Last week, we briefly looked at the spec sheet of a gauge manifold. All things considered, it was quite short; we only had to worry about the refrigerant types, pressure ranges, and hose diameters. However, manometers’ spec sheets are quite a bit longer than gauge manifolds’ because they have resolution and accuracy specs, among other things like battery life and pressure ranges.

Manometers also have some application-specific considerations; just as CO2 refrigeration techs need gauge sets that can measure the immense pressures of transcritical CO2, home performance techs need manometers that can capture tiny pressure measurements. While most technicians will do just fine with an everyday manometer for measuring static and gas pressure, technicians on the building performance side will need a manometer in a completely different league.

Basic Manometer Usage

We use manometers for a few different reasons: measuring static pressure, measuring gas pressure, and sometimes even quantifying pressure differences between zones. We can comfortably use the inches of water column (inH2O, inWC, “w.c., etc.) scale for things like measuring static and gas pressure. However, that scale is far too large for measuring pressure differences between rooms or between the building envelope and outdoors; we’ll need Pascals (Pa) for that.

It’s also worth mentioning that some manometers, like the digital Fieldpiece SDMN6, are dual-port manometers that can help you interpret differential measurements. While these are helpful for things like determining static pressure drop over components, you must ensure that they read independently of each other if you’re taking gas pressure measurements or measuring static pressure at a single point.

Most of the manometers we use nowadays are either digital or probes. Analog manometers still exist; you may have heard of the Dwyer Magnehelic before. These measure differential pressure, and there’s no reason to have a separate Magnehelic if you already have a solid digital manometer or probe set. 

Manometers vs. Precision Manometers 

Let’s look at the Fieldpiece JL3KM2 probes (top) and the TEC DG-8 digital manometer (bottom): 

The specs aren’t presented the exact same way, but we need to note the accuracy and range of each tool, which are provided in both cases. The range of the JL3KM2 is 0–60”wc, and the DG-8’s is -10–10”wc. That tells us that the JL3KM2 is capable of dealing with larger pressures but not the negative pressures we’d encounter in the building science part of the trade. Meanwhile, the DG-8 can measure as low as -10”wc (almost -2500 Pa). Both tools are manometers, but they have vastly different applications and potential uses.

Additionally, while the JL3KM2 can measure pressure on the Pascal scale, it has an accuracy tolerance of 5 Pa up to 498 Pa, meaning that your reading could be up to 5 Pa off from the exact pressure. The accuracy tolerance is even larger once you exceed readings of 498—1.5%. However, the DG-8’s accuracy tolerance in the Pa scale is 0.9%. When reading pressure differentials between zones, low numbers like 3 Pa are common, and the 0.9% accuracy tolerance means that the reading only has the potential to be off by 0.027 Pa when properly calibrated; that's even smaller than the tool’s resolution (0.1 Pa). The DG-8 is much more accurate with those finer pressures and is the clear choice for zonal pressure diagnostics or testing for MAD-AIR.

Does that mean the DG-8 is better for everyone? No, it doesn’t. The DG-8 checks off all the boxes for a precision manometer you’d use with a blower door or for zonal pressure diagnostics. However, the JLKM2 is very accurate for the job it’s been designed to do, which is to measure static and gas pressure. The DG-8 is also more than triple the price of the JLKM2; since both of them have negligible accuracy tolerances in the inches of water column scale, it makes more sense to go with the JLKM2 for everyday field use. 

I said it last time, and I’ll say it again: it’s all about application. Can this tool do the work you need it to do (measure within the range of values you’ll see) exceptionally well (with a respectable accuracy tolerance)? If the answer is yes, then you don't need much more than that; the rest will come down to price, durability, and even personal preference.