Does it seem like the heat turns off before it really gets started? If it does, your furnace is probably short cycling.
A short-cycling furnace can make it hard to stay comfortable during the winter. When your furnace won't complete a typical cycle before shutting off, you might also be wondering why it's happening and what to do about it.
Let's take a look at why furnaces short cycle. We'll also look at some ways to address the problem and prevent it going forward.
Is a short-cycling furnace really a problem?
Yes, a short-cycling furnace is a problem. Here are some reasons why:
- Your house won't get comfortable. Since the furnace only runs for a short period of time, it might fail to properly distribute warm air throughout your home.
- You'll have hot and cold spots. This is related to the point above. When your furnace only runs for a short period of time, it might blast warm air around areas near supply vents. Unfortunately, it's not running long enough to move the warm air to the rest of the home, resulting in some areas that are hot and others that are cold.
- Short-cycling is hard on your furnace. A short-cycling furnace experiences excess wear and tear, leading to more frequent problems and premature failure.
- It's hard on your wallet, too. Furnaces consume the most energy when they turn on from being idle. A short-cycling furnace turns on from idle more often than one that runs for longer cycles, so your winter heating bill is higher.
So, you definitely do not want your furnace to short cycle. But why does it happen in the first place?
Reasons why furnaces short cycle
There are a few different reasons why any given furnace will start short cycling.
The furnace is too big.
If you'll pardon the pun, this is the "biggest" contributor to short cycling furnaces in homes we service. Many HVAC contractors oversize the furnace (actually, they oversize the entire HVAC system), resulting in truncated furnace run cycles.
Having an oversized furnace is not good.
When the furnace is too large, it moves a lot of hot air into your home very quickly. As a consequence, it satisfies your thermostat setting really soon after it turns on. This leaves you with the problems discussed in the section above: hot and cold spots, excess wear and tear, chronic discomfort, and so on.
The best solution is to replace the oversized furnace with a properly sized one. To do so, your HVAC contractor must-and this is not optional-perform a Manual J load calculation prior to selecting equipment.
Oversizing happens when contractors guess at the right size for your furnace. Proper sizing is what happens after a load calculation.
The flame sensor is dirty.
When this component of a furnace is dirty and can't operate properly, it will shut the furnace off. This is actually a safety feature.
While this isn't short-cycling, per se, it can seem like your furnace short-cycled if it turns on and then turns off again really quickly due to the dirty sensor.
The solution? Have your furnace serviced once per season. That way, the flame sensor and other furnace components will enjoy a good cleaning!
As a PV Priority Plan member, you get two service visits per year for a single low price. Members also enjoy priority service, parts discounts, and waived service charges!
The hot surface igniter is malfunctioning.
If the hot surface igniter is broken, the furnace will shut off for safety reasons. This is similar to what happens when you have a dirty flame sensor, although it happens because of a problem with a different component.
The solution is to have a professional replace the hot surface igniter.
Your thermostat is broken.
Occasionally, we'll encounter a thermostat that isn't working properly. It might sense that the temperature setting has been satisfied even if it hasn't, resulting in early furnace shutoff.
If you suspect this is the problem, change your thermostat batteries. If that doesn't solve the problem-and we've determined that your thermostat is responsible for the short cycling furnace-you can replace the thermostat.
How to prevent your furnace from short cycling
The best ways to prevent a furnace from short cycling depend on why it's short cycling in the first place.
Since the most common cause of a short cycling furnace is being oversized, you can solve that problem by replacing the unit.
Of course, you might not want to do that just yet. Maybe the furnace isn't all that old. We get it.
The best thing to do is keep your air filter clean to optimize airflow. Aside from that, maybe consider supplemental heating from a mini-split heat pump until it's time to replace the furnace with a properly sized one.
However, if the problem has to do with dirty components or broken parts, have the furnace serviced! Annual pre-heating season maintenance visits can help you avoid the most serious furnace problems all through the winter season.
Conclusion: Different furnaces short cycle for different reasons.
And there's always a solution!
The way we see it, you deserve not to live in a home with lots of hot and cold spots. You deserve to be cozy and comfortable during the winter months!
If you live in Metro Atlanta and are concerned about a short-cycling furnace, PV Heating, Cooling & Plumbing can help!
Call us today at (404) 798-9672 or schedule an appointment online!
