The previous poor duct examples of the last couple of days are unfortunately not as isolated as we would like. And that’s what we often see duct leakage rates of 30% or higher–that 30% of the air that you’ve paid to heat or cool making it’s way outside. Not very energy-efficient even is you have a 95 AFUE furnace or an 18 SEER AC. You can good ductwork, sized properly, with smooth transitions, well sealed, and especially if outside your home’s envelope, properly insulated.
Dave Stecher and Duncan Prahl of IBACOS–a company that does research into how buildings work and helps builders and contractors do a better job doing the right thing–forwarded these doozies. I won’t show you the whole house’s ducts, just a representative example:
Here’s a planned floor joist, hopefully (ah, hope spring eternal with shoddy building practices) directing air to a register. Using joist and stud bays as duct work isn’t a good idea to begin with, even if done “well”. These cavities are difficult to seal making leakage a problem. And they’re not conducive to good air flow. But picture this sheet metal filling the space (before it was peeled back), and you’ll get the picture of what it looks like.
Now, even when using sheet metal to block air flow, we find leaks at the wood intersections. How well do you think sweaters and t-shirts work? That’s what was stuffed on the back side!
Yes, a sweater and a t-shirt. Not your standard building materials. But I guess they were handy and installation probably only took a few seconds. At the right are the articles of clothing. I’m wondering if someone has a photo of a leg from a pair of blue jeans used as a duct run. I’ve also got some old shoes and a bike helmet–any ideas how I can make them part of my HVAC system?
The fixed transition here gives you a better idea what the transition should look like. The duct, transition, and boot are all directly connected and sealed. We typically use mastic to seal, but the foil tape here looks like it is the proper type of duct tape (not the cloth stuff).
You can take the lowest bid or you can insist that the job gets done right. The two often don’t happen together. And if the job isn’t done right, you’ll usually pay more in the long run pumping your conditioned air outside. Which approach do you prefer?