Could you be a little more specific because those values vary. What type of an intake (for an appliance, for home ventilation, etc.) and what type of an exhaust (high efficiency furnace regular furnace, power vented water heater, etc).
For a high efficiency furnace roof exhaust / intake termination you can check the drawing at this link - high efficiency furnace venting
For the power vent water heater exhaust pipe termination check this post: water heater PVC vent pipe
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