#friction rate

Tech Tips:

A few weeks ago, I was hired to consult on a multi-family new construction project. The building was already framed, and the ducts were roughed in. The owner of the building was concerned with the quality of the ductwork. He noticed that the HVAC company was not following the mechanical engineer's plans. This was my […]

Manual D Speedsheet Walkthrough

Bryan recently released a podcast on rules of thumb and how they can really get us in a pickle with sizing ductwork. With that in mind, I thought this might be a good time to do a walkthrough of Manual D from start to finish on a project I just finished up. My good friend […]

The Friction Rate Chart (and What it Means)

A lot of proper duct design comes down to an understanding of available static pressure and friction rate. We've covered this topic several times on this site and the podcast, but I wanted to focus on this ACCA chart specifically (shown above). If you want a deep dive, I highly recommend listening to my podcast […]

How to Determine the Friction Rate for Residential Duct Design

This article is written by one of the smartest guys I know online, Neil Comparetto. Thanks, Neil! Recently, I posted a question in the HVAC School Group on Facebook that went like this: “When designing a residential duct system, what friction rate do you use?” As of writing this, only one answer was correct according […]

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In this short episode, Bryan talks about the situations when permits are not needed to install HVAC/R (or HVAC/R-related) components.

A few codes are universal in residential HVAC, including the International Residential Code (IRC) and the International Mechanical Code (IMC). The local municipality, also known as the authority having jurisdiction (AHJ), chooses which codes to adopt.

You do not need a permit to install plug-in, cord-connected appliances. However, you need UL-listed plugs. You can also replace plugs without needing a permit, but the ratings need to be correct. Anything less than 25v that doesn’t put out more than 50 watts of energy also doesn’t require a permit. Thermostats and many IAQ accessories, including UV lights, fall into this category.

Portable heating and ventilation appliances, including space heaters and portable cooling units or dehumidifiers, also don’t require permits. Evaporative or “swamp” coolers also don’t need a permit for installation. Self-contained units with 10 pounds or less of refrigerant and are actuated by motors with