Surface conductances and resistances for combined
free convection and radiation in air

From ASHRAE (1989), with permission

Conductances given in Btu/(hr·ft2·°F)
Resistances given in (hr·ft2·°F)/ Btu

Values for still air

Position of surface

Direction of heat flow

Surface emittance

Non-reflective

Reflective

e = 0.90

e = 0.20

e = 0.05

hi

R

hi

R

hi

R

Horizontal

Upward

1.63

0.61

0.91

1.10

0.76

1.32

Downward

1.08

0.92

0.37

2.70

0.22

4.55

Sloping at 45°

Upward

1.60

0.62

0.88

1.14

0.73

1.37

Downward

1.32

0.76

0.60

1.67

0.45

2.22

Vertical

Horizontal

1.46

0.68

0.74

1.35

0.59

1.70

 Values for moving air for non-reflective surface with e = 0.90

Position of surface

Direction of heat flow

hi

R

15 mi/h wind (for winter)

Any

6.00

0.17

7.5 mi/h wind (for summer)

Any

4.00

0.25

Notes for both tables: