Should a Furnace Switch Be ON or OFF?

This is a question many people ask, especially at the end of the heating season, typically winter in most regions – should you turn off the furnace now that you’re don heating? Or do you leave it on?

It’s an even bigger concern given that leaving the switch on the entire year, even when you don’t need heating, may seem unsafe. Also, what about the pilot light, assuming you have a standing pilot system? Wouldn’t you lose a lot of fuel unnecessarily in the process?

We answer these and many other “should a furnace be switched ON or OFF” questions below, so you know what’s best.

What is a Furnace Power Switch?

Let’s begin by attempting to demystify the furnace power switch. More accurately known as the furnace disconnect or furnace disconnect switch, the furnace’s power switch is an ON/OFF switch that completes or disconnects the furnace’s circuitry to keep the unit on or turn it off. 

In most cases, the switch is mounted on the side of the furnace or a nearby wall. It’s easily visible and accessible as most building codes require that the switch be “within sight.” So, you shouldn’t struggle to find it. 

Types of Disconnect Switches 

Furnace disconnect switches come in two main varieties. The most common one is a single-pole switch similar to lighting system switches. It also works the same way as a standard light switch. As such, the switch must be rated for the amperage and voltage of the furnace’s circuit.

However, you may find a slightly different type of switch in older furnaces, characterized by a fuse and toggle switch. This means that you can switch off the furnace in two ways. First, you can toggle the switch to turn off the furnace. Alternatively, you can unscrew the fuse to turn off the furnace. 

Unfortunately, it’s not up to you to choose the type of switch you want for your furnace, as most furnaces arrive with a disconnect switch. Indeed, many manufacturers specify the type of switch to use on their furnaces. Additionally, your local codes may require fused switches. So, it’s best to check with the local building authority first.  

Notably, some local authorities demand lockable breakers instead of standard switches. As the name suggests, a “lockable breaker” is a circuit breaker switch that you can lock to prevent unwanted or accidental tampering, such as reset and turn-ons. 

Most lockable circuit breakers come with a lock system and a cylinder lock so you can manually lock the breaker switch. You’ll also get a key to unlock the switch in the tripped position. However, you cannot lock the breaker in the ON position.  

Where is the Power Switch on a Furnace?

The furnace switch is found either on the furnace itself or the wall nearby. It looks like a standard electrical power switch such as the light switches in your room and is typically unlabeled.

Remember that it should be easily visible. The main reason for this is that building codes state that the electrician or HVAC technician must keep track of the switch’s position (ON or OFF) throughout during maintenance or repairs. So, if you’re struggling to locate it, even to the extent of moving a few objects, it might be better to refer to your owner’s manual for directions. 

Should Furnace Switch be ON or OFF?

A common question homeowners ask is whether you should leave the furnace switch ON 24/7 365 or switch it OFF during the summer when you don’t need heating. The short answer is – keep it ON. There are several instances when it’s better to turn off the furnace switch, as we’ll see shortly.

However, if you own a modern furnace and the appliance is installed correctly, it’s a lot more convenient to keep the disconnect switch ON.

Reasons to Keep the Furnace Switch ON

The main reason is that leaving the furnace running means you no longer have to worry about turning it ON and then OFF again. You may not even need t check the furnace with good maintenance. Instead, the furnace will automatically spring to action as soon as the cold weather sets in and go quiet when it becomes warmer indoors. 

Additionally,

  • Modern furnaces don’t use up energy in the OFF cycle

Many homeowners feel the need to turn off the furnace in the summer to save energy that would otherwise go to waste due to the standing pilot light. According to the Department of Energy, the standing pilot can consume up to $219/year. You’ll be glad that modern furnaces don’t have a standing pilot.

Instead, modern units are equipped with intermittent or hot-surface pilot systems that stay off until it’s time to light the burners. So, you don’t have to worry about standing pilot costs.

  • No more safety risks associated with standing pilots

Many homeowners also prefer to shut down standing pilot furnaces during the summer to ensure safety. The standing pilot poses a significant danger, especially in the summer when no one checks on the furnace. It can accidentally cause a preventable fire. 

As such, the absence of the pilot light in the modern furnace significantly improves safety. You no longer have to worry about checking the pilot flame. This also means you can live more peacefully even with the furnace ON. 

