Direct vent: two-pipe layout and intake separation

What is going on

Direct vent. Two pipes. One brings combustion air in, one sends flue gas out. Exhaust has to sit at least 12 in above the intake on vertical runs, or flue gas gets pulled right back in. Keep the combustion air inlet at least 3 ft from any other gas or fuel-burning vent or clothes dryer vent, except for multiventing. Both pipes must end in the same atmospheric pressure zone. Mix those up and you get nuisance pressure switch trips and bad combustion.

Likely causes

• Intake too close to the exhaust, so flue gas recirculates
• Intake near a dryer vent or another appliance vent
• Intake and exhaust terminated in different pressure zones
• Pressure switch trips and poor combustion traced back to the termination

Check in this order

1. Make sure the exhaust outlet is at least 12 in above the intake on vertical runs
2. Keep the combustion air inlet at least 3 ft from any other fuel-burning vent or dryer vent, unless multiventing
3. Terminate intake and exhaust in the same pressure zone
4. Check both terminals are clear of snow, leaves and screens
5. Inspect for leaks at joints and support the pipes per the instructions

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