We purchased a 1890's era house on the Front Range of Colorado a little less than 2 years ago. We have a problem with blistering paint on the north side of our house. When we removed the blistered paint it exposed the bare wood underneath. From all the info on the internet, this would suggest that we have moisture building up from inside. The problem is that we can't figure out where the moisture might be coming from. We did install a humidifier on the downstairs gas furnace last fall (because we have incredibly dry air) but that only humidifies the downstairs. Most of the blistering is occurring on the exterior of the second floor. And most of it is happening on the exterior wall of a walk-in closet. The closet has a heating vent but we shut it off last year to conserve energy. There is virtually no blistering on that wall in the area of the upstairs bathroom, however, where we would be more likely to expect it. The sofit extends quite a distance over the portion of the wall that is blistering and we cannot find any leaks in the gutters or the roof. We're stumped! Any ideas?