Air filters create resistance to airflow that can reduce a fan’s ability to move air by up to 50%. You can evaluate the filter’s impact on airflow by measuring the pressure drop over it. It takes less than a minute to do. It is often the diagnostic test that identifies the problem in nearly one …
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Measure TESP in HVAC Two-Piece Air Handlers

What makes modular or two-piece different from their single-piece cousins when it comes to measuring total external static pressure (TESP)? In this article we’ll examine the differences and discuss how to measure TESP correctly. “As-Shipped” The “As-Shipped” idea is helpful when measuring the TESP of two-piece air handlers. So, what do you find when you …
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Testing HVAC Static Pressure

I hear a lot of reasons for taking static pressure measurements on every service call. One of the most common is that it takes too long — there isn’t enough time on a call to do it. Let’s face it, technicians have a lot of responsibilities and measuring static pressure adds to them. What if …
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Challenge is measuring static pressure on a variable speed fan

Measuring static pressure on air handling equipment that has variable-speed fans can be a challenge to both new and experienced technicians. By addressing a few details, your readings will be consistent when you encounter this blower type. Let’s look at three tips you can use the next time you measure static pressure on a variable-speed …
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HVAC Air Filter Media

If you’ve been in the HVAC industry for any length of time, you’re familiar with complaints involving dust and dirty equipment. As a result, most technicians target the air filter first when they receive such calls. As you investigate these problems, keep in mind how the following ways reduce filtration effectiveness so you can more …
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Stacked pebbles represent stability in HVAC systems

When testing and diagnosing the operation and performance of an HVAC system, the timing and measurement are critical. Ideally, the system should be calling for full heating or cooling, and fan speed so it can reach a stable operating condition. Let’s take a closer look at what constitutes stable operating conditions so your test data …
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CO - What Do You Know?

Many HVAC professionals assume the leading cause of carbon monoxide (CO) poisoning is a cracked heat exchanger. This assumption leads to inaccurate test methods that pass on from technician to technician. They try to assure customer safety, but unknowingly rely on misinformation. No one wins in this scenario — both the contractor and customer have …
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Avoid sharp turns

Flex ducts could be in imminent danger. A few months ago, I wrote about a recent proposal to severely limit the use of flexible (flex) ducts. Due to poor installation methods, the International Association of Plumbing and Mechanical Officials (IAPMO) is proposing to limit use of flexible duct to only five feet in length. How …
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HVAC Airflow and leaf blowing -- the common denominator

Let’s talk airflow. We live back in the woods on a half-acre with fifteen 100-foot tall oak trees. For years I’ve imagined sharing leaf blowing airflow lessons with my fellow airheads. Let’s take a look at the mad airflow skills you can master while blowing leaves. Fascinating Statistics “If you don’t measure, you’re just guessing.” …
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Flex duct cost savings

Flex duct versus metallic duct: for decades many considered duct material the key to how well an HVAC system delivers airflow to the conditioned space. You should start paying closer attention to this discussion. Events unfolding over the next few months could ultimately determine how much flexible duct you will be allowed to use when …
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