My Undersized Ducted Mini-Split Heat Pump
Last year my wife and I bought a 1961 ranch-style house, and I've been having a lot of fun fixing it up. I wrote about the problem with the spray foam in the attic not covering the top plates and…
duct design
17 Steps to Better Duct Systems
If a 12 step program is good for helping people deal with addictive behaviors, then a 17 step program ought to be better, right? Or maybe it's just a random number that fits the number of tips that popped into…
Busting a Myth About Low-Static Ducted Mini-Splits
I like mini-split heat pumps, especially of the ducted variety. And because I don't like to pay for a lot of excess power, I prefer to use ducted mini-splits with smaller blower motors operating at a low total external static…
The Third Worst Place to Put a Duct
Ah, so many choices. If you want to design and install a duct system to create problems, the possibilities are endless. I've certainly written about a lot of them (as well as how to do it properly). Today, though, let's…
Is Low Velocity Bad for Air Flow in Ducts?
It's obvious that moving air too quickly through ducts can be a problem. Faster air means more turbulence, more resistance, and more noise. But I run into people who think that low velocity also can be a problem in ducts. …
The Unintended Consequences of High-MERV Filters
What is a hair's breadth? A strand of the finest human hair is about 20 micrometers (also called microns) in diameter. Take a piece and slice it in half. Then take one of those halves and slice it in half…
What Happens to Air Flow in Ducts When Size Changes?
As we continue our study of indoor air quality and filtration, we now come back to duct design. Today's lesson is on an interesting bit of physics that applies to anything that flows. It could be heat or particles or…
Friction Rate Is the Wrong Name
Last year I wrote some articles on duct design and one of the topics I covered was this thing called friction rate. At the end of that article, I discussed "How to think about friction rate." It confuses a lot…