Arkansas HVACR NewsMagazine May 2024

HVACR NewsMagazine May 2024

Tech News

Adequate Air at a Glance and Why Modulating Dampers in Any System is a Poor Choice.

Converting tonnage air flow requirements from inches to poster board size is game changer. The practice makes recognizing the need for an upgrade much easier for the salesman, technician, and homeowner. For basic size requirements, we take the CFM necessary and divide by two. For a one and a half ton (nominal) system we need 300 square inches of return at a minimum. This relates to a 16x20 poster board. The equivalent is seldom found in typical construction. We see these size grills where equipment in the 1.5 to 3 ton systems are installed. And things go down from here. A three ton (nominal) system will require a 20x30 poster board for comparison. We see 30x20 returns grilles employed widely on 5 ton systems. Finally, the largest poster board regularly sold, is a 24x36 board. This size poster board identifies five tons (nominal) of air and is still just under one square foot too small . Your customer will grasp this comparison easily. When the customer doubts your numbers and asks why the first company didn’t get it right, you can justify you position since evaporator coils have become increasingly dense with fins per inch count on the rise. Today’s air handlers and furnaces handle air much more efficiently than did older equipment. Most homes have the equivalent of the 18”x24” no matter the equipment size.

We have discussed insuring adequate system air many times here. Everyone thinks of formulas, static pressure measurement, or other criteria to chase down elusive air requirements. Along those same discussions, we have concluded a filter in the bottom of any furnace or air handler is a thing of the past. We should never use the factory default for filtering to assure proper air flow. Filters are now known as an insurance policy for system performance and evaporator replacement. Without efficient filtration, the entire mechanical system is at risk. I will state flatly that only one cursory measurement is actually required upon a repair or sales call. If everyone gets used to understanding the option, you will only pull out a measuring tape after the sale is made and you will become keenly aware of restricted shortages with only a glance. You can always true up your estimate or repair cost after the sale. Since over 80% of homes are short on return or as identified in heating dominate climates, cold air return, we should become familiar with what adequate air intake looks like from a physical dimension rather than numbers on a page. A square inch description never conveys an accurate picture of area.