The combustion safety testing part of Chapter 8 of the RESNET standard is being revised and we are wrestling with all the issues raised in your blog post “Questioning Worst-Case Depressurization Testing”.  I have sent a link to this blog to the RESNET performance testing subcommittee so that they can see all the good stuff you folks are discussing (I am the chair of the subcommittee).


Issues with Worst Case Combustion Testing

The literature review one of the key results of the LBL summary, titled: Assessment of Literature Related to Combustion Appliance Venting Systems, was that the worst case depressurization test isn’t a very robust test.  By that I mean that this test often produced false negatives and false positives and was sensitive to weather.

The Problems

Too many false negatives and false positives means that you are doing a test that is not helpful.  You are missing out in identifying homes with problems and wasting effort remediating homes that are actually okay.  Also, the test can be sensitive to weather, such that you get different answers depending on when you test and you can’t confirm test results on another day, or with another technician, even if all the interior doors are in the same positions during both tests.
With multiple appliances and CAZs (combustion appliance zones) the worst case depressurization testing becomes very time consuming and confusing, because you have to capture all possible combinations of doors open/closed, burners firing/not firing, fans   operating/not operating, etc.

A Possible Fix

So what to do?  I think that checking the venting to make sure it meets code/NFPA requirements and installing good CO alarms are simple and straightforward ideas.  Beyond that, rather than measuring pressures maybe we should check for draft/spillage  under “normal” conditions (CAZ door closed, all other doors open, no local exhaust/dryers or other combustion appliances (including furnace/A/C blowers) operating) and then test again at “worst case” where we turn everything on.  The whole rigmarole with which doors to open is a time consuming and non-repeatable part of the worst case combustion safety test – so how about we just leave the CAZ door closed and open all other doors.  That is simple to learn and do and is repeatable.  It isn’t perfect, but I think you would be able to find most malfunctioning appliances.  What do you think of this approach?