The Inside Outside Guys: Duct Sealing – a not so radical idea

Ken Calverley and Chuck Breidenstein
Special to The Detroit News

The Guys have said for years the forced air heating systems in many homes are the “poor stepchild” of the mechanical systems. Homes are historically wired, then plumbed, then the duct work is installed and not always by design so much as accommodation; as in “how can we make this work?”

Furnace units themselves were often “sized” based on loose rules-of thumb that resulted in slightly over-sizing for the home. Over-sizing results in furnaces that “short-cycle”. That is they blast a lot of heat very quickly for short periods of time, then shut down only to repeat the cycle a short time later. This prematurely ages blower motors while ineffectively moving and conditioning air.

Properly sized furnaces take into consideration the actual shape of the house and rooms as well as square footage of exterior walls, cubic footage and glazing and even the insulation package.

A home's leaking duct work can affect your comfort.

Take a look in your basement at the duct work and imagine how air is supposed to flow through it. Look for 90 degree elbows that cause “air traffic jams” and reduce air flow. Look for runs that make air move sideways or even down before it can go up. Then look for seams between pieces of duct. Every seam is several lineal inches of potential air leak. Every seam and leak creates further friction on the flow and reduces proper flow to where we are directing it.

Also, you should know that duct leaks contribute to accumulation of stuff in the ducts. Because leaks alter air flow and create different pressures in the duct, things like dead skin cells, hair, pet dander, etc. will begin to accumulate at those spots – much like plaque in an artery.

Add to all of this another dynamic. We are conditioning the air in cubes. Every room in our house is a cube and the only way to efficiently condition air in a cube is to move a lot of dedicated air consistently, if not constantly, through the space. The only way to get dedicated volumes of air to those spaces is through well designed and sized and sealed duct supply and return air systems.

A new home today is required to have sealed ducts and the professional HVAC companies referred by the Guys all incorporate good design into the system to expedite air flow and reduced friction.

But what about all of you that live in homes with an upper floor or distant room you can’t heat in winter or cool in summer? What if your house isn’t new?

Should you purchase and install low voltage booster fans in specific ducts to increase air flow? We, and the industry, have tried that. But it is largely ineffective and can actually create issues such as when a booster fails. It may further impede air flow and you are not even aware of the failure.

A solution to this issue the Guys have found is from Amistee Air Duct Cleaning of Novi. The proprietary system it uses  is infused into the duct system under controlled pressure and the product “seeks” out the leaks using those varied pressures we talked of earlier. And it seals them. Permanently. Sealed ducts also tend to deliver cleaner air. Healthier air.

Here’s the really interesting thing about this process. When the technicians arrive on the job, they measure air volume at every supply register and compare it to what should be delivered. They've found many houses have cumulative duct leakage equal to a 3 foot by 4 foot window. Unbelievable!

Amistee can demonstrate and measure how those hard-to-condition spaces were not getting the air they should and after sealing the ducts they are. And that room or space you could never heat or cool? It now is as comfortable as the rest of the house. The  company also has a product for sealing the ducts in a slab-on-grade floor.

For more home improvement advice listen to the Inside Outside Guys every Saturday and Sunday on News/Talk 760, WJR AM, from 10 a.m. to noon, or contact us at with your questions.