### Sensible Heat-Recovery Systems formula

*H = 1.08 q (t*_{2} - t_{1})* * *η*

*where*

*η** = heat-recover efficiency*

*q =** quantity of airflow (cfm)*

*H =** heat transferred (Btu/h) *

*1.08 = a constant for sensible heat equations*

*t*_{2}* = air temperature of outside air ***after** the heat recovery unit (^{o}F)

*t*_{1}* = air temperature of the exhaust air ***before** the heat recovery unit (^{o}F)

### Total Enthalpy Heat Recovery System formula

*H = 4.5 q (h*_{2} - h_{1})* * *η*

*where*

*h*_{2}* = air enthalpy of outside air ***after** the heat recovery unit (Btu/lbºF)

*h*_{1}* = air enthalpy of the exhaust air ***before** the heat recovery unit (Btu/lbºF)

*4.5** = a constant for total heat equations*