Furnace Short Cycling When Cold

The winter weather puts a long of strain on heating appliances. After months of dormancy, the furnace suddenly finds itself running round the clock – sometimes at full speed.

As such, it’s it isn’t uncommon to experience finance short-cycling during the peak of winter. Fortunately, it’s not always a sign of end times. Sometimes the heater is merely telling you that it’s overwhelmed. Or, it could be a sign of dirt building, which is also something you can fix quickly.

However, furnace short-cycling during the cold weather can also be a sign of internal malfunction and one of the last stages before the furnace dies. So, it would help if you were prepared.

Let’s find out what causes furnace short-cycling in winter, the potential dangers, and how to address the problem.

What is Furnace Short Cycling?

Short cycling during heating essentially means that your furnace isn’t running a full heating cycling or that the heating cycling is too short going by industry standards.

An optimally functioning furnace cycles three to eight times per hour. A complete cycle comprises both the heating cycle and the off cycle. So, if a furnace heats for 10 minutes and cycles off for the next 10 minutes before resuming the heating cycle, the whole cycle amount to 20 minutes. Therefore, such a furnace will have three complete cycles per hour. The majority of furnaces operate at this rate during regular operation.

However, some units are cycle ON-OFF faster. So, you’ll find some completing an entire cycle in less than 10 minutes, i.e., five minutes ON and five minutes OFF. These models complete up to six full cycles per hour. This is still considered normal. So, even eight cycles are within range.

However, it becomes abnormal as soon as your furnace starts running nine or more cycles per hour. A furnace that completes that many cycles per hour is said to be short-cycling.

Dangers of Furnace Short Cycling

Although it might seem harmless, short cycling is a ticking time bomb. The following are common dangers furnace short cycling;

Ineffective Heating

The first main downside of furnace short cycling is heating inefficiency. Think about it. The furnace is designed to heat in well-defined cycles. For instance, perhaps your heater is built to cycle between 4-6 times per hour. It means that the furnace is most efficient within that range.

It produces enough heat within 5-10 minutes and distributes it evenly throughout the home such that it can cycle off for the next 5-10 minutes without negatively impacting indoor temperature.

Now, you’re asking the unit to cycle twice as fast! It won’t have enough time to produce enough heat to heat the room as needed.

Faster Wear and Tear

Another issue is wear and tear. Furnaces are delicate systems comprising multiple different parts that work together harmoniously to keep your home warm. The heat exchanger, for instance, is very delicate. Even slight stress can cause it to crack and, within a short time, malfunction.

In addition, whenever the furnace cycles off to prevent overheating, it puts extra strain on the heat exchanger. Every time it shuts off, it pushes the heat exchanger’s limits.

It means that too frequent on/off cycles would put extreme pressure on the heat exchanger. This usually causes the heat exchanger to wear very fast, crack, and start to leak.

Fluctuating Humidity 

Finally, short cycling can also affect humidity levels in your home. Remember that moisture levels in the home are directly related to indoor temperature. So when it’s warmer, the house feels more hydrated, and when it’s cold, your home also becomes a tad drier.

As we have seen, short cycling is one of the many issues that often affect indoor heating efficiency. It can cause under-heating when the furnace doesn’t get sufficient time to pump heat into the home.

If the home becomes colder, as a result, you may experience increased dryness as well. The constant On-OFF cycling can also cause constant swings of dry and hydrated conditions.

Causes and Solutions to Short-Cycling During Winter

The following are common reasons why your furnace may short-cycle during winter and recommended fixes.

1. The Furnace is Overheating

Modern furnaces automatically cycle off if the unit becomes too hot. Manufacturers reason that for the furnace to become too hot, it would mean that your home is also sufficiently warm. They also want a way to protect the unit from damage. Therefore, cycling off seems like a well-reasoned solution.

The furnace can overheat for a range of reasons. Perhaps the filter is dirty, or airflow is impeded. Whichever the case, the heater will short cycle to try to avert further risk.

Solution: Begin by ensuring the filters are clean and clearing the vents to ensure unimpeded airflow. If the two fixes don’t work, it’s time to call the professionals.

2. It’s an Issue with the Thermostat

The furnace gets instructions from the thermostat. It’s the thermostat that tells it when to run and when to stop. It’s also the thermostat that tells it when to speed up or slow down. As a result, a thermostat malfunction can cause all sorts of confusion.

The thermostat usually causes short cycling when it has malfunctioned or is installed in the wrong location. If it has malfunctioned, it can wrongly signal the furnace that the set temperatures have been reached even when the room is still cold. This can cause the furnace to stop too frequently. A thermostat located in a warm place can also signal the furnace to cycle off even when the rest of the room is still cold.

Solution: The first step is to ensure the thermostat is located where it depicts the average temperature of the room. Additionally, make sure it hasn’t malfunctioned. Both of these may require professional input.  

3. The Furnace is too Big

Did you check the furnace’s size when buying vis-a-vis the size of the application? For example, if your home is 3,000 square feet, did you verify that the thermostat is sized for homes in that range? If you didn’t, the short cycling could be because the heater is too big for your home.

You see, heaters are designed with a specific home size in mind. That’s why we have all heater sizes, from under 10,000 BTUs to over 60,000 BTUs. A 10,000 BTU heater best suits rooms in the range of 350 to 400 square feet, while a 60,000 BTU furnace is designed for 2,000 square foot homes.

If you bring a 60,000 BTU heater to a 500 square-foot room, it reaches the thermostat setting faster. This is because furnaces cycle off immediately they reach the thermostat setting. So, that’s how you’d end up with short cycling.

Solution: The only solution here is to check whether you have the correct size furnace. You can verify it yourself by checking the sizing recommendation in the product’s user manual against your home size. Alternately, call an HVAC professional to help.

Key Takeaway

Furnace short cycling during the cold weather isn’t uncommon. It happens quite a lot. More importantly, it’s dangerous. Apart from causing heating inefficiency in the home, thus compromising indoor comfort, short cycling can overwork and ultimately damage your furnace.

Fortunately, you can address the most common causes of short cycling with ease. Just make sure the furnace isn’t oversized, ensure the thermostat is working optimally, and regularly maintain the furnace to prevent dirt buildup.