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Five Combustion Test Instruments Every Heating & Air Conditioning Technician Should Own

Oct. 31, 2023
If you haven’t verified combustion safety, now is a great time to begin. Let’s look at five essential combustion test instruments you need to start.

Many HVAC technicians may find themselves ill-equipped to perform their jobs this fall heating season. They won’t have the test instruments, skills, or time to test and diagnose fuel-fired equipment. As a result, they could end up guessing if the equipment is safe. If a combustion problem exists, they will never know. This lack of knowledge leaves the technician, their company, and customers open to potential risks.

Good test instruments are a necessary part of any technician’s daily work. They are not an option. The right gear makes your work easier while helping you to measure invisible HVAC system traits that could reveal harmful conditions. Carbon monoxide (CO) is one of those hidden properties and a critical part of combustion safety.

If you haven’t verified combustion safety, now is a great time to begin. Let’s look at five essential combustion test instruments you need to start.

Personal Low-Level CO Monitor 

A personal low-level CO monitor is the first test instrument you need. Before you test any equipment, use this device to measure ambient CO levels in any space you enter. Rule number one is to make sure the air you breathe is safe. 

Good test instruments are a necessary part of any technician’s daily work. They are not an option. 

An excellent personal CO monitor should have a digital readout and audible alarm at a minimum of 15 ppm (parts per million). I currently carry a Sensorcon Inspector - Industrial Pro. In the past, I have also used models from Testo, UEI, CO Experts, and an NSI 3000. Regardless of the model you choose, keep it with you and be sure it’s turned on. This single device could keep you from walking into a dangerous environment.

As you measure, it’s essential to keep any readings in context. Personal CO monitor readings  tell you if CO is in the ambient air but won’t identify the source. You’ll need other test instruments that measure flue gas to track down the source. Be aware that there are times when you’ll
find no measurable CO in the ambient air, but equipment CO problems still exist.

Combustion Analyzer 

A combustion analyzer is the second test instrument you need to test and diagnose combustion problems. This instrument’s primary purpose is to measure flue gas. For diagnostics, an analyzer should measure at a minimum:

  • Carbon monoxide (CO) – 0 to 2000 ppm+
  • Oxygen (O2) – 20.9 to 0.1%
  • Flue temperature – up to 999°

The analyzer must also continuously measure, so an internal pump is critical. External aspirator bulbs in the probe assembly that require constant squeezing won’t cut it for proper equipment testing.

 Also, if the analyzer doesn’t have a magnetic case, make an extra investment. Not only does it protect your analyzer, but it also provides a way to mount it to equipment. This feature makes the display easier to see when testing.

I’ve been impressed with the Sauermann line of combustion analyzers. They recognized what technicians need in a quality analyzer and built their instruments around those concepts. An important feature they have is the ability to read remotely with a smartphone or tablet. In addition, you can screenshot those readings and upload them to the customer’s file history. 

Regardless of the combustion analyzer brand you choose, keep it calibrated according to manufacturer specifications. Keep your investment running in tip-top shape.Draft Gauge

A draft gauge is the third test instrument you need to test and diagnose combustion problems. We measure draft in inches of water column (in. w.c.), which should always read a negative pressure. At the minimum, look for a draft gauge that measures up to one-tenth of an inch of pressure (.10-in w.c.). Pay special attention to the -.01-in. w.c. to -.02-in. w.c. range on the display. That is the design draft pressure for various natural draft and fan-assisted equipment. 

The Dwyer 460 draft gauge is inexpensive for most draft pressure measurement applications. Unfortunately, according to their website, Dwyer has discontinued production. I mention it here because you can still find them online, and they work so well. I’m hopeful Dwyer sees this and reconsiders their decision.

Many combustion analyzers also have a draft pressure measurement built into the probe assembly. This function works well for 80% fan-assisted equipment. However, if you test atmospheric equipment with a drafthood or barometric damper, you need a draft probe accessory placed in the right location to measure correctly. 

The draft gauge determines if adequate combustion air is available for the equipment and that no building pressure changes interfere with equipment operation. Contrary to popular belief, draft cannot verify proper equipment venting. Yes, you read that right.

Combustible Gas Leak Detector

Another important part of combustion safety is ensuring no combustible gas leaks. Depending on who you ask, testing methods range from bubble solution to a Zippo lighter (please don’t use the lighter method). A combustible gas leak detector should be a priority to safely and quickly discover gas leaks. 

Contrary to popular belief, draft cannot verify proper equipment venting. Yes, you read that right.

With any test instrument, you get what you pay for. Purchase a quality detector with sensitivity adjustments and both audible and visual alert indicators. An adjustable probe to access tough locations is another important feature. Read the instruction manual and know how to use the detector before searching for gas leaks. I’ve had great luck out of the Bacharach Leakator 10. It’s a reliable combustible gas leak detector that meets all the criteria above. For years, it has been my go-to instrument for gas leak testing. 

You might think, “I don’t need no stinking leak detector! I only use bubbles!” No worries. You still need to use bubble solution, just less of it. The bubbles serve as visual verification of a gas leak. When choosing a bubble solution, look for one that clings to the pipe and doesn’t run off immediately once you apply it to the line or fittings. 

Before you test, if you smell a strong gas odor, it’s best to contact the gas company immediately. Don’t take any unnecessary risks. When in doubt, play it safe. 

Digital Manometer [MW3] [DR4] 

Low fan airflow is a leading cause of cracked heat exchangers and primary limit cycling. This issue influences combustion safety. To diagnose this problem, you’ll need a manometer to measure equipment static pressure. Excessive total external static pressure (TESP) often contributes to low airflow, leading to heat exchanger failure and limit switch trips.

Digital manometers are versatile and can test pressure switches, inducer motors, and gas pressure. Fieldpiece makes great manometers that will fit the needs of many service technicians for basic testing. I like the JL3KM2 manometer kit. It’s versatile, and they fit easily in a meter bag. However, if you’re looking for higher precision, a micromanometer might be the instrument you need. The DG-8 from TEC (The Energy Conservatory) is my high-precision manometer choice. The team at TEC designed this device with the HVAC industry in mind. 

Besides a manometer, you will need the following accessories: 

  • Pressure tubing (neoprene or silicone works great)
  • A static pressure tip
  • A step bit or 3/8-in. bullet-tip drill bit with a sheath
  • 3/8-in. test port plugs
  • An assortment of tee, barbed, and gas valve fittings
  • A dedicated carrying case or bag.

Most residential blowers operate at a maximum rated TESP of .50-in. w.c. If you measure TESP and it exceeds the equipment’s maximum rated TESP, investigate a potential airflow problem. 

An Investment in Safety

You may have noticed that I didn’t mention a lot of test instrument options in this list. I wanted to cover the top five that many technicians don’t currently own when they come to an NCI Combustion Performance and Carbon Monoxide Safety class. The other test instruments you already own also play a role in assuring proper equipment operation. 

Investing in the five test instruments I discussed increases your diagnostic abilities and gathers much more troubleshooting information. Once you have the right test instruments, learn how to use them to serve your customers well. When used correctly, these instruments will quickly pay for themselves.

David Richardson serves the HVAC industry as Vice President of Training for the National Comfort Institute, Inc. (NCI). NCI specializes in training focusing on improving, measuring, and verifying HVAC and Building Performance. 

If you’re an HVAC contractor or technician interested in learning about how to test and diagnose combustion safety issues, contact David at NCI’s website,, is full of free information to help you improve your professionalism and strengthen your company.

 Editor's note: David Richardson's product selections are based on his preferences, and are not to be viewed as endorsements by Contracting Business.