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Ever checked the thermostat and seen an AUX icon that indicates that auxiliary heat is displayed on the thermostat? If yes, then most likely panic over the possibility of escalating utility bills immediately hit. Worry no more, we at Reliable Standard Heating and air will explain through this article what that AUX Icon is all about, what auxiliary heat means, why it would suddenly appear in the thermostat, and how to deal with this.

But before discussing auxiliary heat, it is best to know how the heat pump works. By knowing the ins and outs of distributing heat throughout the house, it will be easier to understand the reasons why AUX will suddenly appear on the thermostat’s screen.

How does a heat pump work?

The heat pump does the reverse work of an air conditioner. It basically takes heat from the outside and brings it indoors through the various air registers inside the house. It consists of an outdoor unit called the condenser, and an indoor unit called the air handler. The condenser circulates the refrigerant to transfer heat much like the operational system of a refrigerator. During the summer, the heat pump does the opposite as it transfers heat energy from inside the house, towards the outdoors so that the air will be colder and more comfortable indoors.  The reverse valve is responsible for this dual type of action.

During the winter season, the heat pump utilizes a substance called refrigerant to absorb the heat from the air outdoors. Once the heat energy is absorbed, it is pressurized in the heat pump’s compressor so that it could transform into vapor. Once it entered the gaseous state, it will be transferred to the air handler unit. It will then get transferred to the indoor coil. Once this happens, the cold air indoors will get blown through the coils and consequently absorb the heat. As heat is removed from the refrigerant, the substance will transform into liquid, and get re-circulated within the heat pump’s system.

So, what does this all have to do with auxiliary heat?

Within the air, the handler is the electric heating element, referred to as electric resistance heating, and is a source for supplemental heating. Various models of heat pump may have the electric heating element as responsible for both emergency heating and auxiliary heating. This is rather expensive though compared to the usual way of heating the house and is just usually used when there is an issue with the usual heating process.

The usual issue involves a frozen heat pump, which is actually a serious problem for any heating system.

What is auxiliary heat?

It will help to remember that auxiliary and emergency heating are settings within any thermostat that would activate the electric heating element of the heat pump. However, keep in mind that there are heat pump brands and models that do not have both. Some may just have the auxiliary heating option, while other models only come with emergency heating. For owners who have lived in homes that have heat pumps that only have one of those options, the two terms can be used interchangeably.

Auxiliary heating 101

As the name suggests, auxiliary heating is a feature of a heat pump that ensures adequate heating even in the coldest of winters. It helps the heat pump generate the desired level of warmth inside the house when the heat pump cannot function to produce such. It is the thermostat that activates the auxiliary heating system upon detecting that the heat pump cannot provide the desired temperature on its own within twenty minutes or so. Usually, this is activated automatically as it is already pre-programmed by the heating system. However, some units allow the manual setting of the auxiliary heating process.

Once the desired temperature is reached, the auxiliary heating feature will shut off on its own. However, if the auxiliary heat does not shut off, it is indicative of a problem within the heating system.

All about emergency heat

Emergency heat which has the “em heat” indicator in most thermostats, is an emergency heating feature of a heat pump. Like auxiliary heating, it makes use of electrical heating strips to provide warm air indoors. The key difference between auxiliary heating and emergency heating though is that the latter is not automatically triggered. It does not activate right away. The homeowner must manually choose emergency heating upon noticing a problem with the heat pump.

Like auxiliary heating, it can be very expensive to utilize emergency heat, so it is best to use it only when it is extremely necessary. Seek professional repairs right away to avoid skyrocketing utility bills.

When to turn on the emergency heat function

A homeowner should only turn on the emergency heat mode when the heat pump cannot reach the desired temperature within 25 to 30 minutes of setting it. Monitor the thermostat to check this. If the heat pump has both auxiliary heating and emergency heating features, and the temperature cannot be reached even though the auxiliary heating has kicked off, then it is time to turn on the emergency heat mode.

