Emergency heat generally costs more to operate than the regular heat mode, often by a significant margin, but exactly how much depends on your heating system and energy prices. Here’s a concise guide to understanding the difference and how to estimate it for your situation. Core idea
- Emergency heat (often called AUX or EM heat) uses a secondary heat source, such as electric coils, when the primary heat source (the heat pump) is unable to meet the demand efficiently. This secondary mode typically consumes more energy, leading to higher bills [citations will be provided from tool results if needed, see note below].
What drives the cost difference
- Energy source: If the secondary heat is electric coils, electricity costs will dominate, which can be much higher per unit of heat than the energy used by the heat pump’s normal operation. If your secondary system uses gas or oil, the cost dynamics shift to fuel prices and efficiency.
- Outdoor temperatures: As outdoor temperatures plummet, the heat pump loses efficiency and may rely on emergency heat more, increasing energy use.
- Duration: The longer emergency heat runs, the larger the impact on the bill. Short bursts during cold snaps are less costly than extended use.
- System efficiency: Modern heat pumps with efficient auxiliary heat control reduce unnecessary cycling, but the fundamental reason emergency heat costs more remains the higher energy draw of the secondary heat source.
Estimating the cost difference
- Know your energy rates: Find your current electricity rate (cents per kWh) and, if applicable, any gas/oil fuel costs.
- Determine heat output and usage: Check your thermostat or energy logs to estimate how many hours emergency heat runs in a typical cold period.
- Rough rule of thumb: In many cases, emergency heat can cost roughly 2–3 times as much to operate as normal heat, especially when electric resistance heat is used as the secondary source. This is a common benchmark cited by HVAC resources, though exact multipliers vary by system and energy prices.
- Practical approach: Compare your monthly bills with the heat pump in normal operation versus when emergency heat was active, noting the percentage delta during similar weather conditions. If you use a utility portal, you can often download hourly usage data to isolate the heat-related consumption.
What you can do to minimize cost
- Use emergency heat sparingly: Reserve it for truly critical moments and allow the heat pump to recover as soon as outdoor conditions permit.
- Improve heat pump efficiency: Ensure filters are clean, refrigerant levels are correct, and the outdoor unit is free of obstructions; regular maintenance can keep the heat pump operating closer to its rated efficiency.
- Maximize thermostat strategy: Set reasonable, consistent indoor temperatures and avoid large temperature swings that cause the system to rely on emergency heat more often.
- Consider upgrades: If emergency heat is a frequent necessity, discuss with an HVAC pro whether higher-efficiency secondary heat options (e.g., a more efficient gas furnace or better-integrated heating strategy) would be cost-effective for your home.
If you’d like, provide:
- Your electricity rate and, if applicable, any natural gas or fuel oil costs.
- Your typical winter outdoor temps and indoor setpoints.
- The make/model of your heat pump and secondary heat source.
With those, a more precise estimate of the expected cost difference for your situation can be calculated.
