MountainGirl, the staff at A&M Biofilters suggests the following:
“By extending the vent up in the air you are only sending the gases higher in the air.”
Well, if the gasses are sent higher in the air, then they are higher than your nose, unless you are having a problem with constant or occasional down drafts. I received a report from a person with the same problem that had installed an Odorhog on his roof vent. The location for this installation was in Wisconsin, or maybe Minnesota, where it has been unusually cold this winter. Well, the activated carbon filter worked perfectly for a while, but then the formation of hoarfrost within the housing of the filter restricted the venting capacity of the system, and then caused drainage problems and sewer gas odors inside the home.
I have been concerned about this potential, as I have recommended the use of activated carbon filters in the past to solve this problem. I have installed several activated carbon filters on roof vents of my septic system clients who experienced sewer gas odors emanating from the roof vents. Every one of these filters solved the problem and none of those installations developed the hoarfrost problem, several of which were in the very cold high country of Colorado.
So, based upon my experiences, I would try extending the vent pipes first. If you still have the odor problem, then try the activated carbon filter approach. If hoarfrost develops in the filter unit, then perhaps wrapping a small heat tape around the vent pipe just below the roof of the house will generate enough heat to keep the activated carbon free of hoarfrost.
John Aldrich (Septic Tank Yank)
Septic System Consultant