“Seriously. I want you to hear this. It’s not your fault.”
In a couple of month’s time, many HVAC contractors across Georgia will be hearing these words from their therapists…and the therapists will be correct. It’s really not the HVAC contractors’ fault.
The issue that will have these contractors flocking to therapy is the enforcement (beginning 1 July) of the duct tightness requirements adopted this year by the state of Georgia. Along with the building envelope leakage (infiltration) requirement of less than 7 ACH50 (7 air changes per hour measured at 50 Pascals), all new homes are required to have duct leakage* less than 8 CFM25 (cubic feet per minute measured at 25 Pascals) per 100 square feet of conditioned floor area (often referred to as 8%, although it’s not a true percentage).
I’ve had the opportunity to spend the last few months working with a couple of proactive builders in the metro Atlanta area that want to ensure they can meet the new tightness requirements once enforced. The glaring conclusion from these tests is the duct leakage requirement is going to give builders fits if they don’t develop a remedy for it. Most builders will achieve the envelope tightness without much problem. Don’t get me wrong, I’m excited that Georgia’s code is making the industry measure it, but it’s not that big of a challenge for builders to hit 7 ACH50.
The duct leakage is where the real problems are. For the most part, the ductwork and units are pretty well sealed. There are often small holes in the cabinet that could be sealed better and the filter doors continue to be a disaster (aside from the 4” media filters), but these are small potatoes. The big issue is at the boots. Practically no sealing takes place here at the present, and it’s easily the largest source of duct leakage in a new home. It’s also not just a single issue at the boots, it’s two specific locations: between the boot and the metal frame and more importantly, between the ceiling drywall (or subfloor) and the metal frame.
Why this is not the HVAC contractors fault is the timing of construction activities. The time to perform this sealing usually doesn’t align with their typical site visits. Should it be the painters? Drywallers? Insulators? Site supervisors? Punch out specialists? I think the answers will vary, and it will be up to the individual builders to decide when this sealing should take place given their particular build process.
In no way am I saying the HVAC contractors are doing things perfectly. Most have a long way to go on proper unit sizing (decoupling your profit/pricing from the size of the installed unit is a good start to helping them accept Manual J results), and all the penniless mastic salesmen is a bad thing. Mastic on the plenums and cabinets is prevalent but few contractors are using it on all the connectors. Aluminum foil tape is the popular answer that usually meets the initial duct testing requirements, but will it hold up after multiple years in a scorching Georgia attic? (Regardless, mastic is required – see Section 403.2.4 of Georgia’s Supplements to the IECC)
Tight duct systems are the ultimate goal here, but the hidden lesson in all of this for HVAC contractors is don’t start promising low duct leakage rates to your builders unless you plan on making an additional trip to the jobsite to seal around the boots. For those of you with HVAC contractor friends and acquaintances, remember to show support and remind them, “It’s not your fault.”
To those of you who are putting the ductwork out of the attic and inside the building envelope or using ductless systems, bless you. You obviously get it already.
* Code actually allows three duct leakage testing options: 1) 6% total leakage measured at rough-in with air handler installed. 2) 8% leakage to the outside measured at final. 3) 12% total leakage measured at final.)
Jeffrey Sauls, the owner of D2D Sustainability is a certified HERS rater and Duct and Envelope Tightness (DET) Verifier for the Georgia energy code. His background is engineering, and he has a degree in Industrial Engineering from Georgia Institute of Technology.
Top photo by Ambernectar 13 from flickr.com, used under a Creative Commons license.