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    In Praise of the Mighty Magnehelic

    Aug. 1, 2011
    Airflow diagnostics are good for your customers and your company, and you already have one of the most powerful tools in the business in your truck.

    Service technicians face an interesting dilemma. The tools we use in our customers' homes help us solve problems in a reactive manner, after a problem or damage has occurred. It seems that we don't find many occasions to use our tools proactively. We use tools when we've been called because a motor has failed or an ignition module is suspect.

    Wouldn't it be cool if we had a way to use our tools to find rather than fix problems? What if we used tools that created work almost every time we used them?

    I’m going to let you in on a secret. You probably have a really cool tool in your truck right now that will create income on a majority of your service and tune-up calls with just a little bit of extra effort: a good old Magnehelic™ gauge.

    We all know that service agreements are a valuable component of HVAC service companies. They help us address one of the industry's longest-running and most vexing problems: feasting in the summer and winter, and starving in the spring and fall. Service agreements help, but they don't seal the deal. When used during a tune-up or service call, airflow diagnostic tools such as Magnehelic gauges and electronic pressure meters can truly help create additional income on a majority of calls, and smooth out our companies' cash flow.

    The National Comfort Institute has measured the performance of thousands of duct systems across the country, and found that the average HVAC system in the U.S. delivers just 57% of its rated capacity. The large majorities of those under-performing systems have undersized ductwork, plugged coils, and dirty blower motors.

    I'll stick my neck on the chopping block and say that if you're like most HVAC companies, you've been looking past undersized returns, restrictive air filter arrangements, and plugged coils during your tune-ups. Not knowing what you've missed, you're even giving the tuned-up system your very own personal stamp of approval. It's time for that to change.

    If you already own a Magnehelic gauge, chances are that you picked one up for a specific purpose years ago; probably because someone told you to measure pressure in water column inches at one time or another. If you don't own one, you can pick one up for less than last month's cable bill.

    If you don't know how to use one, it's simple:

    The Magnehelic is attached to a static pressure tip with a rubber hose. The pressure travels through the tip and the hose, then moves the needle on the gauge. To use a Magnehelic gauge, you'll need to drill 3/8-in test holes into duct and equipment at the right locations.

    To measure total external static pressure in a system with a furnace and a cooling coil, drill a test hole into the blower compartment in the front of the equipment. (Inspect for circuit boards first.) Insert the probe and take and record the return (suction) pressure reading. Then drill a test hole into the side of the furnace, about 1½-in. from the edge. Insert the probe and take and record the supply (discharge) pressure reading.

    Add the two readings together to find total external static pressure. Compare the measured pressure to the maximum total external static pressure listed on the equipment nameplate.

    If the measured pressure is lower than the rated pressure, congratulations. If the fan speed is set correctly, the odds are that system airflow is acceptable. If measured pressure is higher than the rated pressure, the system is like most in the U.S., and airflow is far below what's required.

    The good news is nearly every static pressure problem is fixable, so you've just found a new way to serve your customer. And that's only one way to use a Magnehelic gauge to find and fix airflow problems in an HVAC system.

    Using an airflow diagnostic device such as a Magnehelic gauge goes beyond just the technical use of the instrument. You can also use it to educate (and impress) your customers. You might be surprised to learn that many customers love tools just as much as we do. They especially like tools that look technical, but that they can understand.

    Imagine the following conversation:

    Technician Bryan: "This instrument is called a Magnehelic gauge. We use it to measure your HVAC system's pressure. It's like when a doctor takes your blood pressure. If the pressure is higher than that stated by the manufacturer on the unit nameplate, then it’s likely your ductwork is too small."

    Customer: "What happens if the duct is too small?"

    Technician Bryan: "If the duct is too small, the system can't produce the required airflow. Since airflow is the life-blood of the system, we know we need to improve the duct system. Undersized ductwork really kills energy efficiency."

    Customer: "Why, because it can't breathe?

    Technician Bryan: "Exactly, just like a person’s blood can't flow when his or her veins or arteries are clogged."

    Customer: "Wow, that's a cool tool."

    And guess what: impressed customers will tell their family and friends.

    Customer: "I had my furnace serviced today and they used a really cool meter to figure out that I have undersized ductwork. They're going to fix the problem, which will make my system more efficient, my home more comfortable, and save me money, too."

    Friend: "Wow, I wonder why I've never seen my guy do that?"

    It's incredible to think that somewhere over the last 75 years we lost the value in such a simple pressure measurement. I wonder if it's because Magnehelic gauges aren't made of anodized aluminum with billeted parts? What would happen if we painted our Magnehelic gauges bold yellow? Would we use them more? Maybe we would; in fact, digital manometers work the same way as Magnehelic gauges, but have big digital displays that convey strength and authority. We can't help but feel that as the meter speaks, we must listen.

    So, do a favor for yourself, your company, and your customers: Dust off that old Magnehelic gauge and start thinking about how to put it to work. You'll find work where there seemed to be none before, your customer is going to be more comfortable and save energy, and you'll feel really good about your chosen profession. Few things are better in a person's career than living and breathing the role of a true professional.

    By the way, if you already use a Magnehelic gauge as part of your regular tune-up routine, then kudos to you. You're one of the elite who has discovered the proactive power of airflow diagnostics.

    Bryan Lee is an HVAC contractor in Fresno, CA, and a trainer with NationalComfortInstitute.com. He can be reached at 559/227-9569 ext. 101, or by e-mail at [email protected]. Rob Falke from the National Comfort Institute (www.nationalcomfortinstitute.com) contributed to this story. For a free static pressure test procedure, visit www.contractingbusiness.com/staticpressuretest.