Steven L. Smith, Bellingham, WA Home Inspector (King of the House)

During the course of doing home inspections at King of the House, I run into this one frequently. In an older home this condition is, almost always, present. In a new home, usually it is not an issue.

Regardless, it is one of these subtle guidelines about how things should be done that most homeowners are not aware of. In real life it is not a big concern, compared to the serious problems one can find at an inspection, but it should be noted.

Air-handling ducts, and that includes things like the ducts from the bath exhaust fans, the laundry exhaust fan, the dryer and the range hood, should have insulation (R4 or better) around the duct where the duct runs through unconditioned spaces such as crawl spaces and attics. (R8 or better is recommended for wrap on heating and cooling ducts.)

In a new house, often this is accomplished at all ducts by use of plastic covered flex duct, with appropriate insulation inside the jacket. But other times, the ducts are wrapped with fiberglass batt or blanket insulation.

Sometimes people ask why this is required at all. The answer is that it helps prevent condensation from forming inside the ducts by keeping cold air off the outside as warm air passes through the inside. One point here: Obviously this does not apply to runs of cheap accordion flex duct or improper ducting materials. Fact is, those types of ducts need more than insulation. They need to be replaced with proper ducting, smooth metal, and then the insulation should be installed.

Another word of caution, if you are a do-it-yourselfer, this information DOES NOT apply to runs of B-vents (gas furnaces, gas water heaters, gas fireplaces) or vents from oil-burning appliances or metal chimneys from a wood-burning device. Those ducts need to be uninsulated and they must have proper clearances from all combustibles including insulation. Another related problem is loose ducts -- where they were taped and the tape deteriorated. For information on the proper way to fasten ducting, click here.

Thanks for stopping by,

Steven L. Smith