Static Pressure and Manometer Basics

In this class, Bryan gives the Kalos techs a refresher and goes over the basics of static pressure. He also differentiates between utility manometers and precision manometers, covering their appropriate uses.

Utility manometers are your typical standard service manometers; they are designed to measure pressure in inches of water column ("WC, "H2O, or inWC). Inches of water column are smaller units of measure than PSI, and they're ideal for static pressure and gas pressure. Some utility manometers have one port, and others are dual-port manometers. Single-port manometers require you to zero them with the hoses on before taking the measurement. (Accurate zeroing is very important, especially as pressure continuously changes with the weather.) Dual-port manometers are often used for measuring a pressure differential, and zeroing is typically less critical because there is already another baseline for comparing the pressure.

There is no such thing as "zero pressure." The closest we can get to "zero" pressure is 14.7 PSI, atmospheric pressure, so zeroing out single-port manometers is critical.

Precision manometers use Pascals instead of "WC, which is a much smaller scale. We use precision manometers to measure duct leakage or envelope leakage (such as through a blower door test). We can also use the tiny Pascal scale to measure pressure imbalances between rooms and mitigate pressurization/depressurization problems.

Static pressure probes look an awful lot like pitot tubes, which have tubes within tubes. A pitot tube takes a measurement that's a combination of static pressure and directional force. Pitot tubes then subtract the static pressure to yield only the velocity pressure; these tools require precision manometers to do their jobs properly. Pitot tube usage is more common on the building science side of the industry than HVAC service.

Static pressure probes each have a closed end at the tip and some side ports, and they only measure static pressure. The probes face the opposite direction of the airflow and measure the force exerted in all directions (against the walls of the duct). Static pressure can be either positive or negative in reference to the atmosphere, and we typically measure it by putting one tube in the return before the blower and the other above the blower in the supply plenum in a fan coil or handler on a heat pump or straight-cool A/C (or below the coil on a gas furnace). In gas furnaces, the coil provides a pressure drop and is separate from the actual unit.

The rated static pressure can be found on the data tag; a static pressure that differs from the rating will affect the system's performance (though there is typically an operating envelope). If the static pressure is higher than the test static on the data plate, a variable-speed blower will have to ramp up to maintain the airflow, increasing operating costs and the amp draw while negatively impacting the motor's longevity. Filter changes can cause the static pressure to change over time. You can also measure pressure drops over the filter and evaporator coil to isolate problems with filters or coils.

Static pressure is NOT airflow; it's a pressure measurement, but it can be an indicator of airflow. Before we can measure the static pressure accurately, we need to make sure the system is producing the proper airflow (high-stage, no dehumidification mode). Although checking static pressure isn't something we need to do on EVERY call, it's worth checking when there are airflow complaints. Total external static pressure, supply, and return static are all worth checking to see if there are restrictions across filters or coils or other possible airflow problems.

Filters can cause many problems, and static pressure readings can help you pick up restrictions caused by filters. Larger filters (4") with greater surface areas tend to create far less of a pressure drop and last longer than shallower filters (1"), which can clog and restrict airflow quickly.

[HVACUncensored]

This is an awesome Video Bryan. Very informative. I’m gonna pass this along to our techs. One the best detailed videos I’ve seen to properly explain Static Pressure. Hope all is well buddy.

[shannonhill]

Damnit man I live in Florida and want to come work for you guys at Kalos so bad. Tired of begging for training, classes, and certifications as if they just have handfuls of employees trying to actually better themselves around here or something.

You’re a wizard, man. Please don’t stop. We out here learning thanks to you and Craig.

[pelmqku]

I am Korean. I always think your lectures are the best.

[francismarotta]

I wish manufacturers would put in test locations for manometers

[marshallnmoonshine]

Great video. I do HVAC at a hospital and we do a LOT of air balance and static pressures. We always take a static pressure differential across final filters on the maintenances. Recently I took a bunch of Pitot readings to evaluate plugged chillwater coils to see if they need replacement.
It was definitely a learning curve.

[skylerlewis]

Love your videos man! I’ve been doing residential HVAC in Utah for 8 years. We’re 4, 500 feet above sea level here. Almost every system I test has high static pressure. It’s almost standard that we are adding 300 to 500cfm of return duct work on every install that we do. Also having issues with pressure switches not staying closed even though the inducer is pulling 30% over the water column rating of the switch. Keep up the awesome work, I’ve learned a ton from your videos and I appreciate the content 🤘🏼

[gowkarranpooran]

Hi Bryan, These videos are awesome. IT brought me back on track and I have to give you the Cedit, for guys in the field who cannot afford hvac school this is such a blessing. Your teaching really took me to a high level with great HVAC etiquette. Honest and perfect diagnostics no guess work hence time saving and quick solutions. I thank you very much and may God bless you and keep you and yours for being so selfless. Gowkarran from Toronto Canada

[rvamom]

My 6 year old has been making us binge watch your channel lately 😅 he loves it!

[nelsonv]

Another great video Bryan, you explain static pressure very clear. Thanks

[robertwasswa]

I can not stop to appreciate what I learn here and apply to Temporary HVACR as a gas/oil Tech in Canada. Thanks a lot again, am asking that you guys come over North for a HVACR symposium. We would like to hear and get this information. Truly helpful and problem solving information. Thanks again.

[MAXPILOTO]

Thanks Brian for an awesome video, I learn every day .

[michaelmaclachlan]

Great tip for using masking tape to seal filters that don't quite fit.

I also like to use silicone and/or foil tape in cases where the filter box is not properly sealed with the rest of the duct work.

[I_name_All_my_guns]

Watched twice. Learned something each time. Saved to watch again and again and again

[jorgeaguila]

Outstanding as always, Thanks for sharing!

[jamesmooney]

Enjoyed vid. After watching, clear as mud. I'll watch a few more times.... Thanks for posting this info.

[tymitunie]

I love this guy.. don't listen to him because he is right and every word he says is true. but my company is based on correcting mistakes related to " your field duct workers" attempt to save on material and installing undersized ducts and I will never install 1" filter rack if you pay me!.. media filters!.. I listened to every word of his lesson and I wanted to applaud that we are lucky that there are still people who understand and know what they teach.. this was great to listen to.. stay true my friend!

You my friend have 👍🏻👍🏻👍🏻 and a sub.

[justwork_hvac]

Thank for the great video. Very informative

[coldfingersub]

Excellent lead into using DEEP PLEATS HIGH MERV efficient filters on Correct size. Of course measuring pressure drop or following the chart printed on the side of the filter and always recommend upsizing.

[jasonjohnsonHVAC]

Another tip to add to your discussion....if you use the different airflow ramping profiles on a variable speed for the humid ramping profile, where the blower will ramp up to 50% for 30 seconds then 70-75% of full speed for 7-7.5 minutes, then it finally hits 100% full speed. Wait till you get to full speed....or change the profile to a non humid profile, where it'll ramp to 50% for 30 seconds and go to full remember to put dip switches back to what its supposed to be for the location you are at.

[lynncomstock]

Charging any AC or HP system correctly ASSUMES correct rated airflow which is usually 400 cfm per ton. This is a big point that should be emphasized.