The Nonstop Furnace: Why It Runs for So Long

A common problem homeowners may face with their furnace is when the furnace keeps shutting off early, failing to complete a full heating cycle. 

But the opposite problem can occur as well: a furnace that runs for too long, seeming to never cycle down. This creates a huge energy waste, makes a house to hot, and puts so much strain on the furnace that it will wear down rapidly. If you’ve encountered a “runaway furnace,” you’re right to feel concerned. In most situations, a furnace that’s running for too long will need professional furnace repair in Maumelle, AR.

We’ll look closer into this problem and the reasons it occurs.

Why Does a Furnace Run Constantly?

• Dirty air filters restricting airflow through the system
• Thermostat issues causing incorrect temperature readings
• Leaky ductwork allowing heated air to escape
• An aging furnace struggling to heat the home efficiently
• Poor insulation causing heat loss throughout the house
• A furnace that is undersized for the home’s heating needs

A furnace that runs nonstop often signals reduced efficiency or a system problem that may require professional heating and air conditioning repair to prevent higher energy costs and unnecessary wear.

How long should a furnace run normally?

There’s no set time for a furnace’s heating cycle; it will vary depending on how cold the house is and how the thermostat is set. The average running time under standard winter conditions is around 15 minutes. In colder weather, the furnace may run through cycles more often, but it shouldn’t run much over 20 minutes. If it does—and your home is getting noticeably warmer than usual—you may need to call for expert furnace troubleshooting and repair.

What can cause this longer running time?

We’ll list the most common culprits for a furnace that’s running too often:

• Thermostat trouble: The thermostat controls when the furnace and blower fan turn on and off, so if the thermostat malfunctions, it can throw off the furnace’s normal cycling. This can be due to the thermostat sensing incorrect indoor temperatures, or losing its connection to the furnace.
• Clogged furnace filter: This is a common source of the trouble, and thankfully one you can fix on your own. A clogged filter lowers the blower’s ability to draw sufficient air into the furnace to heat it, and this can lead to the furnace running for too long. Please change the filter every 1 to 3 months to prevent this from happening.
• Heat exchanger problems: The heat exchanger is the metal part in the furnace that transfers heat from combustion gases to the air moving into the ventilation system. Heat exchanger problems can cause the furnace struggle to provide enough heat. Heat exchanger issues are potentially hazardous and need professional attention right away. 
• Wrong sized furnace: If you have a relatively new furnace, the problem may be that whoever installed it did not properly size it for the house. An undersized furnace will have to run much longer to heat a house. The only repair for this problem is to upgrade to a properly sized furnace with one that’s accurately sized. This is one reason to always go to experienced professionals for a new furnace installation. 

Frequently Asked Questions

Question: Why does my furnace keep running for so long?
Answer: A furnace may run too long because of thermostat problems, a clogged filter, heat exchanger issues, or incorrect system sizing. If the furnace runs well past a normal cycle and your home feels too warm, it may need professional attention before the extra strain causes more damage.

Question: How long should a furnace run during a heating cycle?
Answer: Furnace run times vary based on outdoor temperatures, thermostat settings, and how cold the home is. Under standard winter conditions, a typical cycle may last around 15 minutes. If it regularly runs longer than 20 minutes and the house keeps getting warmer, something may be wrong.

Question: Can a dirty furnace filter make the furnace run nonstop?
Answer: Yes, a clogged furnace filter can restrict airflow and make it harder for the blower to move air through the system. When the furnace cannot heat and circulate air properly, it may run longer than normal. Replacing the filter every 1 to 3 months can help prevent this issue.

Question: Is a furnace that runs constantly dangerous?
Answer: It can be, especially if the problem involves the heat exchanger or another internal component. Heat exchanger problems may create safety concerns and should not be ignored. If changing the filter and checking thermostat settings do not solve the issue, shut the furnace down and call a professional.

Question: Can the wrong furnace size cause long heating cycles?
Answer: Yes, an undersized furnace may have to run much longer because it struggles to heat the home properly. This is more likely with a newer system that was not sized correctly during installation. In that case, the lasting solution may be replacing it with a properly sized furnace.

Call us for furnace help

If the furnace problem isn’t a simple case of a clogged filter or the wrong settings on the thermostat, we recommend you shut down the furnace and call our technicians. You don’t want to place any extra strain on the furnace, and you want to make sure there isn’t a safety concern. We’ll be out to get your furnace heating again. We won’t do the job unless we do it right, no matter how hard it is!

Dewees HVAC proudly serves the Conway area—we’re here to keep you comfortable! Schedule help for your home’s furnace with our team.