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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Many technicians who work on fuel-fired equipment will admit they’ve singed their eyebrows when watching a burner light. It’s a rite of passage among most seasoned technicians. What if there was a safer way to check ignition instead of sticking your face in front of a burner? Fortunately, there is, and it involves using a …
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Chances are high that you’ve encountered disastrous equipment replacement jobs you’d love to forget. Whether it’s the customer who now has high humidity issues, or the system that can’t maintain temperature anymore — we’ve all experienced them. Indeed, in many of these occurrences, attention to detail and avoiding bad industry habits helps prevent the occasional …
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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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Zero Draft and the CO Conundrum

Many technicians get distressed when they measure draft pressure in the flue and discover the reading is zero. Let’s look at three common reasons for zero draft pressure in a flue. We’ll also determine what defect you’re dealing with. Reason #1: Zero Draft from Building Depressurization Building depressurization is probably the most common reason for …
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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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