Sizing Guide

ManualsBrandsHart & Cooley ManualsPlumbing Supplies6" x 18" B Round Gas Vent Pipe (6RP18)

a. 1 inch

/3000 Btu/hour of the total input rating of all

equipment located in the enclosure, and

b. Not less than the sum of the areas of all vent connectors

in the confined space.

A combination of air supplied from both the indoors

and outdoors is also permitted. See NFPA 54 for these

provisions.

Local Building Code

Should the local building code differ from

recommendations given in this Guide, consult with

your building inspector or other local administrative

authority. As stated in the Foreword, the information

given is based on the latest scientific data, which has

been further verified by a long and satisfactory use

history. These data and practices given herein will

invariably provide better results than practices

required by an obsolete code.

Correction for Altitude

The vent system should always be designed for the sea

level nameplate rating (greatest input when unit has

modulated input) of the appliance, regardless of the actual

derated operating input required by the local altitude.

Outside Vents

The gas vent sizing tables are not applicable to outside

(exposed) chimneys or vents below the roofline per

NFPA 54. A Type B vent lining an exposed masonry

chimney is considered to be an enclosed vent system,

and these tables may be used.

Connectors

Single-wall pipe (stovepipe) is not recommended for use

in TYPE B venting systems. Because of the higher heat

loss from the flue products, the draft is reduced and

condensation can occur. The resulting moisture may

corrode the pipe and will likely leak out on the building

and contents, causing damage.

Where single-wall connector pipe usage is accepted local

practice, the following considerations must be followed:

1. Minimum clearance to combustibles is 6 inches

instead of the 1 inch required for Hart & Cooley

vent.

2. The heat loss is roughly double that for B-Vent, so DO

NOT USE IN ANY COLD OR CONCEALED SPACES,

AS CONDENSATION WILL RESULT AND LEAD TO

VENTING FAILURE AND POSSIBLE OTHER DAMAGE.

Connector Rise

The immediate vertical height from the flue collar to the

first turn (connector rise) will have an important effect on

the proper functioning of a venting system. In order for a

venting system to prime (for flow up the vent to start),

the vent MUST be heated by the flue gases. If it is

easier (less resistance) for the flue products to spill out

the draft hood relief opening than to flow into the vent,

priming can be delayed or prevented altogether. By

using all of the vertical height (head room) available

(NEVER less than 1 foot), a venting system will usually

prime within 8 to 10 seconds. Small increases in

connector rise generally have a greater impact on vent

capacity than an increase in common vent height.

Vent Cap or Termination

Use only Hart & Cooley

companion listed caps or

roof assemblies. The capacity and wind resistance

depends on the correct termination. Terminations on

any factory-built chimney housing or other custom

enclosure or chase MUST comply with the instructions

for a roof surface.

Appliance Type Limitations

Appliances that are NOT to be connected to TYPE B

gas vents:

• Gas Incinerators—Use the Hart & Cooley

Model TLC

Chimney. This is treated as a solid fuel-burning

appliance.

• Gas Clothes Dryers—These produce positive pressure

discharge and will cause backflow to the other

connected appliances. They will also discharge lint,

which may eventually block the discharge.

• Power Burners—Not classified as Category I or with

positive draft, and are NOT allowed on TYPE B venting

systems.

• All Condensing Type—Category IV (High Efficiency)

Appliances—are NOT ALLOWED on TYPE B venting

systems. Condensation will leak out and damage the

structure and contents.

Table Limitations

The Tables in Section 1 of this Guide include the

following considerations:

• Low resistance Hart & Cooley

RC, RHW or RM cap

• Listed Category I appliances

• Two 90° turns except for “0” lateral

For each additional 90° elbow or equivalent beyond two,

reduce the tabled capacity by 10%.

The vent connector should be routed to the vent,

utilizing the shortest possible route.

• Chimneys and vents on an outside wall must be

enclosed below the roofline.

*See page 8 for definitions of gas appliance categories.

Pipe Diameter 3" 4" 5" 6" 7" 8" 10" 12" 14" 16" 18"

Pipe Area sq. in. 7.1 12.5 19.6 28.3 38.5 50.3 78.5 113.1 154 201.1 254.5