It is best to call an HVAC professional as soon as emergency heating is activated to avoid enormous heating bills. However if nothing is working, see why your furnace is not blowing warm air and what you can do about it.

How to know if auxiliary heating is triggered

The easiest way to determine if auxiliary heating is turned on is by checking the thermostat. The word AUX will be displayed on the panel to indicate that the feature has been automatically triggered by the heating system.

What causes auxiliary heat to turn on?

There are several reasons why auxiliary heating will be triggered. Below are some of the most common situations, and what it means.

Cold weather triggers auxiliary heating

When the temperature goes lower than 40, the heat pump or the main heating system loses operational efficiency. This is because the heat pump cannot usually generate enough hot air from outside the house when the weather is too cold. As mentioned in the earlier portion of this article, a heat pump gathers heat from the outside, processes it, and distributes it indoors to warm the whole house. When temperatures drop way low, it cannot reach the usual desired temperature indoors and will need help from the auxiliary heat.

Fortunately, auxiliary heating will turn on its own once the desired temperature has been reached. If it stays on for much longer then chances are there is a problem with the heat pump’s mechanism. Call for HVAC repair to straighten out the matter right away. Letting AUX heating operate for much longer will make utility bills costlier.

Setting thermostat levels higher can trigger auxiliary heating

Raising thermostat levels much higher can trigger the use of auxiliary heating. Usually, when the adjustment is about three degrees higher or more, auxiliary heating will turn on to help out the heat pump meet the temperature level required by the household.

When the heat pump is in defrost mode

The auxiliary heat will get triggered whenever the heat pump gets into defrost mode. Usually, during very cold months, the heat pump can accumulate ice. There however are times when the frost is way too much that it hampers the ability of the heat pump to provide heat throughout the home.  When this happens the heat pump’s control board signals the operating system to trigger the reverse valve, so it could send the hot refrigerant toward the frozen condenser coils to thaw the ice.  This cycle is usually called the defrost mode, and whenever this operational procedure is occurring, the heat pump will need the help of auxiliary heating to provide warmth for the whole home.

How long should the auxiliary heat work?

The normal time range that the auxiliary heat should run is likened to the period It takes for the thermostat to reach the desired temperature. If the answer to this is 30 minutes, then AUX should run for about this time and automatically turn off right after.

If in case auxiliary heating runs much longer than this, is turned on for the whole day, or gets triggered each time heat is turned on, then it is time to call for an HVAC repair. It is not normal for AUX heating to get triggered the whole time, and any prolonged usage should merit professional attention right away.

Why does the auxiliary heat stays turned on

Auxiliary heat is just a mechanism that ensures the heat pump can keep the whole house warm during freezing cold temperatures. However, if it operates for much longer then it is highly likely that there is something wrong with the heat pump. Below are some of the common reasons why an auxiliary pump would stay on for prolonged periods.

Malfunctioning Condenser Fan Motor

The condenser fan is responsible for circulating air from the motor toward the coils. If it is faulty, then, the heat pump cannot suck up enough heat to meet the temperature levels indicated in the thermostat. So any issues with the condenser fan motor could affect the heat pump’s operations since it affects airflow within the heating system. Sometimes, the fan could just be covered in filth, sometimes it is broken, and oftentimes it is just worn out or lacks maintenance. Whatever the case may be, it can trigger the operation of the auxiliary heating.

Low levels of refrigerant

Ideally, heat pumps and air conditioners should not run low on refrigerant since it operates in a closed unit and just get used over and over again. However, there are times when the heat pump or AC is incorrectly installed, the pipes incur damage and give way to leaks, and mechanisms get worn out. When such things occur, refrigerant can leak and run low. And when the system is low on refrigerant, the heat pump cannot meet the temperature requirement of the household, triggering the need for auxiliary heating. So, when auxiliary heating is triggered and refrigerant levels remain low, it will remain turned on for a prolonged period and will rake in higher utility bills.

