As a Maryland homeowner with a heat pump, you appreciate its efficiency for most of the year. But when the winter cold truly sets in, you might notice the AUX or emergency heat light on your thermostat. Seeing the emergency heat on occasionally is normal, but if it seems to run constantly, it’s natural to worry about what that use means for your comfort and your utility bills.
Sometimes, your heat pump switching to auxiliary heat is a normal part of its operation, designed to keep your home warm when temperatures drop. However, frequent or constant use can signal an underlying problem that needs professional attention.
Understanding Your Heat Pump’s Auxiliary Heat Function
A heat pump works by transferring heat. In winter, it extracts heat from the outdoor air and moves it inside.
When it gets too cold outside for the heat pump to extract enough heat to warm your home, the auxiliary heat system kicks in to help. In most Maryland homes, this auxiliary system is a set of electric resistance coils that are similar to the glowing wires in a toaster. This component is built directly into your indoor air handler unit.
Electric heat isn’t as energy efficient as the heat pump itself, but it provides a powerful and reliable source of warmth when needed.
When Is It Normal for Auxiliary Heat to Activate?
In several specific situations, seeing your auxiliary heat turn on is expected and indicates your system is working as it should. Maryland winters can create these exact conditions.
During Extreme Maryland Cold Snaps
Every heat pump has a balance point, which is the outdoor temperature at which the unit can no longer produce enough heat to meet your thermostat’s setting. This point is typically between 30 and 40 degrees Fahrenheit. When the temperature outside dips below this balance point, your system will automatically activate the auxiliary heat strips to make up the difference and maintain your desired indoor temperature.
When Your System Enters Defrost Mode
During cold, damp weather, frost or ice can form on the coils of your outdoor heat pump unit. This buildup restricts airflow and hinders the heat transfer process. To combat this, your heat pump will periodically run a defrost cycle. To prevent cold air from blowing through your vents during this process, the auxiliary heat engages to keep your home comfortable.
For a Rapid Temperature Increase
If you manually increase the temperature on your thermostat by three degrees or more at once, the system may interpret this as a demand for a large amount of heat quickly. To satisfy this request as quickly as possible, it will often turn on the auxiliary heat strips along with the heat pump.
Signs Your Heat Pump Is Relying on Auxiliary Heat Too Often
While the situations above are normal, your auxiliary heat should not be running constantly or at all during mild weather. If you notice the AUX light is on more than it’s off, that’s a red flag. Constant reliance on this less-efficient heating method suggests your primary heat pump isn’t doing its job correctly.
Another major sign is a sudden, unexplained spike in your electricity bills. Because auxiliary heat uses significantly more energy than the heat pump, a malfunctioning system can lead to surprisingly high costs.
Common Reasons for Excessive Auxiliary Heat Usage
If your auxiliary heat seems to be working overtime, it’s often due to an issue that prevents your heat pump from operating at full capacity. Several common problems can cause this.
Incorrect Thermostat Settings
If the thermostat is accidentally set to “emergency heat” instead of “heat” or “auto,” it will bypass the heat pump entirely and only use the auxiliary electric strips. Always check that your system is set to the correct mode first.
A Clogged Air Filter
A dirty or clogged air filter is one of the most common causes of HVAC problems. It restricts airflow to the indoor unit, forcing the entire system to work harder. This strain can reduce the heat pump’s efficiency to the point where it can’t keep up, causing it to trigger the auxiliary heat to compensate for the poor performance.
Low Refrigerant Levels
Heat pumps rely on a precise amount of refrigerant to transfer heat. If the system has a leak and the refrigerant level drops, its ability to move heat from the outside to the inside is severely compromised. A system low on charge will struggle to heat your home, leading to long run times and frequent use of the auxiliary heat.
Outdoor Unit Obstructions or Icing
The outdoor unit needs unrestricted airflow to function. If it’s blocked by snow, leaves, or yard debris or if it’s covered by a tarp, the unit can’t absorb heat from the air. Similarly, if the unit is excessively iced over and the defrost cycle isn’t working correctly, it won’t be able to heat your home, forcing the auxiliary system to take over.
A Malfunctioning Compressor or Reversing Valve
The compressor and reversing valve are critical components of your heat pump. The compressor circulates the refrigerant, and the reversing valve switches the flow between heating and cooling modes. If either of these parts fails, the heat pump may lose its ability to heat effectively, making the auxiliary heat your only source of warmth.
An Undersized Heat Pump System
If a heat pump is too small for the size of your home, it will never be able to keep up with the heating demand, especially during a cold Maryland winter. An undersized unit will run constantly and rely heavily on auxiliary heat, leading to high bills and premature system failure. This is why proper system sizing during installation is so important for all modern heat pump systems.
Leaky or Inefficient Ductwork
Your ductwork is the delivery system for warm air. If you have leaks, gaps, or poor insulation in your ducts, a significant amount of the heat produced by your heat pump can be lost before it ever reaches your living spaces. Your system will run longer to compensate, and the auxiliary heat may kick on to try and overcome this heat loss.
Why You Shouldn’t Ignore Frequent Auxiliary Heat
Allowing your heat pump to rely too heavily on its auxiliary function can have significant consequences for your wallet and your system’s health.
- Dramatically higher energy bills
- Increased wear and tear on system components
- Inconsistent heating
- Reduced comfort
What to Check Before Calling for Service
Before scheduling a service call, there are a few simple things you can check on your own.
- Confirm the thermostat is set to “Heat”
- Replace a dirty air filter
- Clear debris from the outdoor unit
If you have performed these checks and your auxiliary heat is still running too often, it’s time to call a professional. Continuing to operate a malfunctioning system can cause more extensive damage.
Trust Maryland’s Experts for Your Heat Pump Needs
If your system is relying on auxiliary heat constantly, that’s a clear sign that something is wrong. From a simple clogged filter to a more complex component failure, a trained technician can accurately diagnose the root cause.
At Farnen & Dermer, our team has the expertise to identify why your system is overusing its backup heat and provide the right solution. Timely professional heat pump repair not only restores your system’s efficiency but also protects you from excessive energy bills and helps your home remain comfortable and warm all winter.
If you’re concerned about your heat pump’s performance, contact Farnen & Dermer today for expert heat pump repair services in Maryland.
