Dirty Little Secrets About Your Home’s Ductwork

Duct installationBy 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.

“But how can that 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 came to 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 ultimately saves.  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 to excess 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 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.

9 Responses »

  1. Trish,

    A major leap forward in de-crapifying ductwork is to move the ductwork out of the attic and into conditioned space. Think about it….attics can get over 100 degrees in the summer and duct insulation is only R-6 or so. That means that in order to blow cool air, the system must first spit out the old hot air. To make matters worse, HVAC contractors like to hang their ductwork from the highest positions in the attics, a.k.a. the hottest positions, like a huge octopus Duct tape and plastic straps don’t last in this type of environment. Your ductwork is at least laying on the joists; too bad they’re not covered in insulation. The question is did your contractor ensure that the ducts were not crimped where they connected to the boot on the attic side of the register.

    If the ductwork was in conditioned space, even if it leaked, it would leak in areas that were supposed to be heated or cooled anyway.

  2. Trish, “the ‘heart’ of any HVAC system is the space conditioning unit itself.” Much attention, time and effort have been given to the “heart” by the equipment manufacturers, e.g. vastly improved cooling efficiencies (SEER) and heating performance (HSPF and AFUE), environmentally-friendly refrigerants and multi-speed fans and compressors. But, alas, for decades the importance of the design, installation, and performance of the “veins and arteries”, the HVAC duct system, has essentially been ignored. Specifically, architects generally leave no room for the unsightly ductwork, owners recoil in disdain if “furr-ins” are mentioned, plumbers must have their space since it is a given that waste must have its path to leave the structure, etc. Most HVAC contractors will agree with this statement from the building contractor: “The other subs must have their spaces. You boys run your ducts wherever you can.”

    It is interesting to note, however, the moment the new owner turns the HVAC unit on and there are hot and cold spots throughout the structure, the finger of blame goes directly to the HVAC contractor. Poorly-designed and installed HVAC duct systems can account for more than a 60% reduction in total system efficiency, occupant comfort and energy usage. While numerous approaches to duct design have been presented in textbooks and manuals, we have a design method that has resulted in thousands of comfortable, quiet buildings with low energy bills.

    Even experienced HVAC contractors can run into problems by attempting to design their own systems. Many HVAC contractors have ignored our (brand name withheld) engineered layouts and relied on his “thirty years of experience” to design a job. These poorly designed systems are clearly insufficient for optimal performance, energy efficiency, consistent air flow and humidity control. In many cases, poor performance results in a total system replacement at considerable expense and inconvenience. (Brand name withheld) engineered duct systems are up to 60% more efficient than a typical radial “spider flex” duct installation:

    Proper duct designs and precisely engineered system sizing ensure optimal performance and humidity control. Call backs are virtually eliminated. Customer satisfaction is “GUARANTEED.” Why everyone is not installing extended plenums is insane.

    • Today’s HVAC contractors are not designing and installing galvanized trunk systems for a number of reasons:
      1) There are too many untrained and incapable HVAC contractors doing business.
      2) It’s easy (and sometimes profitable) to run 35+ft. of flex with kinks and leaks.
      3) The builder wants the lowest price (and the lowest priced contractor).
      4) It takes time to do a room by room load calc and then install the system in a professional
      5) Building officials are not enforcing the building codes (No load calc—No Permit)
      We design and build all our duct systems from prime galvanized stock with radiused fittings, turning vanes etc. I design my supply trunk at .05 SP and my return trunk at .04SP. Proper airflow is all about CFM, FPM velocity and system static pressure. There’s a lot of science involved and the lowball HVAC contractor has no time for this. There’s quick money to be made. This will not stop until consumers stop buying homes with crappy duct systems.

  3. Hi Trish,

    I agree with the previous 3 responses. Homeowners need to get involved, educated, and concerned with the most important “system” in their home. It seems that comfort systems, are an out of sight, out of mind item in the home. They are not beautiful, they do not make your friends jealous, they do not increase your status in society, and they do not make homeowners pound their chest, grunt, and shout with glee.