  • You can use the furnace for fanning 

Finally, it often escapes many people that you can rely on the furnace to fan your home during the summer. Typically, a condensing furnace (high-efficiency models) requires 150 CFM for every 10,000 BTUs. It means that the average condensing furnace comes with a built-in fan rated between 1,200 CFM and 1,800 CFM, with some as powerful as 3,000 CFM. This is as good as most standalone residential fans. 

You may not rely on the built-in furnace fan alone during the summer. However, it can plug cooling gaps in your HVAC system, so you don’t need a massive air conditioner or too many standalone fans. Suppose you’re worried about someone accidentally tampering with the switch. In that case, many manufacturers and third parties now have child-safety switch protective covers and toggle guards to lock the switch out of the reach of kids. 

How Do I Know if my Furnace is ON?

The easiest way to determine whether your furnace is turned ON and getting power is to check with the thermostat. Modern thermostats have a switch that says ON or AUTO. The ON switch keeps the fan running as long as the furnace is switched ON and getting power, while the AUTO mode only engages the fan if the furnace is ON and producing heat. 

So, all you need to do to test whether your furnace is ON is select the ON setting on the thermostat. Make sure you have power. Then head to the thermostat and toggle it from AUTO to ON. If the furnace fan starts blowing, the furnace is switched ON. 

When Should you Turn your Furnace OFF?

Although the furnace switch should be ON all the time, you’re entirely at liberty to switch it OFF depending on the circumstances. The following are just a few situations when turning it off may make the most sense;

  • You have a standing pilot furnace

Unfortunately, traditional, standing pilot furnaces are unsafe and costly to keep ON when you don’t need heating. The constantly burning pilot flame presents a significant fire and burn risk, especially if you have young children. Additionally, no one wants to lose $220 per year. Therefore, switching off the furnace in the summer is more sensible. 

  • During repair and maintenance

Never work on the furnace with the disconnect switch ON. It exposes you to a severe risk of electrocution. Moreover, working on the furnace while it’s ON increases the risk of accidental short-circuiting, which may result in irreversible internal damages, necessitating expensive replacements. So this is another instance when switching off the appliance makes sense. 

How to Turn OFF a Furnace – Step-by-Step

Turning off the furnace is a straightforward process. However, it’s not just about toggling the ON/OFF switch and calling it a day. Instead, proceed as follows;

  1. Turn off the pilot light by switching the knob to the off position
  2. Shut off the main gas supply at the main gas valve
  3. Now, toggle off the disconnect switch.  

What Happens if I Turn the Furnace OFF?

However, as you turn off the furnace, remember that it’s not entirely the best thing to do. The following are a few complications that may result from turning your furnace off, especially when it’s still cold out there;

  • Rusting: Furnaces produce hot exhaust fumes that contain significant quantities of moisture. Shutting the appliance down before the moisture is vented completely can cause moisture buildup, resulting in rusting. 
  • Frozen pipes: Keeping your home warm during the cold weather isn’t just crucial for your wellbeing but also for the structural integrity of the home and plumbing system. If it gets a little too cold and the furnace is off, you run the risk of frozen pipes and potential water damage. Water damages can be very costly. 
  • The buildup of dust and debris: Finally, a dormant furnace also attracts the buildup of dirt and debris that can easily cause malfunction. 

FAQs

Is it safe to turn the furnace switch OFF? Yes, it’s completely safe to turn the furnace switch OFF as long as you also turn it OFF at the circuit breaker. 

How do I turn my furnace back on – step by step? It’s the same process as turning it off. First, turn ON the pilot system by toggling the knob ON, turn on the gas supply at the main valve, and then switch ON the disconnector switch on your furnace. 

What do I do if I accidentally turn off the furnace switch? Don’t panic. You can easily turn the furnace back on by flipping the same switch. 

Why do I have to turn my furnace off and on? Turning the furnace OFF and then back ON resets the appliance. This can resolve internal issues such as a temporarily stuck draft inducer switch. 

How often should my furnace turn on and off? Typically, furnaces run for 15 minutes, then cycle off for 15 minutes before cycling back ON. So, your furnace should cycle on and off about four times every hour. 

Summary 

Now you know everything about the furnace’s ON’OFF switch, better known as the disconnect switch. Remember that the switch can become problematic occasionally, even refusing to toggle ON or OFF. Make sure to call an HVAC professional immediately that happens. More importantly, don’t forget to schedule seasonal tune-ups to keep your disconnect switch and the furnace, in general, in the best working condition.  

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