Dirty Little Secrets About Your Home’s Ductwork

By Trish Holder

The duct installation my home is crap. But here’s the really bad news.  The duct installation in your home is probably crap too, especially if your home is relatively new.

“But that can’t be!” you say.  “I live in an upper-middleclass neighborhood named after a California wine vineyard!”

I’m so sorry.  Your duct installation is still probably crap, especially if it is relatively new.

How do I know?  Because crappy duct installations are pretty much the industry norm and most homeowners wouldn’t know a bad one if it cameto life and smothered them like a giant anaconda.

It’s not your fault.  Afterall, how many builders have a heart-to-heart with prospective buyers about what makes for a long lasting duct installation that resists wear and tear….has minimal turns and kinks….uses a sheet metal trunk line instead of continuously long runs of flex duct….and is well supported and carefully placed so as to minimize the risk for moisture and hence mold and mildew?

Lets face it.  It’s a lot easier and more effective to sell a homeowner on a luxurious, Italian tiled master bath with a shower that has 14 showerheads all strategically placed to take you to new heights in bathing ecstasy.  It’s hard to sell a pristine duct installation, no matter how much time, money, and heartache it saves in the long run.  Typically, the only homeowner who cares about such things is the one who has spent a fortune redoing their duct because of the mold and mildew that erupted due toexcess condensation collecting in or on ducts and  dripping on floors, ceilings, and in between walls, making their family sick along the way.

I was talking ductwork with my HVAC contractor just the other day.  He was at my house for some minor maintenance.  A damper motor needed replacing.  No biggie.  But while he was there, we started chatting about residential HVAC and all of the associated horror stories.  He told me that in the small community where he lives, he can literally go into a home, look at the HVAC system and associated duct runs, and know exactly who did the installation.  He mentioned one old-timer, probably long since retired or passed on, whose duct systems were built entirely of sheet metal (square, not round, and not one bit of flex).  They were a work of art, he said, a relic of days gone by.  These are duct systems that will outlast generations of homeowners.  He said that he and his men would stand around in awe and think about the time it must have taken to fabricate each and every section.

“Wow,” I said. “My duct is crap isn’t it?”

He shrugged.  He’s a good guy – doesn’t like to badmouth another contractor’s work.

“My duct is crap, isn’t it?” I persisted.


He went on to say that my duct is really no different than most duct systems he sees in new homes today, even great big mansion homes where flex duct is strewn about like silly string.

I felt a little better…. and a little worse.

Properly Sizing Duct
There’s something else people should know about duct systems.  Prior to installing a one a contractor should complete what is known as a Manual D load calculation.   These calculations are dependent on room-by-room heat loss and heat gain calculations arrived at when the contractor also performs what is known as a Manual J.  Manual J and Manual D calculations assure that the duct and HVAC unit is sized properly.  These calculations are actually required by most building codes, even though there is little enforcement.  If you don’t believe me, ask your builder what a Manual D or Manual J is and you will likely get a blank stare.  Many builders have never heard of such thing.

Assuming it’s not too late for you, or you are actually considering a complete HVAC renovation, I recommend reading this article by Martin Holladay of Greenbuildingadvisor.com:  Musings of an Energy Nerd.  You’ll be in a much better position to approve and oversee any workmanship that involves your home’s air delivery system.  And your builder or contractor will realize right away that you are no ductwork dummy.

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