This is a prolific question and one that sometimes breeds controversy. In the winter especially in northern climates, heat and humidity rise into the attic and when they meet the cold air, which is supposed to be in the attic, one thing always occurs…condensation. Condensation starts several events none of which are desirable. The attic insulation becomes laden with moisture which is heavy and causes the insulation to compress and settle over time, making it less effective. The insulation, when its “damp”, causes your furnace to work harder. In the winter, when there is generally less convection or circulation in the attic, moisture tends to build-up giving mold, mildew and fungus an opportunity to start. All of these plus the advantage of inhibiting ice dams (keeping the attic cold verses letting warm air rise in the attic, melting the snow cover near the ridge only to re-freeze further down the roof forming the classic ice dam) are reasons the SunRise Solar Fan benefits you year around.