I have a 1 story ranch home in Birmingham, Alabama for which I just had the roofing replaced. I had the old shingles removed and replaced with more asphalt shingles. Before installation, I had two whirligigs on the roof for ventilation. I had those removed and replaced with 42 feet "shingle over ridge ventilator". At the same time, they did replace some other piping on top of the house with similar piping. One of those pipes has air coming out of it, resulting in a steam-like exhaust in this cold weather. For almost every day since the project ended, we have noticed some water trickling down (on top of the shingles) from this particular pipe. Is this a problem? What is the cause? Thanks

Are the other pipes a furnace or hot water tank vent? If so, you could be getting more condensation because you have better attic venation. It could also be because they slipped in single wall pipe in place of double wall. Check you furnace and hot water heater and make sure condensate isn't making it back to them.

Are you saying that a small amount of water trickling down from the pipe on a regular basis is not a problem if condensation is not evident around the water heater or furnace?

No a little water on the roof isn't going to hurt. Now, if there is also water condensing inside a galvanized vent pipe, that is bad. Heating condensate tends to have nasty acids in it that will eventually eat through galvanized. Then you could have deadly combustion fumes leaking into the house. You need to look things over carefully, and if you aren't sure, have a HVAC pro look at it. If the pipes are white plastic, then they are designed to resist condensate.

If this is temporary and will only happen in the very coldest weather, you may not have much to worry about.