Pipe Sleeves
If your condensation drain is PVC or copper and of traditional 1- or 1 1/2-inch size, commercial pipe sleeves are available at many hardware stores. They are typically gray and made of Styrofoam, which will serve to insulate the pipe from the hotter temperatures in the attic and prevent condensation accumulation and water damage.
Rubber Coating on Pipe
There are third-party products made of rubber, sold under the brand name Rubatex, that can be wrapped around condensation drainpipes to prevent sweating. They typically come in rolls similar to duct tape and should be wrapped around the pipe from the air handler to the point where the pipe exits the attic.
Drain Hole
Insulate the area surrounding the drain hole, where the condensation pipe exits the attic, using a few commercial products. Polystyrene expanding foam insulation products can be sprayed into the opening and allowed to expand to form an air- and water-tight seal. In a pinch, silicone caulking around the circumference of the pipe will work well to keep the elements out of the attic.
Condensation Drain Trap
In the condensation drainpipe there should be a small elbow, called a trap. This trap remains filled with water and prevents air from traveling from the outside of your home through the drainpipe and into your attic. Ensure this trap is properly installed and functioning properly to avoid not only air leaks but also potential condensation drain malfunction.