Quick answer
An HVAC emergency is anything that threatens safety, health, or your home: no heat in winter, any gas smell, suspected carbon monoxide, a major water leak from your system, or no cooling during a heat warning when vulnerable people are home. These need a 24/7 call. Weak airflow, one cold room, or noisy equipment that still runs can usually wait until morning across the GTA and Ontario.
What counts as an HVAC emergency is anything that can hurt someone or damage the house before the next business day: a gas smell, suspected carbon monoxide, no heat in freezing weather, water spreading from the equipment, or no cooling during a heat warning with a vulnerable person at home. Everything else is urgent at most. The test is three questions, and you can run it at 2 a.m. with no technical knowledge.
The three-question test
- Is anyone at risk right now? A gas smell, a sounding CO alarm, or a household member who is dizzy, nauseous or confused means leave the house and call 911 — not a contractor.
- Will the house be damaged by morning? Below freezing with no heat, water pooling near the furnace, or a tank leaking above a finished basement all say yes.
- Is the equipment doing something it should never do? Repeated breaker trips, a burning-plastic smell, sparking, or a furnace that keeps lighting and dropping out are shut-it-off-and-call signals.
One yes means call the 24/7 line now. Three no's means book the first regular slot and go back to bed — you lose nothing but a cool evening.
Call right away — these are true emergencies
- Any gas smell (rotten-egg odour): this comes first. Don't touch switches or phones indoors — leave the building, then from outside call Enbridge Gas at 1-866-763-5427 or 9-1-1. See what to do if you smell gas.
- Suspected carbon monoxide — a CO alarm sounding, or flu-like headache/nausea/dizziness that eases when you leave the house: get everyone, including pets, to fresh air and call 9-1-1. More on furnace CO risk.
- No heat in winter, especially below freezing: supply lines in outside walls and the rim joist can freeze the same night, and waiting doesn't make the repair smaller.
- A major water leak from the furnace, AC, or water heater that's pooling or spreading toward electrical or finished space.
- No cooling during a heat warning when infants, seniors, or people with medical conditions are in the home — heat illness is a real risk.
- Repeated breaker trips or any burning/electrical smell from the equipment — shut it off and call.
Cooling and hot-water emergencies
Heat is the emergency people underrate. During an Environment Canada heat warning, a top-floor bedroom in a 1970s 2-storey or a west-facing condo can hold above 30°C all night, which is dangerous for infants, anyone over 65, and anyone with a heart or lung condition — what to do if the AC fails in a heat wave covers the house and the people before the equipment. Water heaters run the other way: no hot water is an inconvenience, but a tank leaking from the seam, or any gas smell at the water heater, is a same-night call.
Usually safe to wait until morning
- Weak or reduced airflow while the system still produces some heat or cool air
- One room that's colder or warmer than the rest of the house
- Equipment that's noisier than usual but still running normally
- AC out on a mild day with no heat warning and no vulnerable occupants
- No hot water — uncomfortable, but rarely damaging to wait 12 hours
The grey areas
Some calls fall in between. A small drip from the AC during cooling season can often wait a day, but a furnace leaking water in heating season shouldn't — on a high-efficiency unit it often means a blocked condensate trap that will lock the furnace out. Banging on startup or a grinding blower warrants prompt attention even if the unit still runs. When in doubt, call the 24/7 line and describe what you're seeing — a good dispatcher will tell you honestly whether it can wait.
Emergency questions we answer on the phone
- Is a furnace blowing cold air an emergency? If the blower runs, power and control are intact and the house cools slowly — urgent on a January night, bookable for morning in March.
- My furnace short-cycles — call tonight? If it still heats between cycles, morning is fine. If it locks out and stays off in freezing weather, call now.
- The CO alarm chirps once a minute — emergency? A single regular chirp is a low battery or an expired sensor; replace it today. Four fast beeps repeating is an alarm: get everyone out and call 911 from outside.
- Power is out and the furnace is off — is that an HVAC call? No — a furnace cannot run without electricity. Report the outage to your utility, and see the frozen-pipe steps if it stretches past a day.
- Does using the emergency line cost more? Not at ZK. Many companies do add an after-hours fee, so ask before authorizing a visit.
ZK Mechanical answers day and night with no overtime surcharges, and we'll give you a straight answer about urgency before dispatching. If it's a real emergency, call (647) 801-1252 for 24/7 emergency HVAC service; if it can wait, contact us to book a same-day or next-day visit across the GTA and Hamilton.