When the temperatures finally start dropping in Raleigh, Durham, and the surrounding Triangle area, homeowners start turning on their heat for the first time in months.
And almost immediately, the questions begin.
Why does my heat smell like it’s burning? Why is my outdoor unit running when the heat is on? Is that smoke coming from my heat pump? Why does my thermostat say AUX HEAT?
The good news is that many of the things homeowners notice during the first few heating cycles of the season are completely normal. Others can be signs that your HVAC system needs to be inspected.
Here are some of the most common questions we hear when homeowners turn on their heat for the first time each fall.
Why Does My Heat Smell Like It’s Burning When I First Turn It On?
A slight burning or dusty smell is very common the first time you turn on your heat after the summer.
During the warmer months, dust can accumulate inside your furnace or on heating components. When the heat turns on for the first time, that dust heats up and can create a temporary burning smell.
In many cases, the smell should begin to disappear after the system has run for a little while.
However, not every burning smell should be ignored.
Turn the system off and have it checked if you notice:
- A strong electrical or melting-plastic smell
- Visible smoke
- A smell that continues instead of improving
- Unusual noises along with the smell
- Your system shutting off unexpectedly
When in doubt, it is better to have an HVAC technician inspect the system.
Why Is My Outdoor AC Unit Running When the Heat Is On?
If you have a heat pump, this is completely normal.
Unlike a traditional gas furnace, a heat pump uses your outdoor unit during both the cooling and heating seasons.
In the summer, the system moves heat out of your home. During the winter, it essentially reverses the process and transfers heat from outside into your home.
So if your thermostat is set to HEAT and you hear your outdoor HVAC unit running, it does not necessarily mean something is wrong.
If you’re unfamiliar with how heat pumps work, ENERGY STAR has a helpful overview explaining how these systems provide both heating and cooling.
Why Is There Smoke Coming From My Heat Pump?
What looks like smoke coming from your outdoor heat pump may actually be steam from the defrost cycle.
Heat pumps can develop frost on the outdoor coil during cold weather. When the system enters defrost mode, it temporarily warms the outdoor coil to melt that frost.
When moisture hits the warmer coil, you may see a large cloud of steam coming from the unit.
It can look dramatic, especially on a cold morning, but a brief cloud of steam during defrost is generally normal.
However, if you smell burning, see actual smoke, or notice another unusual condition, turn the system off and contact an HVAC professional.
Why Is There Frost or Ice on My Outdoor Heat Pump?
A small amount of frost on a heat pump during cold weather can be normal.
Your heat pump should periodically enter a defrost cycle to remove it.
What is not normal is an outdoor unit that becomes heavily covered or completely encased in ice and stays that way.
Excessive ice buildup can sometimes be caused by problems such as:
- A defrost system problem
- Restricted airflow
- Refrigerant issues
- A malfunctioning outdoor fan
- Drainage or moisture problems
If the ice continues to build instead of disappearing during normal operation, it is worth having the system checked.
Why Doesn’t the Air From My Heat Pump Feel Very Hot?
This is one of the most common concerns we hear from homeowners who are used to a gas furnace.
A furnace can produce noticeably hot air at the vents.
A heat pump works differently and may produce air that feels warm rather than hot.
Because your body temperature is around 98 degrees, air coming from the vents can sometimes feel surprisingly mild against your hand even while the system is successfully heating your home.
The better question is whether the home is reaching and maintaining the temperature you have set on the thermostat.
If your heat pump is running but the indoor temperature continues dropping or never reaches the thermostat setting, there may be a problem.
Why Is My Heat Running for So Long?
Longer heating cycles are not automatically a sign of an HVAC problem, especially if you have a heat pump.
Heat pumps are designed to provide steady heating and may run longer than a gas furnace, particularly when outdoor temperatures are colder.
You should be more concerned if:
- The system runs constantly but the house does not get warmer
- Indoor temperatures continue falling
- The system repeatedly turns on and off every few minutes
- Your energy usage suddenly changes dramatically
- Certain rooms are no longer heating properly
Those symptoms may indicate that your system needs service.
What Does AUX HEAT Mean on My Thermostat?
If you have a heat pump, you may occasionally see AUX HEAT, AUXILIARY HEAT, or a similar message on your thermostat.
Auxiliary heat is a secondary heat source that helps your heat pump when it needs additional heating capacity.
