Venting Requirements, Vent Pipe Material

inches of free area. See Figure 9. For example, if the combined input rate of all appliances is less than or equal to 100,000 Btuh, each opening must have a free area of at least 100 square inches. If the combined input rate of all appli- ances is 120,000 Btuh, each opening must have a free area of at least 120 square inches.

Air Directly Through An Exterior Wall

If combustion air is provided directly through an exterior wall, the two openings must each have free area of at least one square inch per 4000 Btuh of total appliance input. (See Figure 10.)

Outdoor Air Through Vertical Openings or Ducts If combustion air is provided through vertical ducts or openings to attics or crawl spaces, the two openings must each have free area of at least one square inch per 4000 Btuh of total appliance input. Ducts must have cross-sec- tional areas at least as large as the free area of their respective openings to the furnace space. Attics or crawl spaces must communicate freely with the outdoors if they are the source of air for combustion and ventilation. (See Figures 11 and 12.)

Outdoor Air Through Horizontal

Openings or Ducts

If combustion air is taken from outdoors through horizontal ducts, the openings must each have free area of at least one square inch per 2000 Btuh of total appliance input. Ducts must have cross-sectional area at least as large as the free area of their respective openings to the furnace space. (See Figure 13.)

!CAUTION:

Do not supply combustion air from an attic space that is equipped with power ventilation or any other device that may produce a negative pressure.

VENTING REQUIREMENTS

This section specifies installation requirements for vent and "2-pipe" combustion air piping. For "one pipe" installations, install vent piping per this section and provide air for combustion and ventilation per the previous section. The capac- ity table provided in this section applies to the total of vent and combustion air piping for either type of installation.

NORDYNE condensing furnaces are classified as "Category IV" appliances, which require spe- cial venting materials and installation proce- dures. Category IV appliances operate with positive vent pressure and therefore require vent systems which are thoroughly sealed. They also produce combustion condensate, which is slightly acidic and can cause severe corrosion of ordinary venting materials. Furnace operation can be adversely affected by restrictive vent and combustion air piping. Therefore, vent and com- bustion air piping lengths must conform com- pletely to the requirements of Table 5.

The furnace must be vented to the outdoors. It must not be vented in common with any other appliance, even if that appliance is of the con- densing type. Common venting can result in severe corrosion of other appliances or their venting and can allow combustion gases to escape through such appliances or vents. Do not vent the furnace to a fireplace chimney or building chase.

!WARNING:

FURNACE MUST NOT BE COMMON VENTED WITH OTHER APPLIANCES.

Vent Pipe Material

Vent and combustion air pipe and fittings must be one of the following materials and must conform to the indicated ANSI/ASTM standards:

Material	Standard
Schedule 40 PVC	D1785
PVC-DWV	D2665
SDR-21*	D2241
& SDR-26*
ABS-DWV	D2661
Schedule 40 ABS	F628

Cement and primer must conform to ATSM Standard D2564 for PVC and Standard D2235 for ABS. When joining PVC piping to ABS, use PVC solvent cement. (See procedure specified in ASTM Standard D3138.)

Vent Pipe Length and Diameter

In order for the furnace to operate properly, the combustion air and vent piping must not be exces- sively restrictive. To ensure this use Table 5, which indicates the maximum allowable piping length for a furnace of specified input rate, when installed