sat, 13-dec-2008, 16:43

Heat gun, vent pipe

Heat gun, vent pipe

Last winter our vent pipe froze solid and I spent a couple hours in the attic with a heat gun melting the blockage. A couple days ago I noticed that flushing the toilet was pulling water out of the traps in the sink and bathtub, so I knew the vent was getting plugged again. My attempt at a fix over the summer was to put a larger pipe over the vent on the roof so the condensation might happen in the outer pipe, which could be easily removed and cleaned out. Unfortunately, when I got up on the roof today, not only was it impossible to get the outer pipe free, but the growing constriction wasn’t in the outer pipe anyway. Mid-summer my neighbor suggested replacing the section of the vent in the attic with a much larger diameter pipe (6” was his suggestion) and then insulating it. I never got around to it; almost frozen vent pipe; a priori.

The total freezing degree days to this point in the winter season has been 2,258, which ought to give me a pretty good way of estimating when I’ll have another problem. Thus far we’ve had 74 days with an average daily temperature below freezing, and the average temperature for those days was 1.4°F. That’s below normal for the year: nine of the last eleven weeks have been below average. But the heart of the winter is approaching, so it’ll take many fewer than 74 days to double our freezing degree days for the season.

My first attempt to fix the clog was to insert a heat gun into the clean out and let the warm air from the heat gun melt it (shown in the photo). I don’t think this had any real effect. I kept it going for a little over an hour, monitoring the backside of the pipe to make sure the heat gun wasn’t melting it. But it was around -10°F this morning, so I’ll bet the hot air was pretty cold by the time it rose to the ice. The second attempt was using a pipe snake from up on the roof, but it couldn’t go past the constriction, and even if it had, I’m not sure it really would have cleared out much ice. Finally, I dragged a five gallon bucket filled with hot water up onto the roof. I got about three gallons into the vent before it was filled to the top. At first I was nervous that this wasn’t going to work and I’d have three gallons of water turning to ice in the vent, but the water started dropping slowly, and after a minute, the blockage gave way and hot water came plunging down the pipe. I poured the final gallon or two through the pipe, and came down off the roof.

Tomorrow I’ll put some 2” fiberglass insulation around the part of the pipe that’s exposed in the attic, which should help. And I’ll be keeping my eye on the total freezing degree days for the rest of the winter. Once it gets up to 4,000, I may want to go back up on the roof with another bucket of hot water.

SQL query from my weather database: SELECT sum(32.0 - t_avg::double precision) FROM daily;
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