The Crucial Role of Combustion Analyzers in HVAC Efficiency and Safety

The combustion analyzer is an indispensable tool. It plays a pivotal role in ensuring the longevity of equipment, minimizing callbacks, and safeguarding your liability. Let’s shed light on the importance of this tool and how to use it effectively.

A combustion analyzer is a complex instrument, and understanding its readings is crucial. It's important to familiarize yourself with the specifics of combustible appliances and always consult your manufacturer for details on oil and gas pressures and efficiency readings. It’s also vital that manufacturers’ guidelines should be followed precisely to ensure safety and compliance with warranty terms.

One fundamental principle to remember is that all fuel-consuming appliances require fresh air for complete combustion. The environment housing these appliances must provide sufficient combustion air.

In the realm of modern gas burners, the primary air is controlled by the burner itself, while the secondary air ensures complete combustion. As a technician, your adjustments are limited to gas pressure and combustion air which can be adjusted on some gas burners as well as oil burners.

When using a combustion analyzer, you'll measure oxygen (O2), carbon dioxide (CO2), and efficiency. It's important to monitor carbon monoxide (CO) levels closely, given its potential danger.

It's essential to remember that the efficiency of a furnace is determined by its design. When using a combustion analyzer, you're assessing the efficiency of the burn, not adjusting your AFUE ((Annual Fuel Utilization Efficiency). AFUE is a measure of how efficiently a furnace converts fuel to energy over the course of a heating season.?

To ensure accurate readings, it's crucial to use a high-quality meter equipped with a built-in NOx filter.

Excess air, the calculated air that passed through the combustion process, is necessary to ensure complete combustion. Draft, the measured pressure difference between atmospheric pressure and flue pressure, comes in four types: natural, induced, power, and balanced.

When testing a Atmospheric draft furnace’s, the test should be taken under the bonnet at each heat exchanger section, as testing in the flue can lead to inaccurate results due to air dilution. For an 80 percent furnace with B vent, both inner and outer pipes should be sealed. The flue pipe should be sealed with a testing cap or brass plug and high-temperature RTV caulk that doesn't harden, while the outer pipe can be sealed with foil tape.

Testing 90 percent furnaces involves drilling a hole in the PVC flue and using a brass threaded male plug with non-hardening high temp RTV. While this is a common practice, technicians should be aware of local regulations and manufacturer guidelines regarding modifications to venting systems. It's important to note that metal tape is not an acceptable way to cover the test hole on a 90% furnace

In conclusion, combustion analysis is a must for HVAC professionals. It offers more accuracy than older methods, and without it, you're essentially guessing. After calculating proper nozzle sizes, orifice sizes, oil and gas pressures, and inputs, an analyzer should be used. Remember, we can't make an appliance more efficient than its design. We need to match fuel input consumption per OEM specs and set proper fan speeds so our temp rise falls within the furnace temp rise range.

This article is adapted from the CE HVAC Tech Tips podcast hosted by CE Customer Assurance Managers. Available on Apple Podcasts and Spotify.

Jack Cauffman and Brooks Whitson

Note: All the information shared in this article is intended for licensed HVAC professionals. Only trained and qualified personnel should design, install, repair, and service HVAC systems and equipment. All national standards and safety codes must be followed when designing, installing, repairing, and servicing HVAC systems and equipment. The Contractor is responsible for meeting local codes, standards, and ordinances.