EM heat stands for "emergency heat" and is a setting on your thermostat that controls your homes backup heating system. If you have this setting, you likely have a heat pump and a secondary heating source, such as gas, oil, electric, or hot-water. The emergency heat setting is used when your heat pump needs a break to avoid system damage, or when the temperature is extremely cold outside and the heat pump is struggling to pull in heat.
When you manually set the emergency heat on your thermostat, your system bypasses the heat pump and directly accesses either the electric heat strip or the gas or oil furnace. This is especially useful on extremely cold days when you need to quickly heat your home in an emergency situation. However, its important to note that using emergency heat mode constantly can raise your energy bills like crazy.
Its also important to understand the difference between "aux heat" and "em heat" on your thermostat. Auxiliary heating is an automated function that turns on when the outdoor temperature takes a quick dip, and it typically only runs for up to a couple of hours. When auxiliary heat is activated, your heat pump energizes a heat strip within its system for an added heating boost. On the other hand, when you activate emergency heat, the primary system is bypassed entirely, so instead of having both systems working in tandem to generate excess heat, you are only able to use the backup heating source.
In conclusion, EM heat is a backup heating system that acts as a backup in case your primary heating system fails. Its important to understand how to properly use it and not just switch it on without understanding its purpose.
