How to turn off a furnace: thermostat first, then the switch
Turning a furnace off takes about a minute. The order matters, and so does knowing when to leave it running or leave the house.
The safe way to turn off a furnace is at the thermostat first
Set the thermostat to Off, or lower the setpoint below room temperature. That stops the call for heat and the furnace finishes its cycle on its own. It is the right first move for almost every reason you would want the furnace quiet.
Need it fully powered down, say for a long trip or before a technician arrives? Use the furnace's own switch. It takes about a minute.
How to cut power at the furnace
- Set the thermostat to Off and wait for the blower to stop.
- Find the service switch. It looks like a light switch on or beside the furnace, or on a nearby wall or joist.
- Flip it to Off.
- Leave the furnace door and panels closed.
No switch? The breaker marked for the furnace does the same job. Label it so nobody flips it back on by accident.
Which method fits which situation
| Situation | What to use | Why |
|---|---|---|
| Warm weekend, heat not needed | Thermostat Off | Simple and instantly reversible |
| Away for weeks in winter | Lower setpoint, not full off | Keeps pipes from freezing |
| Technician coming, or odd noises | Thermostat Off, then service switch | Removes power from the blower and controls |
| Smell of gas or a CO alarm | Leave the house | Do not stop to switch anything off |
Do not turn off the furnace in a freeze
If you are leaving for a cold stretch, do not shut everything down. Set the thermostat to a low but safe temperature instead. A house that drops below freezing can burst pipes, and that costs far more than a few days of low heat.
The gas valve is not part of a routine shutoff
You will see advice online to close the gas valve. For a normal off, you do not need to. The thermostat and service switch are enough. Leave the gas line alone unless your gas utility or a licensed HVAC technician tells you to touch it.
One rule beats everything above. If you smell gas, or a carbon monoxide detector sounds, do not stop to switch anything off. Leave the house at once and call your gas utility or 911 from outside.
When off does not mean off
Furnace still running after you set it to Off? Check that the thermostat is actually set to Off and not just to a low target. If it keeps running, cut power at the service switch and call a technician. Do not open the cabinet to find out why.
Frequently asked questions
What is the safest way to turn off a furnace?
Set the thermostat to Off, wait for the blower to stop, then flip the furnace's service switch. If there is no switch, use the labeled breaker.
Should I turn off the gas valve to the furnace?
Not for a routine shutoff. The thermostat and power switch are enough. Touch the gas valve only if your gas utility or a licensed HVAC technician tells you to.
Can I turn the furnace off completely when I travel in winter?
It is risky. Pipes can freeze if the house gets too cold. Set a low but safe temperature on the thermostat instead of shutting the system down.
What if I smell gas when I try to turn the furnace off?
Do not switch anything. Leave the house immediately and call your gas utility or 911 from outside.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- ENERGY STAR. Furnaces
- CDC. Carbon Monoxide Poisoning Basics