    Ducts are a major part of the home comfort system. What comfort systems will do, especially when they have improperly designed, sized, and installed, ducts, is make or break whether or not you love your home. They affect the health, safety, efficiency, cleanliness, and comfort of your home, and most importantly, they affect the health, safety, efficiency, comfort and BANK ACCOUNT of your FAMILY!!

    There is a simple solution. After a properly designed and sized system is complete, have a certified air balancing company, a third party, test the system for proper airflow, heating BTU and cooling BTU delivered to each room. Do not accept, or pay for, more than 50% of the installed work until this testing is complete, and at least 90% of the total system capacity is actually getting to where its supposed to in the conditioned area of the home.

    Think of it like this:
    What would you do if you just bought a new car slated for 50 MPG, drove it for a month, and realized you are only getting 12 MPG?
    Unfortunately when it comes to home comfort systems, this scenario is happening to utility bills in millions of homes every day, and consumers are as much to blame as the contractor. They accept it!!

    It is time for America to wake up and start demanding for proof that they are getting what they are thinking they are paying for. Testing the system is the solution.

    Just don’t get me started on maintenance.

    Keep up the good work!

    Joe Gorman
    Certified Air Balancer, Certified Combustion and Carbon Monoxide Analyst, HVAC Contractor
    “From Contractor to Consumer, the Truth about Heating, Air Conditioning, and Home Comfort Systems”

  4. Maybe just maybe it should be “Code”, I know, not another code. I see stuff like this all the time, I have it in my own home, which was flipped.

    We use it in class on the subject of not what to do!

    I like Joe’s comment. Have the house commissioned if it’s new, by a commissioning agent. Sit down during the design stages, with all vendors, home owners, arch, etc., a design charrett. If buying an existing new home, have a blower door, at builders expence, tested on energy efficiencies and air tightness.

    Suggest that the builder write a new home maintenance operations manual, a how to on how to operate your home.

    Robert Haverlock
    Certified Sustainable Building Advisor

  5. you should give a lot of thought to ducts its better to get metal ducts vs the plastic flexible that out gas and have uv and hepa filters. but I would consider a ductless split system and get rid of them all together uses less energy.

  6. Unsightly duct work is a problem for many yrs. Five yrs ago, when we built our now office, I insisted that we use pre-engineered floor joists between the main and upper level. I told the floor joist designer to make sure he identified 2 spaces in the design that would accommodate sheet metal trunk lines. The flex line is then acceptable to run from trunk line out to the vents for both main level and loft level vents.
    Works great!!

    I convinced my son to do the same thing for his home he built 3 yrs ago, he did, but the HVAC guy had no idea how to work with this space, and still made a mess of the system.

    These systems need to be discussed during the design of the home, and the HVAC guy needs to have his input.
    If I ask an HVAC guy to bid my houses with sheet metal main trunk lines, and he says “How am I going to work with that”, I know to move on to another HVAC shop.
    There are still plenty of good HVAC shops around that will do a great job, and do it right.

    If you are simply looking at the cheapest guy on the block, you are not going to get the best job done.

  7. I’ve worked around all facets new construction all of my life and the HVAC contractors I’ve been associated with seem to want you to believe that they wave a magic wand and cool air comes out of the ducts! They want to charge $50 an hour-$75 if you watch and $100 if you help; they want you out of the picture!
    After LEEDS, HERS, multiple BPIs and everything else the government could throw at us, I monitored work done by the Weatherization Program for two years. If I was on the job and watched, the contractors did exactly what they were supposed to. If I picked random jobs and visited after the work was complete…well, you can draw your own conclusions.
    I had many conversations with these contractors about exactly what they knew about duct construction and most knew exactly what to do, it just wasn’t affordable. As long as there are ways to cut corners, corners will be cut. Homeowner education is key here. The analogy of the Italian Marble shower is spot on…most of the money is spent on what others can see!

    • I agree that homeowner education is key. I think any contractor that encounters a customer that seems to have at least a basic understanding of how a job should be handled is likely to be more on their game — just because they know they aren’t dealing with someone who is completely ignorant about the work that is being done. That said, it is up to the homeowner to be clear about what their expectations are and accept that doing the job correctly takes more time (therefore costs more money). In the end, both the homeowner and the contractor win.

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