Everyone has now figured out what happens when you tightly seal up a room with a combustion appliance in it: Tightening a home’s envelope may reduce the air supply needed for combustion, and when there’s not enough combustion air, equipment could have combustion ventilation problems. Thus, the people who sealed up homes (often referred to as the weatherization industry) needed a way to determine if sealing a home up would undermine the safe operation of combustion equipment. To meet this safety need, they embraced combustion appliance zone (CAZ) depressurization testing.
The basis for the CAZ test, as we now know it, was two documents: ASTM International Standard Guide for Assessing Depressurization-Induced Backdrafting and Spillage from Vented Combustion Appliances — designated as E1998-02 — that has been reapproved numerous times. Additionally, a Canadian depressurization test standard, CAN/CGSB-51.71, was recalled and is no longer in use.
Like many tests done in the field, the results of a CAZ test are only good for the conditions in place on the day and time it was performed. Kind of like judging the whole year’s weather around conditions you saw from the porch at sunset on Oct. 3. Thus, for CAZ testing, the result is: It is safe today, hopefully, which means it will be safe later today and for ever more.
Fortunately, if the combustion system is operating unsafely all of the time, or at the time of testing, the combustion equipment will fail the CAZ test. When one of the three main combustion problem indicators are found — backdraft, combustion spillage, or flame rollout — weatherization specialists have generally called in HVAC experts to resolve the issue. In many instances, there may be a point score provided. The tests commonly used do not report failures at equivalent levels of depressurization. However, a failure is a failure, and the underlying cause needs to be fixed.
After any failed CAZ test, all HVAC-related equipment evaluations and the related combustion analysis testing should be completed by a professionally licensed HVAC contractor who employs qualified technicians with the appropriate certifications and training. Hence, the CAZ razzmatazz, since the original conditions for the test can rarely be duplicated and may not be the same when an HVAC technician gets there. Further, HVAC technicians should be told how the failure was determined and what the operating conditions were (outside temperature, wind direction and speed, what combustion equipment was operating, etc.).
When called to a CAZ test that has failed, the HVAC expert may need to become a home-performance expert to diagnose the real problem. For example, a failed CAZ test indicates there is a problem, not where the problem is or what is causing it. Often, the potential performance problem can be with the venting, in the appliance, or it can be related to the way appliances were installed and/or the operating conditions. Once identified, the cause of a CAZ test failure may be a combination of unrelated factors. Thus, the furnace is often operating properly. If the HVAC technician does a combustion analysis and simply reports the furnace is OK and leaves, the homeowner still has a problem. Why miss the opportunity to investigate and find a cause and a solution for the customer?
For example, one set of new homes was failing the CAZ tests, and, worse yet, homeowners were suffering from carbon monoxide poisoning. You should be able to guess who got the blame and the first callback. The homes had condensing furnaces with their own combustion air and exhaust venting, so they were not the problem. Unfortunately, when it comes to CO, HVAC contractors are often considered guilty until proven innocent. In the case of these new homes, the hot water heaters, gas dryers, and gas ovens did not have any combustion air provided when they were installed. Thus, the solution was to design a venting system that could provide more combustion air when the other appliances were in use (or open the windows when they were in use). By identifying the problem and developing a solution, the HVAC contractor avoided the danger of letting the judicial system try to figure out who was at fault. Additionally, their relationship with the homeowners was repaired and strengthened.
For detailed information on CAZ testing, ACCA members can download the “Understanding CAZ Depressurization Testing” technical bulletin. The CAZ testing information is also included as part of ACCA’s Qtech basic home-performance training course, which is available online.
Publication date: 3/7/2016
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