Working high steel was a bit nerve-wracking. Walking on two-inch wide bar joists while maintaining your balance was not for the faint of heart. Scanning the help-wanted section of our local paper, I spied an opening for a plumber with six years of experience — experience I did not have. In the early 1970s, landing a job in the mechanical trades was not easy, as all employers wanted only those who had prior experience. The job market back then was tight. I called the owner who outright rejected me. Undaunted, I called him daily until he finally relented and granted me an interview. Walking through his shop building, he peppered me with questions: Know what this is? What’s this used for? Where does this get installed? I admitted I had no clue instead of lying, which must have impressed him because I got the job!

My first day at work was a total surprise. I anticipated there would be additional workers but it turned out I was his lone employee. I waited outside his office thinking we would be off to some mechanical adventure as he imparted some mechanical wisdom for me to absorb. Instead, he handed me a worksheet for a no-heat call and the keys to the truck! Upon arrival at the customer's home, she showed me to the mechanical room and, thankfully, left me alone with their Burnham (now US Boiler) category-one chimney-vented gas-fired boiler. Yikes!

I at least knew enough to remove the front cover and read the “How to light the pilot instructions.” I followed them to the letter, including the several-minute wait between attempts. But, after holding the pilot button down for one full minute, the pilot would immediately go out when I let up on the button. My boss arrived and asked me if I had figured out the problem and I told him what I had tried. He pointed and said “Do you see the skinny copper thing the pilot flame hits?” Yes. “That’s called a thermocouple. There’s some on the truck. You’ll find them. Go ahead and fix the boiler.” He left and I did repair the boiler. That’s how I got my start in the trades, and my boss seldom helped me with the service calls.

I moved on after only three months to work at F. W. Behler, where I served as an apprentice under highly experienced journeymen. After almost four years at Behler, I moved on to work for another mechanical contractor who also threw me into the deep end of the pool to either sink or swim! “Here’s a no-heat call for an oil-fired boiler.” But I’ve never worked on oil burners! “Neither have we. You’ll learn.” Same drill for well-water pumps and water treatment systems!

In the early 1970s, most fossil fuel boilers, furnaces and water heaters were Category-one appliances. I don’t recall exactly when I became aware of categories for fossil fuel appliances, but have no doubt, it was early on during a seminar or class. Category one appliances are gravity-vented using galvanized metal pipe and fittings that are not airtight. Room air will be drawn in through gaps even when the appliance burner is operating, unless, of course, the mechanical space is under negative air pressure! Whole house fans can cause back drafting, drawing the byproducts of combustion into the home or business and I have personally witnessed this happen on multiple occasions.

Cat-1 appliances operate at or below 83% efficiency producing minimal flue gas condensation except on the initial cold-start where some condensation will occur as hot flue gasses come in contact with the room-temperature metal flue piping. That initial flue gas condensation is quickly dried out by the hot flue gasses warming the metal flue piping and the same issues will be happening in the masonry chimney, providing it is also sized properly.

Cat-II appliances operate above 83% efficiency, produce acidic flue gas condensation, and also rely on gravity to vent combustion byproducts. The NFGC (National Fuel Gas Code) defers required venting materials for Cat-II, III, and IV to whatever the manufacturers’ instructions dictate. The IMC (International Mechanical Code does recognize single-wall galvanized metal can still be utilized for Cat-1 appliances, but under limited circumstances, which they cover extensively in Chapter 5: Chimneys and Vents.

On more than one occasion, local inspectors thought our combustion venting would need to be altered before it would pass inspection. It pays to read and follow the manufacturer’s printed instructions and each time this happened, we would help them understand our installation complied with the instructions.

Cat-III and IV appliances are both positive-pressure exhaust systems. Cat-III appliances operate at or below 83% efficiency while Cat-IV operates above 83% efficiency and produce copious amounts of sustained flue gas condensation that needs to be treated before being discharged into the DWV (drainage, waste, and vent) system. For natural gas-modulating condensing appliances, it’s not unusual for 1 gallon of acidic condensate to be produced for every 100,000 Btu of gas burned. If the home has a low-temperature radiant heating system, there will likely be in excess of 1,000 gallons of acidic condensate with a pH of 3 to 5, which will eat through cast iron drainage piping, leaving a ribbon of missing pipe along the bottom.

Don’t be surprised if the local inspector doesn’t understand Cat-IV combustion venting. On more than one occasion, local inspectors thought our combustion venting would need to be altered before it would pass inspection. It pays to read and follow the manufacturer’s printed instructions and each time this happened, we would help them understand our installation complied with the instructions. The codes also defer to the manufacturers’ instructions as prevailing over what’s in the code book passages. Ignore, or worse yet don’t bother opening, reading, and understanding what the manufacturers dictate, at your and your customers’ peril. If the installation and operating instructions call for you to use a combustion analyzer to properly set up combustion, then do that. Provide a copy of the combustion analysis for your permanent records, a copy to keep with the I&O manual, and one for your customer, too. If an issue arises at a later date, that combustion analysis may well be your get-out-of-jail-free card!

Appliances and mechanical devices were so much easier to work on back in the early 1970s and if you were mechanically inclined, you could most likely work your way through troubleshooting and repairing all manner of products. Imagine hiring some wet-behind-the-ear kid today and sending them out for a no-heat call on a modcon boiler or mini split inverter heat pump. Or a clogged sewer: “Here kid, take this sewer machine and go clear the sewer line blockage. Don’t worry, you’ll figure it out.”