the protection. The breaker is the part working correctly
A breaker that holds after one reset points at a transient rather than a fault, though it is still worth mentioning at the next visit
Water at the indoor unit
Condensate is not reaching the drain: usually a blocked line, sometimes a failed pump
Ceiling and structural damage, which routinely costs more than the HVAC repair that caused it
A float switch that has shut the system down deliberately is the system protecting your ceiling. Its absence is why some systems flood instead of stopping
Hard starting, or a hum with no fan
Often a run capacitor that drifted out of tolerance. It is a wear part that fails on healthy systems
Little, mechanically, but it strands you on the hottest day. The part is inexpensive; the after-hours visit to fit it is not
A system that starts cleanly every time is not building toward this particular failure
No heat, freezing outside
Any of a dozen faults, from a flame sensor to a control board
Frozen pipes. The building risk applies whoever is home, which is why this row says call that day
A house that holds temperature for many hours has thermal mass on its side and buys you the morning
Higher bills, no other symptom
A developing fault degrading efficiency without stopping the system
Very little in the short term. This is a routine diagnostic visit, and it is where the 70-90% fault-prevalence figure actually lives
Bills that track the weather and nothing else suggest the system is doing what it always did
Sorted by how much the machine loses by waiting, which is not the same ordering as how much the household does.
Only two rows here justify an after-hours call on equipment grounds alone: ice on the lines, because the damage compounds while it runs, and water, because the damage is to the building. Both can be stopped by switching the system off, which is free and buys you until morning.
Why do after-hours HVAC calls cost more?
Illustrative only: The three parts of an after-hours invoice, drawn to show the shape of the decision rather than any measured proportion.HyreHVAC illustration. We hold no invoice data and publish no cost figures.
Because it costs more to supply. A technician is paid extra to leave home at eleven at night, and the van carries what it carries, not the part your system needs. A premium is not a scam. It is the price of unscheduled service.
HyreHVAC analysis: the catch is when you decide. It is usually at night, hot or cold, under stress, with someone on the phone who wants the van rolling now. The premium is fair. The moment you agree to it is a poor one for judgment, so ask two questions before you say yes.
The useful next step, in two questions: First: what is the call-out fee, and is it applied to the repair if I go ahead?
Second: what is the after-hours labor rate, as against the standard rate? Both have number answers and should be given without hesitation.
If either is dodged, you learn that before the van is sent.
A third question is worth asking whenever the situation allows it: can this wait until the morning? A contractor who honestly says it can (and many will) has told you something worth more than a discount.
Source fact, on who is permitted to do the work: If the fault turns out to involve the refrigerant circuit, 40 CFR Part 82, Subpart F under Section 608 of the Clean Air Act requires the technician to hold Section 608 certification.
Residential split-system work is high-pressure work, which means Type II or Universal. This is federal and identical in every state, unlike the licensing rules, which vary by jurisdiction and are not comparable across state lines.
Illustrative chart. HyreHVAC does not install, service or sell HVAC equipment, and holds no data on quotes, invoices or finished jobs. Nothing here is a price we observed. That is also why these tools can tell you to keep the system you have.
The proportions above are drawn to make the structure of an after-hours invoice visible and should not be read as data. The two questions in the text are the part of this section with real content.
How old is the system, and why does that matter at 2 a.m.?
Age of home cooling equipment, 2020: Shares of households with cooling equipment, weighted to the national population.HyreHVAC calculation from EIA RECS 2020 public use microdata. The full study →
Source fact: 9.6% of American households with cooling equipment have equipment twenty years old or more, and a further 10.1% are in the fifteen-to-nineteen band. Meanwhile 27.5% sit in the five-to-nine band, the largest single group and the flattest part of the risk curve.
HyreHVAC analysis: your system’s age should change how you hear "it needs replacing" at midnight. On an 18-year-old system that may well be right. On a six-year-old system it needs daylight, a second opinion and the readings behind it, none of which you get in the middle of the night.
The useful next step: if a replacement is proposed during an emergency visit, ask for the repair that gets you through the night or the week.
Then get the replacement quoted properly by more than one contractor. A working system is no longer an emergency, and you decide better outside one.
The exception is a cracked heat exchanger or any finding with a combustion-safety dimension. If a technician red-tags a furnace on safety grounds, that is not a commercial judgment to be shopped around, and the system should stay off until it is resolved.
RECS records equipment age but not failure events, so this chart establishes the age profile of the installed base and not a failure rate. We are not able to publish a failure rate by age, because no public dataset we could find supports one.
What should you have ready before you call?
Two minutes of preparation shortens the visit, and on an after-hours rate the length of the visit is most of the invoice.
The make, model and serial number from the data plate
On the outdoor unit and on the indoor unit or furnace. It lets a dispatcher check whether the likely part is on the van, which is the difference between one visit and two.
Roughly how old the system is
Often encoded in the serial number, often printed outright, sometimes on a permit sticker or an old invoice. It changes the whole conversation, particularly if a replacement is going to be proposed.
