February 2, 2022

Now that we’re in the heart of winter, you’ve probably been using your furnace to stay comfortable. Modern furnaces are more efficient than ever, using the shortest possible heating cycle to reach your preferred temperature. But how do you know if your furnace’s current cycles are efficient enough? How often should you run your furnace in cold weather?

These heating cycles have a big impact on your monthly energy bill, so determining the ideal schedule can help your HVAC system run more efficiently. Your average furnace will run several times every hour, sometimes as low as 3-4 cycles or as high as 9. Ultimately it depends on:

  • the size of your home
  • the size and power of your furnace
  • the outdoor temperature
  • and your current thermostat settings

But this is if everything is working like it’s supposed to. How do you know if your furnace is running too frequently? Check out these tips below.

Furnace Heating Cycles Average 10 to 20 Minutes

To complete a furnace heating cycle, the thermostat first directs the furnace to start. Once the heat is flowing, it will continue to run until the thermostat detects the set temperature. For your typical residential furnace, that cycle lasts around 10-15 minutes. Sometimes a cycle can last up to 20 minutes, usually in particularly cold weather.

There are lots of things that can influence the length of your furnace’s heating cycle. Where the thermostat is located, whether the furnace is correctly sized for your home etc. For most homes, these factors won’t make much of a difference. If your heating cycle is consistently over 20 minutes, however, it could be a sign something is wrong. In fact, both excessively long and short heating cycles could be a sign of trouble.

5 Reasons Your Furnace Is Running Too Long

  1. Severe cold: The most straightforward reason your furnace is running a long time is extremely cold weather. Out on the high plains, we’re more than familiar with brutal winter temperatures.
  2. A malfunctioning thermostat: Since the thermostat is responsible for turning your furnace on and off, a malfunction could lead to extended heating cycles or even running constantly.
  3. Inadequate home insulation: While almost every home has some form of insulation, it’s often not enough for true energy efficiency. Most heat loss is through poorly sealed or insulated ductwork. The more heat is lost, the more your furnace has to work to make up the difference.
  4. The furnace is too small for your home: HVAC systems should be appropriately sized, meaning the model you choose provides an efficient heat output. If your furnace was sized too small, it will be working overtime as it tries to reach the set temperature.
  5. Malfunctioning components: When key components like the blower motor or limit switch malfunction, your furnace may experience longer cycles or even run constantly. Running constantly can overheat your furnace, and if the limit switch is damaged, it may not be able to safely shut down.

Even if the furnace is running normally, long furnace cycles can lead to higher energy bills. But what about heating cycles that are too short? Wouldn’t a short heating cycle mean your furnace is just running extra efficiently? Not necessarily. It could actually be short cycling.

Short-Cycling Furnaces Start and Stop Repeatedly

When a furnace is short cycling, its heating cycles may not be long enough to maintain comfortable temperatures indoors. So not only can this disrupt your sense of comfort, but it increases the strain on components involved in starting and stopping your furnace. This can cause your energy bill to spike and may even shorten the life span of your HVAC system.

Here are a few of the most common reasons furnaces experience short cycling:

  1. Old age: As your furnace gets older, it generally starts to run less efficiently. Particularly older models may begin to short cycle simply because it’s no longer powerful enough to provide adequate heat.
  2. Obstructed airflow: Dirty air filters or a clog in the ductwork can reduce the air coming into your furnace. This can lead to the furnace overheating, which is the most common source of short cycling. Keep up with cleaning or replacing your air filter to ensure steady airflow!
  3. Damaged or dirty flame sensor: If the flame sensor isn’t working correctly, it may not be able to consistently recognize that the flame is active. This inconsistency appears as short cycling.
  4. The thermostat is too close: Your home’s thermostat should be placed in a part of your home that ensures an even distribution of heat. If it’s too close to the furnace, it may shut off before the rest of your home receives enough heat.

To ensure your furnace is providing consistent, energy-efficient heating, keep an eye on how long its average heating cycles are. If something seems wrong, don’t hesitate to call a trusted local service company like AC Mechanical.

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