I live in Minnesota and my sewer vent on my roof will frost over when it gets really cold out, sending sewer odor in my house. Do you know if there is anything to do to keep it from frosting over?

Heat tape

I live in Canada and had a simliar problem, I learned a trick from a local plummer. If you bring the pipe up to the prescribed height and then put 2 90 degree fittings on (so it looks like an upside down J) no snow can get in the pipe and any moisture from melted snow etc will fall out, rather than gathering on the rim of the pipe and freezing, last year I had an actual ice plug in the pipe from similar problem, but the above solved it.

Do this: Buy cheap electric blanket. Wrap it around the pipe in the attic. Make sure entire exposed vent pipe is nicely wrapped. Tape it over with duct tape so blanket won't slip down. Blanket should cover this vent all the way under the roof. Plug cord into timer, set time of operation and turn it ON. The blanket will keep the pipe worm and will prevent ice from accumulating inside the pipe. That will do...

put 2 90 degree fittings on (so it looks like an upside down J) A more simple solution would be to install vent caps, (See image) on your vents. Good luck and stay warm. Tom