High-Velocity HVAC Systems – GreenBuildingAdvisor – GWC Mag

Member SNMC is thinking about installing a high-velocity HVAC system for his new home in Climate Zone 7A. A high-velocity system uses an air-handler that distributes air at a higher pressure through smaller diameter ducting, increasing the rate of airflow and, theoretically, its efficiency. (For more on velocity and airflow rates, see The Best Velocity for Moving Air Through Ducts.) The smaller ductwork is also supposed to be easier to install in tight spaces. His builder’s HVAC vendor recommended the system; the vendor told SNMC that high-velocity systems have been used in residential builds.

SNMC goes on to say that a heat pump will be the primary HVAC driver. He also plans to install a hydronic system in the finished basement with a TV/rec room and spare bedroom, which he hopes can provide auxiliary heat to the upstairs space. (He admits that hydronic systems are expensive, but thinks the comfort is worth the cost.)

So, is a high-velocity HVAC system a good plan? This is the topic for today’s Spotlight.

Do drawbacks outweigh benefits?  

Both Patrick Osullivan and Peter Engle testify to high-velocity systems’ ability to cool things down in the summer, and Engle says they are very good at dehumidification. Osullivan had a Unico high-velocity system in his home and says another benefit is that the smaller ductwork can be placed where larger ducts can’t fit.

Generally, though, the members posting in this thread don’t show a lot of love for high-velocity systems.

On the subject of size, members DCcontrarian and Akos add some insight. DCcontrarian writes that “high-velocity systems are rare in new construction, and … they’re usually used in retrofits, where they can be used in places where there’s no room for ductwork.” Akos points out that while the systems’ branch lines…