Updated: 5/13/2024

During the long, humid summers in Downers Grove, it’s unlikely that your gas furnace comes to mind very often. While you’re busy enjoying vacations and popsicles, though, your gas furnace still uses energy, albeit a lot less energy than it does in the winter. Since you don’t need your furnace during the summer, the obvious question is whether or not you can turn off your furnace completely until it’s cold enough to need it again. To better understand the pros and cons of this action, check out this deep dive into furnaces from Fire 'n' Ice Heating & Cooling, Inc..

How a Furnace Works

A gas furnace uses a burner to burn either natural gas or propane. When the furnace is running, this flame heats a heat exchanger which then heats the air that passes by. However, the burner can’t start burning without an initial flame. That initial flame comes from the pilot light. Once the pilot light has started the process, the blower fan blows cool air over the heat exchanger until your thermostat detects that the room has reached the desired temperature. At that point, the furnace shuts down all of its components, except for the pilot light, which burns all the time.

Understanding Your Furnace Type

Your furnace is one of either of two types; water-based or a forced-air heating system. Whichever type you have, the system will have a flue pipe and a thermostat. The only difference between these two systems is in how they deliver heat to your house.
The water-based systems transport heat to your home as water or steam through a radiator, radiant floor heating, or a baseboard heater. These systems need a boiler. You may hear them being referred to as hydronic systems.

Forced-air heating systems disperse heat in the form of warm air. The heat disperses through floor and wall vents. This system needs a furnace, and it is the most common system for homes.

Should You Turn Off Your Furnace in the Summer?

Your furnace doesn’t go off even during the hot summer months. You need to understand how the two systems work so that you can know why they stay on.
The thermostat in a water-based system detects when the temperature goes below the set level. When that happens, the gas burner is engaged, and it starts drawing gas. The fuel ignites inside the combustion chamber. When the gas lights, the boiler starts heating the water.

This hot water circulates through the baseboard heaters or the radiators. Any emissions go through the flue pipe and the chimney. Once the water cools, it goes back to the boiler and is reheated.

The steam system works almost the same way. However, instead of circulating water through the radiator, the system boils water until it produces steam. The steam goes through pipes that connect to the radiator and heats the home.

Forced air heating systems work the same as hot water systems in the first four steps. They draw gas that ignites in the combustion chamber. The system then draws cold air from your home and heats it. Inside the burner, there is a blower fan that fans the heated air through feed ducts. The feed ducts then direct the heated air into floor and wall vents.

Just like in the water-based heating system, the emissions from the furnace go out through the flue pipe and chimney.

Because the thermostat of the system is turned all the way down, you would think that the system will not work at all. But that is not the case. The system still burns fuel.

Why Does Your Furnace Burn Fuel Even When the Thermostat is Turned All the Way Down?

The pilot light in older furnaces, 15 years or older, burns fuel all the time. These older systems have a pilot light that doesn’t go off. If the tiny blue light ever goes off, your furnace will not light at all. The idea behind the pilot light was to ignite the furnace automatically without you having to light it manually.

Although the pilot light was a brilliant idea, it makes the system less efficient. Its inefficiency goes beyond the fact that the pilot light doesn’t go off at any time. It affects the AFUE (Annual Fuel Utilization Efficiency) rating. AFUE rating shows the percentage of the gas used to generate heat from the total amount of oil the furnace burns.

These older systems have an AFUE rating of between 56% and 70%. Newer systems with an electronic starter have an AFUE rating of between 80% and 98.5%.

The electronic ignition is instant and doesn’t need to stay on at all times. Further, newer systems have other features, such as a sealed combustion chamber that reduces the amount of fuel they burn.

Turning Off Your Furnace in the Summer

It’s a good idea to turn off your furnace during hot months. If left on, it will continue to consume energy. The furnace contains some electrical components like sensors that can needlessly draw power throughout the summer. If your furnace has a pilot light, it will use up unnecessary gas during summer when left on.
You might think you have switched off your unit by turning the thermostat settings to cool the house. While this stops the furnace from working, it won’t shut it down. You should ensure that you cut off the gas line and the electric supply to avoid wasting energy.

If you live in areas that experience warm temperatures all day and night, consider turning off the furnace during summer. And, if you don’t live in the house full time, it would be best to turn off the furnace during summer to save energy.

By switching off your furnace in the summer, you will save on energy and pay lower utility bills every month. However, if you link your system to your AC, you need to keep the furnace on. If you use it to heat water, you may also not turn it down unless you buy a standalone boiler.


Turning off your furnace during the summer can help you save on energy costs and reduce unnecessary wear and tear on your HVAC system. However, it’s essential to consider your specific circumstances and the type of furnace you have before making a decision. If you’re unsure, it’s always a good idea to consult with a professional HVAC technician to ensure you’re making the right choice for your home.

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