Section 3280.506 - Heat loss/heat gain(a) The manufactured home heat loss/heat gain shall be determined by methods outlined in §§ 3280.508 and 3280.509 . The Uo (Coefficient of heat transmission) value zone for which the manufactured home is acceptable and the lowest outdoor temperature to which the installed heating equipment will maintain a temperature of 70 F shall be certified as specified in § 3280.510 . The Uo value zone shall be determined from the map in figure 1 to this paragraph (a). Figure 1 to Paragraph (a)
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(b) The overall coefficient of heat transmission (Uo) of the manufactured home for the respective zones and an indoor design temperature of 70 F, including internal and external ducts, and excluding infiltration, ventilation, and condensation control, shall not exceed the Btu/(hr.) (sq. ft.) (F) of the manufactured home envelope are as tabulated in the table to this paragraph (b): Table 1 to Paragraph (b)
| Uo value zone | Maximum coefficient of heat transmission |
| 1 | 0.116 Btu/(hr.) (sq. ft.) (F). |
| 2 | 0.096 Btu/(hr.) (sq. ft.) (F). |
| 3 | 0.079 Btu/(hr.) (sq. ft.) (F). |
(c) To assure uniform heat transmission in manufactured homes, cavities in exterior walls, floors, and ceilings must be provided with thermal insulation. For insulation purposes, the fire separation wall between each single family attached manufactured home shall be considered an exterior wall (see subpart K of this part).(d) Manufactured homes designed for Uo Value Zone 3 shall be factory equipped with storm windows or insulating glass.58 FR 55009, Oct. 25, 1993; 59 FR 15113, Mar. 31, 1994; 86 FR 2521 , Jan. 12, 2021