Daily heating degree days calculator

Compare the daily mean temperature with the chosen heating base; warmer days contribute zero.

Units

\mathrm{HDD}_{\text{day}} = \max\left(0,\ T_{\text{base}} - T_{\text{mean}}\right)

Calculator

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

Given

\mathrm{HDD}_{\text{day}} = \max\left(0,\ 65 - 48\right) = 17

Symbol	Meaning	Unit
$\mathrm{HDD}_{\text{day}}$	daily heating degree days	°F·day
$T_{\text{base}}$	selected heating base	°F
$T_{\text{mean}}$	daily mean outdoor temperature	°F

Symbol	Meaning	Unit
$\mathrm{HDD}_{\text{day}}$	daily heating degree days	K·day
$T_{\text{base}}$	selected heating base	°C
$T_{\text{mean}}$	daily mean outdoor temperature	°C

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