5
RECOMMENDED RELATIVE HUMIDITY
BY OUTDOOR TEMPERATURE
* Indoor relative humidity level when outdoor air is heated to 72°F.
† As stipulated by the Air Conditioning Contractors of America.
MAXIMUM MOISTURE REQUIREMENTS
*
* Based on design conditions of outdoor 20°F dry bulb, 80% RH; indoor 70°F dry bulb, 40% RH, and
minimum moisture production from residential operations for an absolute humidity difference of 0.0049
lb/hr.
NOTE:
Tight house is defined as being well insulated, having vapor barriers, tight storm doors and
windows with weatherstripping, and having dampered fireplaces.
Average house is defined as being insulated, having vapor barriers, loose storm doors and
windows, and having dampered fireplaces.
OUTDOOR
TEMP
(°F)
OUTDOOR
RELATIVE
HUMIDITY
(%)
INDOOR RELATIVE
HUMIDITY (%)
W/O HUMIDIFIER*
MAXIMUM
RECOMMENDED
INDOOR
RELATIVE
HUMIDITY†
–10
30 to 70 1 to 2 20 (Lo)
0
30 to 70 2 to 4 25
10
30 to 70 3 to 6 30
20
30 to 70 4 to 10 35
30
30 to 70 6 to 15 40 (Med)
VOLUME OF
RESIDENCE
(CU FT)
TIGHT
HOUSE
AVERAGE
HOUSE
Pounds
Per Hour
Gallons
Per Day
Pounds
Per Hour
Gallons
Per Day
8,000
1.76 5.09 3.52 10.17
10,000
2.21 6.35 4.41 12.72
12,000
2.64 7.63 5.29 15.26
14,000
3.09 8.91 5.92 17.08
16,000
3.53 10.18 7.06 20.35
18,000
3.97 11.45 7.94 22.89
20,000
4.41 12.72 8.82 25.44
22,000
4.85 13.99 9.71 27.98
24,000
5.29 15.27 10.59 30.52
26,000
5.74 16.54 11.47 33.07
28,000
6.18 17.81 12.35 35.61
30,000
6.62 19.08 13.24 38.16
INDOOR RELATIVE HUMIDITY LIMIT
FOR NO WINDOW CONDENSATION
(Indoor Air at 74°F Dry Bulb
)
OUTDOOR
TEMPERATURE (°F)
SINGLE
PANE WINDOWS (%)
DOUBLE
PANE WINDOWS (%)
40
39 59
30
29 50
20
21 43
10
15 36
0
10 30
–10
726
–20
521
–30
317
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