General Question

SuperMouse's avatar

Why doesn't snow accumulate on manhole covers?

Asked by SuperMouse (30845points) February 13th, 2009

As I was driving through this morning’s snow storm, I noticed that the snow was piling up everywhere but on the manhole covers. Does anyone know why this is? Experienced snowbirds, please forgive me if the answer is obvious I am still new to the whole snow thing.

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10 Answers

dynamicduo's avatar

Manhole covers tend to be warmer because of the air from the sewer pipes also being warm. I assume sewer pipes are heated or at least insulated, because they can’t get cold enough to let their contents freeze, thus the heat would travel upwards as heat does, and cause the manhole cover to become warmer, thus melting any snow that lies on it.

EmpressPixie's avatar

I think heat rises up through the covers keeping them—nevermind, DynamicDuo’s got it covered.

steelmarket's avatar

@dyna has it. The covers are solid steel, which is a great conductor of heat.

Jeruba's avatar

You can also sometimes see steam rising around them.

BCarlyle's avatar

Also consider that a portion of the water that enters the sewer is warmer. i.e. the water from your hot shower, washing clothes or dishes.

Emdean1's avatar

because thats where all the BUMS sit to keep warm!

tb1570's avatar

because they’re warm.

90s_kid's avatar

haha…..Kind of…

snowberry's avatar

The temperature inside a cave is 55 F. A sewer is not unlike a cave in that respect. The air inside a sewer is just about always warmer than the ground, however I would not be surprised if sewers in extreme northern climates are dug deeper than other places (to help prevent freezing in the event of a cold snap.

kritiper's avatar

@BCarlyle Nailed this one.

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