(NEXSTAR) – With frigid temperatures, ice and snow in the forecast for much of the U.S. this week, heaters practically everywhere are going to be working overtime. If you're not feeling the warmth, HVAC experts say you may need to switch the mode on your thermostat. Many thermostats have a setting called EM heat, emergency heat or auxiliary heat. You shouldn't normally rely on it warm your house, but it's useful when the thermostat's regular settings aren't cutting it. In normal conditions, your heat pump is the primary worker. But in below-freezing temperatures, or when a unit’s heat pump malfunctions, this is where the EM heat setting comes in handy. Will heating bills be higher this winter? It depends on where you live A lot of times, this backup system switches on automatically if it's particularly cold outside. But if you've turned up the heat and your home or apartment keeps getting colder and colder, you might want to switch on emergency heat manually. A thermostat shows auxiliary heat activated, which may happen automatically in ultra-cold weather. (Photo: Getty Images) You can continue using emergency heat while you wait for a service technician to come take a look, or while you wait for your heat pump to defrost. Should you set heat to a constant temperature or turn it on and off? “This is way less efficient than your primary heating system, so you should only use it in real emergencies unless you want to pay exorbitant heating bills," explained Valley Service, a North Dakota HVAC company, in a 2021 post. If you find yourself switching to emergency heat, you'll want to call for repairs too. It should only be used to avoid your house from getting too cold while you wait for help fixing up your primary system.