This paper presents the results of a project aimed at providing guidelines for venting condensing and near-condensing type gas-fired appliances. Current vent data appearing in the ASHRAE Handbook for noncondensing systems are not applicable. The guidelines were prepared using a computer model (VENT) that calculates the capacity of vent systems. The model can calculate capacities for the following range of appliance conditions:

Inputs: 10,000 to 10 million Btu/hr, (2.931 to 2.931 103 Kw)
Vent diameters: 1.5 to 12 in. diameter, (3.81 to 30.48 cm)
Height: 0 to 100 ft, (0 to 30.48 m)
Horizontal distances: 0 to 100 ft, (0 to 30.48 m)
Vent pressures: -0.5 to 10.0 in w.c., (-1.25' 102 to 2.49' 2.49' 103 Pa)
Vent gas temperatures: 100, 200, and 300°F, (37.8, 93.3, and 148.9°C).

The vent capacity data provide a technical base for the development of American National Standards Institute (ANSI) standards for high efficiency appliances. The information will supplement data already in the ASHRAE Handbook covering the venting of noncondensing appliances.

This paper also presents guidelines covering condensate handling, materials of construction, and other vent system considerations required of this category of gas appliances.