What is AUX Heat on my Heat Pump?

AUX Heat or EM Heat on the thermostat
Nest thermostat in AUX Heat mode

How Your Heat Pump Works

Heat pumps are incredible feats of engineering, but like most appliances have their limits. Heat pumps provide very energy efficient heating when compared to traditional electric central heating air handlers, but due to the science behind their design can only go so far.

We spoke in detail about how your heat pump works on an earlier blog, which you can read here. But I will go ahead and give you a quick summary.

In cooling mode your HVAC system uses the evaporator coil inside your home to absorb the heat in the air (into the refrigerant) and then sends the heat to the condenser/outdoor unit and rejects the heat (from the refrigerant) and then starts the process back over. Pretty simple.

With a heat pump, when you switch to heat mode your HVAC system reverses the flow of refrigerant. Now your condenser/outdoor unit is absorbing heat from outside (into the refrigerant) and sends the heat indoors to the evaporator coil and rejects the heat (from the refrigerant) into your home.

Heat Pump Limitations

The limitation of the heat pump is based on the science of refrigerant. The temperature of the refrigerant in your condenser, when in heat mode, is between 35-42 degrees. Heat transfers from the warmer object to the colder one, which means that if it is below that 35-42 degree temperature your condenser is giving off heat, not absorbing it. When this happens there is no heat in the refrigerant to reject inside your home and your heat pump blows cold air.

The Purpose of AUX Heat

This is where AUX heat, or EM heat (emergency heat) comes into play. Inside the air handler (indoor unit) of every heat pump are electric heat strips. These work just like an electric stove. When energized the resistance of the heat strips causes the strip to get hot and glow bright red. As your blower motor moves air across these strips the air gets warm and circulates through your home.

The purpose of AUX heat/ EM heat is to supplement your heat pump on days when the temperature gets below 35-42 degrees. Some thermostats can be programmed to make the switch automatically based on an outdoor ambient heat sensor, others need to be switched over manually. If you notice that your heat pump is blowing cold air from the vents when in heat mode, check the outdoor temperature. If it is below the 35-42 degree window switch your thermostat over to AUX heat or EM heat.

AUX Heat As A Backup

AUX heat or EM heat also operates as a back up in case anything goes wrong with your heat pump. If the refrigerant leaks out, or the condenser has a failure you can simply switch to AUX heat and remain warm until repairs can take place.

If you have any questions or concerns regarding your heat pump or HVAC system in general and live in the Fort Worth area give us a call, we’d love the opportunity to serve.

If you want to learn a bit more about your evaporator coil check out one of our videos here.

Prestige Air proudly serves Northeast Tarrant County and the Fort Worth, Texas area including Hurst, Euless, Bedford, Colleyville, Grapevine, Southlake, Keller, Watauga, Haltom City, and North Richland Hills.

We look forward to serving you and your household!

Share the Post:

Let Us Help You!

At ​Prestige Air, we’re a team full of passionate heating and air conditioning technicians who care deeply about our clients. We know that issues with your heating and cooling can be a headache and our goal is to get your issues resolved ASAP so you can get back to living your life stress-free.

Contact us using the form below or feel free to call us directly at (817) 200-7215. We’d love the opportunity to serve you!

Save $50

On your first service
When You Book Online Today

Simply mention this popup and we’ll take $50 off of your first service.

Or call us if you have questions (we’ll still honor the discount)