Skip to Content

Why Is There an Outlet on My Furnace?

The National Electric Code by the National Fire Protection Agency (NFPA) requires residential and commercial establishments to allot a dedicated circuit for HVAC systems such as furnaces. So, why is it that most furnace systems in the country have a receptacle next to them? Doesn’t this go against the said National Electric Code?

There is an outlet on your furnace because it can be used to power circulator pumps, dehumidifiers, condensate pumps, and humidifiers. However, note that the NEC states that these outlets can only accommodate devices vital to HVAC system operation. The furnace still needs its own dedicated circuit.

Keep reading for a more detailed explanation on what appliances you can run on the receptacle located near your furnace according to the National Electric Code. We’ll also be discussing how DIYers can safely remodel HVAC and furnace wiring without going against building codes and regulations.

Devices That You Can Plug Into the Outlet Located on the Side of Your Furnace


Dry air does not only feel “colder,” but it also puts one at risk of various complications such as sore throat, asthma, dry skin, and nasal irritation, among others. A simple, efficient way to resolve this is to attach an in-duct humidifier to the furnace. You can plug the humidifier into the outlet located on the side of the unit as it is considered an integral part of the HVAC system. 

Increasing air moisture during the colder seasons also reduces the heating load on your circuit. Furnaces won’t need to exhaust as much energy to heat up areas that are properly humidified because these feel warmer than dry, dehumidified air.

A good option we would recommend is Aprilaire’s Whole-Home Furnace Humidifier. It’s a high-quality manual, single sensor device capable of humidifying large spaces up to 3,000 square feet (914 square meters) in size.

Aprilaire – 500MZ 500M Whole Home Humidifier, Manual Compact Furnace Humidifier, Large Capacity Whole House Humidifier for Homes up to 3,000 Sq. Ft.

Electrostatic Air Cleaners

Another device you can connect to your furnace is an electrostatic air cleaner. As the name suggests, this device rids the air of dust, allergens, and fine particles through electrostatic technology. Again, this is considered a part of your HVAC system, so it can run on the same circuit as your furnace.

Having an electrostatic air cleaner running simultaneously with your furnace allows you to clear the air of harmful contaminants. Not only is clean air more beneficial for the human body, but it’s also less damaging and risky for your HVAC system. Dust buildups can lead to some serious long-term issues.

Condensate Pumps

Furnaces — especially ones equipped with a humidifier — condensate water while they are operating. Condensation is generally harmless. The excess water only becomes an issue when they pool up and flow to sidings, walls, flooring, and other appliances/fixtures. 

A quick, efficient way to resolve this issue is to install a condensate pump. This device pumps out excess water from your heating or cooling system, sucks them into a drain line, then redirects the condensate to the designated drainage. Condensate pumps can run simultaneously with your HVAC.

Check out this Raybend AC Condensate Pump. It’s a heavy-duty device equipped with a 1/20 HP motor and has a maximum hourly flow rate capacity of up to 173 gallons (655 liters).

Raybend AC Condensate Pump – for Air Conditioner Units, Furnaces, and Dehumidifiers

Circulator Pumps

If you plan on placing all your HVAC systems in the same unfinished space, we recommend installing the circulator pump near the furnace as well. This device is essentially in charge of circulating different types of liquids and gasses found in your HVAC system’s circuits and pipelines. They’re essential when operating both your heating and cooling system.


As we mentioned, humid air feels warmer. Extra humidity during the cold winter months might feel great, but trust me, excess moisture in the air will make the hot summer days unbearable. 

To combat this, you can install a whole-home dehumidifier. Since this is another integral part of your HVAC system, it can run on the same circuit as your furnace.

Cooling Coils

To make air conditioning installation easier, opt to attach a cooling coil to the outlet on your furnace. This is ideal for those who want to equip their home or business space with a central air conditioning system. 

Note that you might have to follow different regulations if you plan on installing a mini-split air conditioning system. Also, mini-split air conditioners don’t belong in unfinished spaces. These appliances are often used to cool finished spaces such as living rooms, bedrooms, and kitchens.

Other National Electric Code Guidelines That You Need to Remember Regarding the Outlet on Your Furnace

Differentiating between devices you can and cannot plug into the outlet on your furnace is great, but this isn’t all you need to know. DIYers who frequently tinker with their HVAC systems would do well to understand the other National Electric Code guidelines set by the NFPA. These include:

The Furnace Disconnect Switch

If you’re exploring your furnace for the first time, you might notice a service switch located right beside the outlet. This is called the furnace disconnect switch. 

As the name suggests, it’s a switch that allows users to turn their furnaces on and off with just the push or flick of a button. Having one eliminates the need to run to the breaker in case of an emergency. 

The National Electric Code requires the furnace disconnect switch to be positioned beside the unit itself. Generally, it should be within arm’s reach.

Learn more about the furnace combination switch in this helpful guide video by grayfurnaceman:

The Use of the Outlet as a Service Receptacle

You cannot use the outlet near your furnace as a service receptacle. As we mentioned earlier, the National Electric Code requires residential and commercial establishments to have a dedicated circuit for their HVAC system — this includes the furnace. 

Remember, you can only plug devices that are necessary for daily HVAC system operation. This does not include any lamps or tools you or your contractor might need while working on the furnace system. You’ll have to use a separate outlet or receptacle that’s connected to an entirely different circuit. Otherwise, you’ll still run the risk of overloading the furnace’s circuit line.

Also, we mentioned that the furnace disconnect switch is connected to the outlet on the side of your furnace. If you need to make adjustments to the system, you’ll have to turn the switch off, so either way, the outlet won’t have the power to function as a service receptacle even if you wanted to.

The Use of Unfinished Spaces

Apart from dedicating a unique circuit for your furnace and keeping the outlet open for HVAC devices, you also need to maintain the area wherein your heating and cooling system is placed. 

Central HVAC units such as furnaces are often stored in unfinished spaces. These are defined as areas in an establishment that do not have floor coverings, ceiling/wall finishing, or respective toilets and sinks. They are uninhabitable and must only be used for work, service, and storage purposes.

Generally, the National Electric Code permits the use of unfinished spaces for HVAC system storage. You can even heat and cool these rooms. Provided, of course, that they meet the criteria to be qualified as an unfinished space.

Final Thoughts

Overall, you can plug devices such as humidifiers, dehumidifiers, cooling coils, and condensate pumps in the outlet located on the side of your furnace. 

However, you still have to abide by the National Electric Code regulation that states furnaces — as with any other HVAC system — require their own circuit, so you can’t use the same line to power devices unrelated to daily HVAC operations.

Also, be careful when rewiring your HVAC circuit. Make sure to turn the disconnection switch off, so the outlet doesn’t generate any electricity while you’re working on the system.


  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

As an Amazon Associate, we earn from qualifying purchases. We may also earn commissions if you purchase products from other retailers after clicking on a link from our site.