H = 1.08 q (t2 - t1) η
where
η = heat-recover efficiency
q = quantity of airflow (cfm)
H = heat transferred (Btu/h)
1.08 = a constant for sensible heat equations
t2 = air temperature of outside air after the heat recovery unit (oF)
t1 = air temperature of the exhaust air before the heat recovery unit (oF)
H = 4.5 q (h2 - h1) η
where
h2 = air enthalpy of outside air after the heat recovery unit (Btu/lboF)
h1 = air enthalpy of the exhaust air before the heat recovery unit (Btu/lboF)
4.5 = a constant for total heat equations