HVAC Operating Cost

Converting BTU Output and SEER Rating into an Electricity Cost

An air conditioner’s electricity cost comes from converting its BTU cooling output into an actual power draw, using its SEER efficiency rating. Enter your system’s BTU/hr output, its SEER rating, how many hours a day it runs, over how many days, and your electricity rate, and this calculator finds the total cost.

SEER measures how many BTU of cooling a system produces per watt-hour of electricity it consumes. A higher SEER rating means the same cooling output for less electricity — which is exactly why a more efficient (and often more expensive up front) unit can pay for itself in lower operating costs over its lifetime.

Key Factors to Consider

• “Hours per day” should reflect actual compressor runtime, not just how long the system is set to cool. A real system cycles on and off to maintain a set temperature rather than running continuously the whole time it’s active — entering the actual runtime hours (which can be well under a full day even in hot weather) gives a more accurate cost estimate than assuming continuous operation.
• SEER is a seasonal average, not a fixed efficiency at every moment. A unit runs somewhat less efficiently on the hottest days of the year than its SEER-rated average suggests, and more efficiently on milder days — the rating describes typical seasonal performance, not a constant figure.
• A newer SEER2 rating isn’t directly comparable to an older SEER number. The testing standard changed for equipment manufactured starting in 2023 to more accurately reflect real duct static pressure, producing somewhat lower numbers under the same real-world efficiency — check which rating standard your specific unit uses before comparing it to an older system’s SEER number.
• For a heat pump’s heating-season cost, use its HSPF rating instead of SEER. SEER measures cooling efficiency; a heat pump’s heating mode is rated separately using HSPF (Heating Seasonal Performance Factor). This calculator’s SEER-based formula applies to cooling operation only.

The Formula

$$\text{Power (kW)} = \frac{\text{BTU/hr}}{\text{SEER} \times 1,000}$$ $$\text{Cost} = \text{Power (kW)} \times \text{Hours per Day} \times \text{Days} \times \text{Electricity Rate}$$

Worked Example

A 24,000 BTU/hr (2-ton) air conditioner with a SEER 16 rating, running 6 hours a day for 90 days at $0.18 per kWh:

1. Power draw: $24,000 \div (16 \times 1,000) = 1.5$ kW.
2. Daily energy: $1.5 \times 6 = 9$ kWh.
3. Daily cost: $9 \times 0.18 = \$1.62$.
4. Total cost over 90 days: $\$1.62 \times 90 = \$145.80$.

Upgrading to a SEER 20 unit with the same output would cut that power draw — and the total cost — by 20%, all else being equal.

Common Mistakes

• Entering the thermostat’s “on” time instead of actual compressor runtime. A system cycles on and off to hold a set temperature rather than running the whole time it’s active — using the full “cooling season” hours instead of real runtime overstates the cost significantly.
• Comparing a SEER2 rating directly against an older SEER number. The two ratings use different testing standards and aren’t apples-to-apples — check which standard a given unit’s nameplate actually uses before comparing efficiency across systems.
• Using SEER for a heat pump’s heating-mode cost. SEER only measures cooling efficiency — a heat pump’s heating-season cost depends on its separate HSPF rating instead.
• Assuming SEER is a fixed, constant efficiency. It’s a seasonal average — real efficiency dips on the hottest days and improves on milder ones, so a single day’s actual cost can vary from the seasonal estimate.

Useful to Know

• Already know your system’s actual monthly kWh usage instead of its BTU/SEER specs? The Electricity Cost Calculator calculator starts from usage directly.
• Sizing a new air conditioner for a room rather than costing an existing one? The BTU / Air Conditioner Sizing Calculator calculator estimates the cooling capacity a space actually needs.
• Considering a heat pump instead of a standard AC unit? The Heat Pump Sizing Calculator calculator estimates the right capacity for your home.