septic system
Septic system odors can have many causes.  Some can be minor, others more serious.  In cold weather, the causes can vary.  Pinpointing the source of the smell is usually the first step.  Downdrafts from the vent pipe on the roof may cause odor, but would vary with weather conditions and wind and subside as the day warms.
There could be a problem with a frozen drainfield, blocked tank inlet or outlet, or other blocked pipes.   Backup may occur in the home if this is the case.  Check the lowest drain in the system first.  Call a professional right away if you suspect this is the problem.
Long, persistent odors and wet spots over the tank and drainfield could mean septic system failure.  Check for effluent outside and wet spots where the grass may be particularly lush.
Does it smell right near the house?   Broken pipes or leaky pipes could account for this.  Effluent could be leaking out of the pipe and running along the pipe trench rather than through the pipe itself.  Blocked pipes could also be the problem forcing the sewage back toward the home.
The best course of action is to call a professional right away.  All Clear Septic and Wastewater Services have 24 hour emergency services as well as trained septic professionals to evaluate the problem and make any necessary repairs, which could save money down the road and prevent septic failure.
Call them at 508-763-4431 or visit www.allclearseptic.com