Exterior Vertical Eaves Exit - If the exhaust pipe on the back of your heater goes through a wall, up the outside of your house, and through an eave, the horizontal run must NOT be more than 24 inches long.
Also, if the total run exceeds 10 feet, then a 4-inch inside-diameter pellet vent pipe should be used instead of a 3-inch pipe. Remember, the termination cap must be 12 inches above the roof. And if high winds are prevalent, a high-wind cap should always be used to prevent down-draft or obstruction of the exhaust flow.
** This information is generalized for use on all Thelin Pellet Heaters. Refer to your models installation and operating manual for information specific to your model.