It may come on automatically when:
- Outdoor temperatures are especially cold
- Your thermostat temperature is raised several degrees at once
- Your heat pump is going through a defrost cycle
- The heat pump cannot keep up with the thermostat setting on its own
Seeing AUX HEAT occasionally does not necessarily indicate a problem.
However, if auxiliary heat seems to run constantly during relatively mild weather, your system may need to be inspected.
What Is the Difference Between AUX Heat and Emergency Heat?
These two thermostat settings are often confused.
Auxiliary heat usually comes on automatically when your heat pump needs additional help.
Emergency heat is typically a setting you manually select. It bypasses normal heat-pump operation and relies on the backup heating source.
Emergency heat generally should not be used simply because it is cold outside. If your heat pump is operating normally, allow the system to control auxiliary heat automatically.
If you believe the heat pump itself has failed, contact an HVAC professional.
Why Did My Electric Bill Go Up After Turning On the Heat?
Heating can significantly change your home’s energy usage, particularly during colder weather.
For homes with heat pumps, frequent use of electric auxiliary heat can increase electricity consumption because electric resistance heat typically requires substantially more energy than normal heat-pump operation.
A higher bill does not automatically mean your HVAC system is malfunctioning, but unusually high energy usage combined with constant AUX HEAT, poor heating, or unusually long runtimes may be worth investigating.
Why Does My Heat Pump Make a Whooshing or Hissing Noise?
Some unfamiliar sounds can occur when a heat pump changes operating modes or enters a defrost cycle.
Homeowners sometimes notice:
- A brief whooshing sound
- A hiss
- A change in compressor sound
- The outdoor fan stopping temporarily
- Steam appearing around the outdoor unit
These can all occur during normal heat-pump operation.
Loud grinding, banging, screeching, or other persistent mechanical noises should be inspected.
Should My Thermostat Fan Be Set to AUTO or ON During Heating?
For most homeowners, AUTO is the normal thermostat fan setting.
When the fan is set to AUTO, the blower runs when the HVAC system is actively heating or cooling.
When the fan is set to ON, the blower may run continuously even when the system is not actively heating.
That can sometimes make homeowners think their heating system is running nonstop when they are actually hearing only the indoor fan.
Should I Change My Air Filter Before Turning On the Heat?
The beginning of heating season is a great time to check your HVAC filter.
A dirty filter can restrict airflow and make your system work harder.
How often a filter needs to be changed depends on factors such as:
- Filter type and thickness
- Pets
- Number of people in the home
- Indoor air quality
- How frequently the HVAC system operates
Do not rely only on a calendar. Check the filter regularly and replace it when it becomes dirty.
Should I Schedule Fall HVAC Maintenance If My AC Worked Fine All Summer?
Cooling properly during the summer does not necessarily mean every component needed for heating is operating correctly.
Depending on the type of HVAC system you have, a heating maintenance visit may include checking components related to:
- Furnace ignition
- Burners
- Safety controls
- Electrical components
- Heat-pump operation
- Defrost operation
- Airflow
- Thermostat operation
Finding a heating problem before the first freezing night is usually much more convenient than discovering it when your home suddenly will not heat.
When Should You Call an HVAC Company?
Some strange smells, sounds, and operating behaviors are normal when you first turn your heat on.
Others should not be ignored.
Consider scheduling HVAC service if:
- Your heat will not turn on
- Your home will not reach the thermostat temperature
- You smell a strong electrical or melting smell
- You see actual smoke
- Your heat pump stays covered in ice
- The system repeatedly turns on and off
- You hear loud or unusual mechanical noises
- Your auxiliary heat runs excessively
- Your system is running but blowing cold air continuously
If you’re unsure whether something you’re seeing is normal, an HVAC technician can help determine whether your system simply needs time to transition into heating season or whether there is an underlying problem.
Heating Service in Raleigh, Durham and the Triangle
If you’re turning on your heat for the first time this fall and something doesn’t seem right, Klimatology HVAC provides heating repair, maintenance, and HVAC service throughout our service area in the Raleigh-Durham Triangle.
Whether you have a gas furnace or heat pump, our technicians can inspect the system, identify any problems, and help make sure your home is ready for colder weather.
Need your heating system checked? Contact Klimatology HVAC to schedule service.
