Horizontal vent slope, support and freeze protection

What is going on

Installation rules for horizontal and external vent and combustion air piping.

Check in this order

1. Slope all horizontal pipe up from the furnace at least 1/4 inch per foot so condensate drains back to the furnace.
2. Support all horizontal runs at least every 4 feet. No sags or dips.
3. Keep the minimum vent pipe length at 5 feet.
4. Do not install any part of the air or vent pipe underground.
5. Immobilize pipes at roof, wall and other penetrations so they cannot disconnect.
6. For direct vent, make sure the vent and inlet pipes end in the same atmospheric pressure zone.
7. Insulate piping outside the structure and piping through unheated spaces to prevent freezing.
8. Where water can collect on horizontal runs, wrap the vent with self-regulating 3 watt or 6 watt UL listed heat tape, installed per the manufacturer.
9. Never cover heat tape with insulation. Insulation such as Armaflex or Rubatex can be used only if no heat tape is on the pipe.

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