3280.509—Criteria in absence of specific data.
In the absence of specific data, for purposes of heat-loss/gain calculation, the following criteria shall be used:
(a) Infiltration heat loss.
In the absence of measured infiltration heat loss data, the following formula shall be used to calculate heat loss due to infiltration and intermittently operated fans exhausting to the outdoors. The perimeter calculation shall be based on the dimensions of the pressure envelope.
Infiltration Heat-Loss=0.7 (T) (ft. of perimeter), BTU/hr.
where: T=70 minus the heating system capacity certification temperature stipulated in the Heating Certificate, in F.
| Wall | 15 percent of wall area less windows and doors. |
| Floor and Ceiling | 10 percent of the area. |
(c) Insulation compression.
Insulation compressed to less than nominal thickness shall have its nominal R-values reduced for that area which is compressed in accordance with the following graph:
Code of Federal Regulations
Code of Federal Regulations
152
When insulation is installed over the framing members the thermal performance of the insulation is reduced due to compression at the framing members. The Resistance value of the insulation between the framing members is reduced by 12.5 percent for framing members 16″ O.C., 8.5 percent for framing members 24″ O.C., and 4 percent for framing members 48″ O.C.
(d) Air supply ducts within floor cavity.
Air supply ducts located within a floor cavity shall be assumed to be heating or cooling the floor cavity to living space temperatures unless the duct is structurally isolated by the framing system or thermally insulated from the rest of the floor cavity with a thermal insulation at least equal to -R-4.
(e) Air supply ducts within ceiling cavity.
Where supply ducts are located in ceiling cavities, the influence of the duct on cavity temperatures shall be considered in calculating envelope heat loss or heat gain.
(f)
The supply duct loss (and/or heat gain where applicable—See § 3280.511) shall be calculated using the actual duct surface area and the actual thickness of insulation between the duct and outside of the manufactured home. If there is an air space of at least 1/2 inch between the duct and the insulation, heat loss/gain need not be calculated if the cavity in which the duct is located is assumed to be at living space temperature. The average temperature inside the supply duct, including ducts installed outside the manufactured home, shall be assumed to be 130 F for purposes of calculation of heat loss and 60 F for heat gain.
(g) Return air cavities.
Cavities used as return air plenums shall be considered to be at living space temperature.