In many parts of the country, the smells of fall that fill the air are apples, fallen leaves, and the furnace with its distinct odor of burned dust after being dormant for the summer. Many techs who service gas appliances reminisce about the days of the pilot and belt-drive blower - how wonderful it was to have belts to adjust, pilot orifices to clean, ribbon burners to wash, bearings to oil, and air shutters to adjust to get just the perfect blue cone in the flame with streaks of orange appearing intermittently at the tips.

The Honeywell round T87F was the master control; a 10-loop multiplier wrap and a simple analog Amprobe®, along with a slide of the anticipator, ensured accuracy for a lifetime within ±2° of the set point.

The filter was a simple 16- by 20-inch throwaway; a 16 by 25 would replace 90 percent of the ones you might come across, so you kept a stock of them. The furnace was mechanical, simple, and reliable, requiring just a few adjustments to keep it in peak operating condition.

Then came the 1980s; leg warmers were popular for a reason. Direct-drive blowers, in-shot burners without adjustment, and a hot surface igniter that replaced the pilot were common on furnaces from this era. Heat exchanger designs grew more complicated, making heat exchanger inspection next to impossible.

Later on, the noise of the draft-inducer motor would replace the silent draft hood that had served faithfully for many years. Spill switches were replaced with the mysterious, sometimes infamous pressure switch; oil bearings became sealed; thermostats switched to cycle times rather than anticipation; and the old filter was replaced with a 6-inch pleated accordion type or an electronic air cleaner.

The only thing left to clean was the troublesome flame rod with a new concept called flame rectification. A blinking light in a box replaced the technician without need for adjustment, and the furnace inspection became more of a verification that the box was still in the basement.

While not all of these changes were necessarily bad, many of them were signs that the mechanic was dead and the parts changer was born.


Or so you may have thought! The modern gas furnace requires a more thorough inspection and more careful adjustments than ever.

Low-mass heat exchangers and complicated designs require accurate airflows and gas pressures to ensure their longevity. Safety requires inspection and verification of their safe and reliable operation. Tighter homes make procedures like ventilation air testing and combustion analysis a critical part of all inspection procedures.

Now we need to ask, where do we start? To what standard do we perform the inspection?


A check sheet and some simple understandings will help make your job meaningful again, and provide your customers the protection they are paying for.

An average tune-up on a gas furnace will take 75-90 minutes. Anything less and a technician simply cannot get the required job done.

Keep in mind that with every equipment inspection, there is an implied warranty. It has been upheld in court: Unless the consumer is notified in writing that there is (or may be) a potential problem, the person performing the inspection (you) has determined that the appliance is operating safely and correctly.

Equipment inspections should meet the industry standards as outlined by:

• The National Fuel Gas Code (ANSI Standard Z223.1 and NFPA 54).

• Your state’s building code.

• The Refrigeration Service Engineers Society (Publication 630-92 9/86).

• The Gas Appliance Manufacturers Association.

• The International Fuel Gas Code.

• Many other manufacturers’ equipment installation, operation, and maintenance guides.

When the inspection is performed in its entirety, it will ensure to the greatest extent that the equipment is operating correctly and safely. Doing a proper inspection takes time and practice, but the benefits to your company and your customers will be paid back tenfold in increased comfort, lower utility bills, improved safety, lower callback rates, increased service sales, and higher professionalism for your company.


Lastly, it is not important that a service technician knows everything. What is important, however, is that as a technician you know where to find the information and how to read and interpret an installation or service manual and properly test the appliance and its components to verify safe and proper operation.

Check sheets should always be used as a service tool. They are as valuable for the senior technician as they are for the apprentice. Check sheets keep everyone consistently performing the same inspection techniques and practices.

The checks outlined here are general in nature, but they meet or exceed most appliance manufacturers’ guidelines. While the information is current today, technology and procedures change. If available, use the manufacturer’s recommended service guide along with the information provided here to perform a thorough inspection.

As a technician, you are responsible for keeping up with technology and service and maintenance procedures. If in doubt, always consult the manufacturer.

The information contained here follows the gas heating portion of a check sheet available by request at I would recommend that you make several copies of the check sheet to use on jobs as a reference. A Word file can be requested and customized with your company’s logo or letterhead. A step-by-step guide is also available that details the service procedures at


 Let’s say that it’s 8 a.m., and the Johnson’s have called you out for an inspection. The air is brisk, but Mrs. Johnson will not turn on that furnace until you have inspected it. Mrs. Johnson is a regular service customer and a retired English teacher. Her Gold Furnace Agreement includes her free annual inspection, which she has had for more than 20 years.

When you get there, the furnace is off and the thermostat set to 67°F; the house is 62° except for the kitchen, which is being heated by her stove. A cigarette hangs from her lower lip. You are most likely one of the only visitors she will have in her home. Her Yorkshire terrier, her only companion, jumps up at you for a scratch on the head. Fresh coffee gives the room the smell of the corner café.

Before even entering the house, you started your combustion analyzer. You perform an ambient CO test on every house you enter for everyone’s safety. The combustion analyzer is creeping up … 6, 7, 8 … and you’re not sure if it’s the cigarette, stove, or another appliance elevating the CO readings. With every job, you know you should always check ambient CO levels whether there are smokers or not. If for no other reason, your own safety is important.

The reading stabilizes at 8; you know it’s safe to proceed with testing. With the furnace off, you know it is not the problem, but you will perform a quick check for CO at the stove, and check for proper venting and safe combustion of the hot water tank too. The dryer is electric.

Making sure Mrs. Johnson’s cigarette is the only source of CO is a top priority. While standing near the kitchen, you ask Mrs. Johnson if you can check for CO at the stove; it is running 50 ppm air-free. The stove is well within safe limits, but you remind her it’s safer to start the furnace than to heat the house with the stove. Old habits are hard to break.

Editor’s note: This article is part one in a two-part series. Coming up in part two: Bergmann describes Mrs. Johnson’s furnace inspection in detail. What raised the CO?

Publication date:01/15/2007