“I don’t even own a combustion analyzer,” said every hydronic hack ever. I’m baffled that, in 2025, I still hear this phrase a few times a year from “heating professionals. Look, I’m not perfect. My technicians aren’t perfect. Learning is a never-ending process. Not owning and knowing how to use a combustion analyzer, however, screams apathy and laziness. Sure, cast-iron and steel boilers are less prone to the pitfalls of imperfect combustion, but there’s absolutely no excuse for someone who services or installs condensing appliances to avoid the use of an analyzer.

It’s almost as if customers could use one simple phrase to filter contractors before hiring: “Please show me your combustion analyzer.”

It’s not optional

An analyzer allows me to leave a jobsite knowing — without a doubt — that I’ve done everything in my power to ensure that my customer has received the highest efficiency, greatest service life and complete safety after I’ve installed a boiler. There are serious service benefits, too. 

If you know what you’re looking for, signs of boiler trouble are easy to spot: soot buildup, nuisance lockouts, strange odors and customer complaints about uneven heat or high fuel bills. However, without an analyzer, those symptoms are treated with guesswork and part-swapping instead of data-driven diagnosis. Skipping combustion analysis is a fast track to callbacks, wasted fuel and broken trust.

Maybe I was a little harsh at the beginning of this column. If you’re a young helper and heating pro reading this column, it’s possible nobody has ever taken the time to fill you in on combustion analyzers. If so, read on. 

Combustion analysis is the process of measuring and interpreting the gases produced by fuel-burning equipment — such as boilers, furnaces and water heaters — to ensure safe and efficient operation. Technicians use an electronic combustion analyzer to measure oxygen, carbon monoxide, carbon dioxide, flue temperature, draft pressure and efficiency. 

When this information is correctly applied, heating technicians can dial in air/fuel ratios and detect potentially dangerous or inefficient conditions.

Think of it like ordering a full blood panel from your doctor. The patient might be symptomatic, but without the blood test, the doctor is only guessing at how best to treat the ailment. Same goes for a technician working on a boiler.

The dangers of skipping combustion analysis

One of the biggest risks in skipping combustion analysis is missing unsafe levels of CO, which is odorless, colorless and lethal. An appliance may be firing, the flame may “look fine” and yet CO levels could be creeping into the living space due to incomplete combustion, poor draft, partially obstructed intake or a cracked heat exchanger.

In any of these scenarios, the appliance might still run, but incomplete combustion could drive CO levels dangerously high. Relying on a visual inspection or just checking the temperature rise doesn’t cut it. Combustion analyzers provide hard numbers that help you spot CO anomalies before they become emergencies.

Improving your customer’s ROI

Energy savings and comfort drive word-of-mouth marketing. Failing to fine-tune combustion hurts your customer and your company.

Even if a boiler system appears to be operating as intended, it could be wasting fuel. Whether it’s over-firing, under-firing or running too cool and condensing when it shouldn’t be, inefficiencies cost homeowners money. That reflects poorly on you.

A properly tuned system (which is only possible with the use of an analyzer) burns with the correct fuel-to-air ratio, transfers the maximum amount of thermal energy from the heat exchanger to the system fluid, and produces low CO with stable flame characteristics. 

Neglecting combustion analysis means fuel efficiency can fall year after year, costing your customers money and leading them to call someone else when their bills get too high.

Optimizing service life

The only thing worse than high fuel bills is the need to replace the boiler before the customer was expecting to, especially if you installed the unit.

Improper combustion doesn’t just waste fuel; it damages equipment. 

Excess air can cause flame impingement or flame lift; this stresses heat exchangers. Over-firing leads to overheating and metal fatigue. Acidic condensate from improperly tuned conventional boilers can corrode heat exchangers. Short-cycling is hard on all components.

Skipping combustion analysis often shortens system lifespan. There’s no better way to lose a customer. 

Icing on the cake

When you perform a combustion analysis, you’re not just adjusting screws. You’re proving your professionalism. Pulling out a combustion analyzer shows that you hold yourself to a higher standard. It tells the homeowner you care about their safety, comfort and energy bills.

Leave behind a copy of the printout or report or, at the very least, tape it to the boiler cabinet. Explain what the numbers mean. That kind of transparency and education builds trust and generates referrals.

There’s one more benefit that people don’t often like to talk about. When you — as a licensed professional — walk off a jobsite, you were the last professional to touch that system. Should a catastrophic event occur, your use of an analyzer allows you to pull up a time-stamped record of the boiler’s status upon your list visit.

God forbid you ever be taken to court for an issue with a system you installed or serviced, but if that happens, you will have proof that you left the appliance in peak condition, operating in accordance with manufacturer specifications. This is a cheap insurance policy.

Analyzer tips and tricks

• An analyzer is useless if it’s not calibrated. Check it annually or as recommended by the manufacturer.

• Use flue connections that feature test ports. If it’s an existing unit without a test port in the flange, drill a hole and seal it afterwards. Be certain no material gets into the heat exchanger while drilling the hole. 

• Run the appliance for a few minutes to allow the burner to stabilize before testing.

• Compare the readings you gather to the appliance manufacturer’s specs; these can be found in the manual or on the rating plate.

• Take before-and-after readings to document improvement; keep that info in a file for the customer.

• Print and save the report. I like to hand one to the customer, tape one to the boiler and keep one for my records.

In our business, trust and results go hand in hand. Combustion analysis isn’t an optional step. It’s a core part of safe, professional service. Skipping it isn’t a victimless crime. It hurts the system, it hurts your customer and it hurts your reputation. If you’re not analyzing your systems already, it’s time to step up your game.