HVAC test and balance

Why TAB agencies rent rather than buy

Most balancing work is done with circuit setters and differential pressure readings. That is fine when the valve is the specified model, installed the right way round, with the right straight run, and the Cv table is correct. When any of that is in doubt, an independent flow measurement settles it, and that need arises on maybe one job in five. Renting for those jobs is cheaper than owning an instrument that sits in a van most of the year.

Working through a building efficiently

• Program the points before you go. Twelve stored configurations means you can set up pipe data for each riser at the desk, then just clamp and read on site.
• Work top down or bottom up, consistently. Randomised order makes it impossible to spot a systematic offset later.
• Photograph every sensor position. When a number gets challenged three months later, a photo of where the transducers sat is the evidence.
• Record signal strength alongside flow. A low-confidence reading that you flag at the time is defensible. The same reading discovered later is not.

Independent verification of circuit setters

The most valuable thing a rental meter does on a TAB job is arbitrate. Clamp on upstream of the balancing valve, in clear straight pipe, and compare to what the valve says it is passing. Disagreement usually points to a valve installed backwards, the wrong Cv table, or a partially blocked strainer immediately upstream.

Where the clamp-on will struggle

Very short pipe runs between fittings, which is common in tight mechanical closets. Ten diameters upstream is a hard requirement, and on a 4 inch line in a closet you may simply not have 40 inches of clear pipe. In that case the reading still repeats, so it is useful for before-and-after comparison, but do not treat the absolute number as certified.