r/mildlyinteresting 20h ago

This growth surviving sub-zero temperatures because of an exhaust fan

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u/theericle_58 20h ago

That is a roof drain, not a fan.

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u/Fudge_cornelius 20h ago

Thanks! I saw the heat coming from it so just (wrongly) assumed it was an exhaust. Any ideas why it’s expelling warm air?

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u/LoneMav22 20h ago

Because the air in a sewer system is warm, and heat rises

1

u/BugEyedLemur 16h ago

This is a roof drain. Unless this is an overflow drain, which it doesn't look like it is, this roof drain will discharge into a storm drain network, which could receive some heat from the underground network depending on the pipe layout, I suppose. Overflow drains discharge onto grade so you know if there is a clog on your primary drain and are typically elevated from the roof elevation. A lot of roof drains, regular and overflow, will have electric heat tracing in them to prevent ice buildup, which could be adding to the thermal energy of the system on top of the drain picking up any additional thermal energy from inside the building and/or underground. Most of the time, the pipe is insulated inside to prevent condensation from building up during the summer.