Failing compressor

The compressor is one of the most crucial parts of a heat pump. It paves the way for the refrigerant to turn into liquid from its original gaseous state so that it can help generate heat indoors. When it fails, it can surely affect the heat pump’s ability to warm the whole house. When the compressor falters, the condenser can no longer transfer heat to the indoor air handler and consequently fail to warm the whole house. Because of this, auxiliary heating will get triggered and will stay turned on until the issue is resolved.

For this reason, homeowners should immediately call for HVAC repair, to prevent a dramatic rise in utility costs and worsening of the existing issue.

Malfunctioning defrost control board

When the defrost control board fails to correctly function, auxiliary heating will get triggered. A malfunctioning defrost control board means the ice build-up in the heat pump will not get thawed out, hindering its normal heat-generating functions. When the heat pump fails to deliver the desired indoor temperature, the auxiliary heat will get automatically triggered and will remain turned on for much longer. A bad board could be the reason why your furnace is blowing cold air in the first place.

Issues with the reversing valve

The reversing valve is a mechanism within the heat pump that prompts a change of direction of the refrigerant. When the reversing valve is triggered, the hot refrigerant should thaw out the icy coils in the condenser unit so that the heat pump can function correctly and deliver the required temperature. If it is faulty, the heat pump will work on cooling mode consequently triggering the auxiliary heating. This will surely bore a hole in the pocket given that the heat pump and auxiliary heating seem to be competing with each other.

How to stop auxiliary heating from turning on

There is no way to prevent auxiliary heating from getting triggered if the home is located anywhere where temperatures could dip to 40 degrees or lower. Auxiliary heating is a normal feature that helps out the heat pump in providing warmth whenever it struggles to produce heat due to extreme cold weather outdoors.

The best question to ask though is how to keep auxiliary heating from working for a prolonged period or from getting triggered even if the temperature outdoors is not below 40. The simple answer to this concern is to keep the heat pump well-maintained.

The usual issues that activate auxiliary heating are heat pump problems that are easily avoided due to lack of maintenance. By having a bi-annual professional maintenance check, operational issues like the prolonged operation of the auxiliary heating system can be avoided.

Do not crank up the temperature too much

Keeping the temperature levels low will help keep auxiliary heating operations at bay. When it is suddenly too cold outside, some homeowners tend to crank up the heat. Raising the temperature by 3 degrees or more will trigger the use of the auxiliary heating system. If the weather outside is lower than 40 degrees, and the heat is cranked up then definitely the heat pump will struggle in providing the required temperature levels.

The best range of temperature that will keep auxiliary heating from getting triggered is by setting indoor thermostat levels between 61 to 68 degrees.

Avoid malfunctioning and prolonged auxiliary heating with routine professional tune-ups

Professional maintenance and servicing are key to avoiding malfunctioning within the heat pump system. Like any other appliance that works 24/7, the heat pump also incurs wear and tear, and damage due to aging. With routine maintenance, these potential issues are kept at bay as they are resolved even before they can cause inconvenience and discomfort.

During a routine professional tune-up, the HVAC repair team will assess and inspect the operational functionality of each of the mechanisms of the heat pump. During this assessment, the technicians will gain a better understanding of which parts are optimally functioning, and which are failing. They will then address any concerns, proceed to provide a thorough system clean-up, and make necessary adjustments and greasing needed for every part to function optimally. By being one step ahead of potential heating problems, the homeowner gets to prevent the heat pump from tapping into auxiliary or supplemental heating, which is more expensive to use. Instead, do you see water leaking from your furnace? You may be wondering why your heater is leaking water and what you can do about it.

Restore efficient heating with an HVAC Professional

If the auxiliary heating icon keeps on popping up in the thermostat panel or is there for a much longer period then it is time to call for professional HVAC repair. We at Reliable Standard Heating, Air, & Solar will be more than happy to help out with any of your heating concerns. You can rely upon us too for your routine heat pump tune-ups! Get in touch with us today.

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