For disclosure: One of our divisions designs

where to start? (For disclosure: One of our divisions designs, sells and installs fully Customized AHU (Air Handling Units), so I’ve got over a decade of engineering, sales and hands-on experience all mixed together Strength: Typically, double skin, a.k.a. double wall, AHU construction is stronger. It will flex less. As the AHU operates across varying conditions (CFM, pressures, temperatures, humidity) the skin will flex, expanding and contracting. It is not only possible to measure this, but measuring the flex (known as deflection testing) is highly recommended. A good rule of thumb is: ‘the less flexing you have, the higher the unit’s quality’. Of course there are exceptions to this, but having seen every brand under the sun, and having walked inside every major AHU brand (yes, I’m talking 50,000 CFM+ units that are as big as a mobile home and bigger), unit deflection is a very good indicator of overall build quality. Without going into the engineering aspects of material strength, moments, etc., double wall/double skin construction is almost always going to be stronger. However, the thickness of the double skin is not always indicative of how strong a unit is. I can point you to some non-engineering resources that can illustrate this for you. For example, an article on our website: Healthcare HVAC and AHU Replacement goes over some basics of why, for many applications, a double wall AHU is best. We also did a pretty cool time-lapse video that has made the rounds in the commercial HVAC industry, including leading engineers, the biggest healthcare groups in the U.S., pharmaceuticals (yes, the big ones), and tech-manufacturing: MonMan Air Handler Replacement Video I put this video here because it literally shows you how a true custom, double-wall air handling unit is built from scratch. (It’s time lapse and moves quickly, so it’s easy to miss the details; I’d recommend changing the YouTube playback settings to half speed or even 0.25x speed for certain parts.) Many specifications default to a standard wall thickness of something like 4″ thick, or even 6″ thick. The usual reasoning behind this is that the thicker the unit is, the more insulated it is. I feel that is largely a fallacy. Most of the AHUs we install for our high tech and healthcare customers are 2″-3″ thick (the thickness of the walls.) It is simple to meet most R-value insulation requirements with polyisocyanurate foam filling the entire cavity between inner and outer skins. If you want a 6″ thick unit, you’re just being excessive, wasting space and money. A single wall unit (like a residential or light commercial AHU) will almost always be single wall. You’ll have a cheap, galvanized sheet metal box that flexes, bends, rusts and breaks. And on the inside, you’ll often see some cheap fiberglass insulation. I have a huge problem with single wall units with fiberglass insulation. The fiberglass can get wet. It can breed mold. (We did an extensive microbiological study in a hospital - one of the largest hospitals in the U.S. when you count number of patient beds - and single-wall air handlers were a big culprit: The Top 5 Weird Bacteria Hiding Inside Your Hospital.) And the little things, like rodents, that can easily get into a single wallAHU, and start nesting in the insulation, that few people think about unless they are an HVAC technician and have to work on the AHU. Yes, I’ve seen mice, rats and squirrels living, reproducing, and all their other bodily functions, right inside an air handling unit, in the middle of a hospital mechanical room that serves patient areas