Energy Vanguard Blog

Keep Out! - One Place NEVER to Put HVAC System Ducts

Posted by Allison Bailes on Fri, Apr 15, 2011

ducts in vaulted ceiling building envelopeI had lunch yesterday with a friend who's an HVAC designer and HERS rater in North Carolina, and he mentioned the idea of separating HVAC design from HVAC contractors. For that to happen, though, HVAC contractors first have to start doing the design part because most residential HVAC systems are thrown in with little to no actual design work.

Here's an excellent example. See that photo to the left? Do you know what's terribly wrong about installing ducts like that? Let's leave aside the issue of whether flex duct should be used or not. What you see here would be bad even if it were rigid sheet metal ducts.

The insulation should provide the clue you need. Those ducts are going through a vaulted ceiling, and, just as a vaulted ceiling is a terrible place to put recessed can lights, it's also perhaps the worst place you can put a duct for your HVAC system.

Not only does the duct displace insulation, it's also right up against the roof deck. In the summer, that roof deck can get up to 150° F or higher. Inside the duct is air that should be about 55° F. That's a 95° F temperature difference, and all that lies between that hot roof deck and the cool air is, in this case, a little bit of fiberglass insulation with an R-value of 6. Do you think that air's going to come out of the vent at 55° F? In the winter, you've got warm air in the duct next to a cold roof deck, and the temperature differences can be similarly large.

Point for third party HVAC design. Yes, there are a few HVAC contractors out there who do good work, but overall, the HVAC industry needs an overhaul. If you've read my articles and white paper about Version 3 of the ENERGY STAR new homes program, you know that I've talked a lot about how difficult the HVAC part will be. In fact, it may not work without third party HVAC design.


If you're looking for solid HVAC design done by a third party that does it right, you've found it. We do that.

Tags: ENERGY STAR, HVAC, design, building enclosure, heating & cooling distribution