What you already checked
Thermostat, breaker, disconnect, filter, return grilles, condensate drain. Saying so up front stops the visit starting from zero, and occasionally ends the call before the van leaves.
Exactly what changed, and when
"It stopped cooling on Sunday and the breaker has tripped twice since" is diagnostic information. "It is not working" is not. Note whether the outdoor fan runs, whether the indoor blower runs, and whether there is any noise that is new.
Whether anyone in the house is vulnerable to heat or cold
Say it explicitly. It affects scheduling with many contractors and it is the fact most likely to move you up a queue on a night when everybody is calling.
The two pricing questions, written down
Call-out fee, and whether it applies to the repair. After-hours labor rate against the standard rate. Ask both before agreeing to the visit. Afterwards you have no leverage and no alternative.
Do not attempt anything involving refrigerant, gas or the burner compartment
Federal law requires Section 608 certification to open a refrigerant circuit or to purchase refrigerant, and that has covered R-410A since 2018. Combustion equipment is a safety system. Nothing in the checks above touches either, and that is deliberate rather than cautious.
Do not agree to a replacement over the phone at night
A replacement is a fifteen-to-twenty-year decision. There is no version of it that has to be made before morning, and any pressure suggesting otherwise is about the sale rather than about your house.
Real blind spots
What else can this triage not do?
The triage is not a medical assessment and it is not a substitute for calling emergency services. Confusion, headache, nausea, dizziness or breathlessness in a building with a fuel-burning appliance are symptoms to act on immediately, from outside the building. This page sorts appliances; it does not assess people.
It cannot diagnose the fault: Two systems presenting identical symptoms routinely have entirely different causes, and the diagnosis requires instruments on the equipment. What this page does is decide how fast somebody with those instruments needs to arrive.
It does not know your climate or your building: A 95°F afternoon is routine in Phoenix and a public health event in a city where most housing has no cooling at all.
A freezing night is unremarkable in Minnesota and a burst-pipe event in a house with pipes in an uninsulated exterior wall. The thresholds on this page are general and your local emergency-management guidance is specific.
It cannot tell you what the visit will cost: HyreHVAC does not install, service or sell HVAC equipment, and holds no data on quotes, invoices or finished jobs. Nothing here is a price we observed.
That is also why these tools can tell you to keep the system you have. We can tell you which two questions to ask before the van is dispatched, which is more actionable than a national average would be even if we had one.
It cannot dispatch anybody: HyreHVAC is not an emergency service, does not operate a call center, and does not send technicians. There is no version of this page where the answer is "click here and we will send somebody", and that is why it can tell you the answer is to wait until Monday.
It cannot see whether the system has been maintained: A history of recorded service readings changes what a symptom means. The same noise tells a technician more on a system with records. If you have those records, give them to whoever attends. If you do not, our maintenance calendar covers how to start keeping them.
Questions this calculator answers
What do I do if I smell gas near my furnace?
Leave the house and call your gas utility or 911 from outside. Do not use light switches, the thermostat or a phone inside, because a spark can ignite gas. Do not go back in until you are told it is safe.
What should I do if the carbon monoxide alarm goes off?
Get everyone outside into fresh air, then call 911 from outside. Do not open windows first or look for the source. Carbon monoxide has no color or smell, so the alarm is your only warning.
Is no AC in summer an emergency?
Usually not, unless someone at home is at risk of heat illness, such as an infant, an older adult, or a person on certain medications. Check the thermostat, filter and breaker first. After-hours calls cost more, so ask the rate.
Is no heat an emergency?
Yes, when it is freezing outside and pipes can freeze, or someone vulnerable is at home. Otherwise it is urgent but can often wait for regular hours. Never heat a room with an oven, gas range or outdoor heater.
My outdoor unit is iced over. Is that an emergency?
No, but it is urgent for the machine. Switch the system to fan-only or off. Running it iced can destroy the compressor and turn a cheap airflow fix into a replacement.
Sources and methodology
Figures dated August 23, 2026. Last reviewed .
Residential Energy Consumption Survey 2020, public use microdata (US Energy Information Administration, retrieved 2026-09-04. Source of the equipment-age distribution and the cooling-access figures. Standard errors from the 60 replicate weights supplied with the file.)
Residential HVAC Installation Practices: A Review of Research Findings (US Department of Energy, Building Technologies Office, retrieved 2026-09-04. A systematic review of 44 field-study reports. Source of every fault-prevalence range and of the tune-up and combined-repair savings figures.)
Section 608 technician certification requirements (US Environmental Protection Agency, retrieved 2026-09-04. 40 CFR Part 82, Subpart F. Certification types and the refrigerant sales restriction, which has covered HFC substitutes since January 1, 2018.)
Carbon monoxide poisoning (CDC, retrieved 2026-08-23. Leave and get fresh air; emergency services. Not an HVAC booking.)
Natural gas safety (Pipeline and Hazardous Materials Safety Administration, retrieved 2026-08-23)
Related
Repair vs replaceAfter it is safe, the money question is still remaining life.