Spot Exhaust Energy Cost Calculator
Annual conditioned-air cost of a spot exhaust fan.
Enter your values
ⓘ Live results
- Annual makeup-air heating cost
- $140
- Annual fan electrical cost
- $4
- Total annual cost
- $144
- Note
- Cooling-season costs would use similar math with the AC system's efficiency
Quick answer
The energy cost of a spot exhaust fan is driven mainly by the conditioned makeup air it pulls in, not the fan's own small electrical draw.
Cost = CFM x 1.08 x deltaT x hours/yr / heating efficiency x fuel cost, plus fan electrical cost
How to use the Spot Exhaust Energy Cost Calculator
- 1Enter the fan's exhaust airflow and daily runtime.
- 2Enter the typical indoor-outdoor temperature difference during operation.
- 3Enter energy cost and fan wattage to see conditioned makeup air cost versus the fan's own electricity use.
Worked example
Using the values the calculator loads with:
Inputs
- Exhaust airflow150 CFM
- Runtime3 hours/day
- Avg indoor-outdoor temp diff30 °F
- Heating cost0.09 $/kWh equiv
- Fan power draw40 W
Results
- Annual makeup-air heating cost$140
- Annual fan electrical cost$4
- Total annual cost$144
- NoteCooling-season costs would use similar math with the AC system's efficiency
Frequently asked questions
Why is makeup air cost so much bigger than fan electricity?
A small fan draws very little power, but the heated or cooled air it exhausts must be replaced by outside air that needs conditioning.
How can I reduce this cost?
Use timers/occupancy sensors so exhaust fans run only as long as needed, and consider heat-recovery ventilation for continuously-running exhaust.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.