What is the maximum horizontal length for a 6-inch diameter vent when installed with a 20-foot vertical run?

What is the maximum horizontal length for a 6-inch diameter vent when installed with a 20-foot vertical run?

• A. 5'
• B. 10'
• C. 20'
• D. 15'

Answer: (D)

Vent lengths are limited to keep the draft from being too weak and to prevent backdraft or condensate buildup. For a given vent diameter, the allowable horizontal run depends on how tall the vertical rise is. With a 6-inch diameter vent and a 20-foot vertical rise, the standard venting table sets the maximum horizontal segment at 15 feet. That 15-foot limit keeps the pressure drop and resistance within what the appliance and vent system can handle to maintain a reliable draft. So, 15 feet is the longest horizontal run allowed under these conditions. Shorter horizontals, like 5 or 10 feet, would also be acceptable but aren’t the maximum. A 20-foot horizontal would exceed the limit and could compromise venting performance.

Vent lengths are limited to keep the draft from being too weak and to prevent backdraft or condensate buildup. For a given vent diameter, the allowable horizontal run depends on how tall the vertical rise is. With a 6-inch diameter vent and a 20-foot vertical rise, the standard venting table sets the maximum horizontal segment at 15 feet. That 15-foot limit keeps the pressure drop and resistance within what the appliance and vent system can handle to maintain a reliable draft.

So, 15 feet is the longest horizontal run allowed under these conditions. Shorter horizontals, like 5 or 10 feet, would also be acceptable but aren’t the maximum. A 20-foot horizontal would exceed the limit and could compromise venting performance.