Avoided exhaust heating cost calculator

Exhaust reduction saves replacement-air heating in addition to motor electricity.

Units

S_{h} = \frac{\dot{V} \times 60 \times {\Delta h_{\text{day}}} \times \text{days}_{\text{heat}} \times \rho \times c_{p} \times \Delta T \times c_{f}}{\eta_{h}}

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

Given

S_{h} = \frac{6500 \times 60 \times 2.4 \times 135 \times 0.075 \times 0.24 \times 31 \times 0.000015}{0.82} \approx 1{,}290

Symbol	Meaning	Unit
$S_{h}$	annual heating savings	$/yr
$\dot{V}$	avoided equivalent exhaust airflow	ft³/min
${\Delta h_{\text{day}}}$	daily exhaust hours avoided	h/day
$\text{days}_{\text{heat}}$	annual heating days	day/yr
$\rho$	air density	lb/ft³
$c_{p}$	air specific heat	Btu/(lb·°F)
$\Delta T$	indoor-outdoor temperature difference	°F
$c_{f}$	fuel price	$/Btu
$\eta_{h}$	heater efficiency	fraction

Symbol	Meaning	Unit
$S_{h}$	annual heating savings	$/yr
$\dot{V}$	avoided equivalent exhaust airflow	L/s
${\Delta h_{\text{day}}}$	daily exhaust hours avoided	h/day
$\text{days}_{\text{heat}}$	annual heating days	day/yr
$\rho$	air density	kg/m³
$c_{p}$	air specific heat	kJ/(kg·K)
$\Delta T$	indoor-outdoor temperature difference	K
$c_{f}$	fuel-energy price per kilowatt-hour	$/kWh
$\eta_{h}$	heater efficiency	fraction

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.