HVAC-Talk: Heating, Air & Refrigeration Discussion

There is an exhaust pipe from the furnace that goes up and out of the ceiling. There are 2 holes in the pipe, below where the exhaust pipe connects to the straight pipe that goes up and out of the ceiling. I am wondering what these holes are for. I have a photo but I guess I can

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HVAC-Talk: Heating, Air & Refrigeration Discussion

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HVAC-Talk: Heating, Air & Refrigeration Discussion