Virtual Combustion Testing

February 25, 2013
March/April 2013
A version of this article appears in the March/April 2013 issue of Home Energy Magazine.
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As any BPI Building Analyst will tell you, it’s hard to become adept at combustion testing. It takes lots of practice, in real houses, with real mechanical equipment. No amount of classroom training is a good substitute. Unfortunately, many training programs don’t provide much hands-on time.

Steve Mann
is a HERS rater, LEED AP+ Homes, Certified Energy Analyst, serial remodeler, and longtime software engineer. (April Wise Photos)

When I got certified, we spent several days in a classroom and one day on-site at a test house with about eight other students, and then we took the written exam. It was up to each individual student to schedule and take the field exam. We had to buy or borrow equipment, and practice on our own house and the houses of any friends who were gullible enough to let us mess with their furnace, water heater, and oven. Then we had to track down a proctor and a test house, and take the field exam. It was nerve-racking, and success rates were not that high.

More recently, there are job-oriented training programs that put you in the field for several weeks before you take your exam, which is an ideal situation. However, there are still training programs that throw you out there like mine did. The question is, how can you get lots of practice if you’re not enrolled in an intensive training program that provides hands-on practice?

Figure 1. During testing, the screen always shows the Toolbox on the left and appliance icons on the bottom.

Figure 2. A typical CAZ (Combustion Appliance Zone) will include an open vented furnace and water heater.

Figure 3. You can zoom in on combustion appliances, like the water heater, to turn them on and off.

Figure 4. The combustion analyzer has working buttons that let you change its settings.

Figure 5. The detailed User Feedback report lists every item you should have tested and how you did on that item.


One possible solution is simulation. Although there are limited scientific studies done on this topic, it has been shown that simulation-based training, when added to classroom training, improves student outcomes significantly. There are other benefits as well. Students can practice at their own pace and on their own schedule. It’s less expensive to deploy, and—particularly important for combustion training—simulation poses no physical risk. Perhaps best of all, you can record details about a student’s performance and use those details to enhance the student’s learning and track his or her progress.

Simulation-based training has been used for years in the aviation, medical, and military fields, among others. It is most appropriate when the content is

  • cognitive, requiring reasoning and perception;
  • procedural, involving finite, identifiable processes; and
  • variable, with changing event details.

Combustion testing, and more generally building science, have these three attributes.

A few years ago, InterplayEnergy of Del Mar, California, realized that the cost of developing training simulations had dropped to the point where they could be cost-effectively used for trade training. Simulation training no longer required the big budgets available to military or aviation institutions. Using CEO Doug Donovan’s background as a HERS rater and BPI Training Developer, he and his team developed InterCAZ, a web-based simulation for teaching BPI combustion-testing skills.

Shall We Play a Game?

InterCAZ lets the user navigate through a three-story house containing combustion appliances and related equipment, and simulate combustion testing of those appliances. There’s typically a natural-draft water heater and a furnace located in one or more of the rooms. There’s a laundry room with a gas-fired dryer, a kitchen with an oven and cooktop, a fireplace, and several ventilation fans.

To successfully complete a simulation, you have to enter the house; find the appliances; set up worst-case depressurization; and test spillage, draft, and CO. If any appliance fails under worst case, you retest under natural conditions, per BPI’s protocols. In addition, you have to sniff all the natural-gas lines, take an ambient CO reading, and take oven and cooktop CO readings. You record all results, identify failures, and make recommendations according to BPI action levels. All your work is scored against a “perfect” scenario. You can view or print out a detailed analysis of your performance to pinpoint your weaknesses.

The real benefit of InterCAZ is its variability. You can run the simulation as many times as you like. Each time, the combustion appliances and their locations change. The building pressures change, forcing you to work through a full worst-case depressurization analysis. The appliance performance characteristics also change. One time, the water heater and furnace may draft perfectly; another time they may fail miserably. There are more than 30 variables that change from run to run.

InterCAZ lets the user navigate through a three-story house containing combustion appliances and related equipment, and simulate combustion testing of those appliances.

Using InterCAZ

When you first start up InterCAZ, you are located outside the house. The left-hand side of the screen contains icons for items you need to complete your simulation—a Toolbox, a Clipboard for recording your test results, a Help screen, and buttons for quickly moving from one floor to another. The Toolbox, shown in Figure 1, includes a personal CO monitor, combustion analyzer, gas sniffer, safety goggles, manometer, smoke stick, and thermometer.

Along the bottom of the screen are icons for all the combustion-related equipment in the house. When you turn on an item, such as the furnace, the Furnace icon lights up. By scanning the icon list, you can quickly and easily determine the state of all the equipment in the house. Both the list of tools and the equipment list are visible at all times while you are running the simulation.

You navigate through the house using the Arrow keys on your keyboard to simulate walking. This can be very awkward at first, but after running three or four simulations, you get the hang of it. You can also jump between floors by clicking on the Floor icons on the Tool palette. Once in the house, you click on doors to open and close them, click on ventilation fans to turn them on, and click on combustion equipment for a close-up view. Figure 2 shows a water heater and furnace in the basement. Figure 3 shows a close-up of the thermostat of the water heater, which you use to turn it on and off.

To complete a simulation, you walk through the house, turn things on and off as necessary, and test the combustion equipment using your tools. Figure 4 shows the combustion analyzer being used to measure the water heater flue gases. (Note: You can tell that the water heater is turned on—its icon is highlighted in yellow.) The combustion analyzer actually has buttons on it that you can use to take flue gas or ambient CO readings.

As you do your testing, you record your results on the Clipboard. You also make recommendations based on your findings. When you’re finished, you click on End Sim and Submit Answers in the lower right-hand corner of the screen. You are then given an opportunity to view your results in a detailed User Feedback Report (a sample is shown in Figure 5). The report lists all the items you should have tested for the simulation, the results you should have gotten, and whether or not you got the correct answers. This very detailed report is an excellent tool for gauging just how well you understand the BPI protocols.

The Bottom Line

InterCAZ has a Training mode, which walks you through two specific scenarios. You can also run an unlimited number of simulations at Beginner, Intermediate, and Advanced levels. This web-based product is an innovative tool for teaching BPI combustion protocols. It can help build the confidence of someone with limited field training. It’s also a good tool for someone preparing for the field exam or for brushing up the skills of someone with extensive experience.

Having said that, InterCAZ does have limitations. For instance, it doesn’t really simulate the act of going into a new house every time. The floor plans are all the same, the location of the ventilation fans is always the same, there’s always a fireplace and a gas oven in the same place in the kitchen. The only things that move are the combustion appliances. You always use the blower door at 300 CFM50 to simulate fireplace draft. Gas sniffing is always the same, and cooktop CO readings are always 2 ppm, at least in my tests. The laundry room window is always open when you first enter the house. This predictability can make you lazy after a few simulations.

Furthermore, InterCAZ doesn’t test all the possible types of equipment or configurations you might encounter. There are no closed-combustion appliances, for instance. There is only one water heater and one furnace. They are either in the same or in separate CAZ, with individual or combined flues. At most, you’ll have two CAZ. These combinations cover many of the most common situations, but the real world isn’t always so simple.

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Get more information about InterCAZ.

Despite these limitations and other minor complaints, InterCAZ is a useful tool for helping someone learn BPI combustion testing. It’s not a substitute for real field training, but it is a valuable companion. As a bonus, you can get BPI continuing-education units for using it and getting a score of 85% or higher on one simulation at all three experience levels. Retail prices range from $85 per week to $249 per year.

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