Be careful who you recommend. Most plumbers don't have a clue about this stuff. You want someone knowledgeable in venting, pressure diagnostics and equipped. That means a combustion analyzer, draft gauge, and micromanometer for starters.

Too much to speculate on. Need to consider the installation itself, the Combustion Appliance Zone (CAZ), the interaction of the house with the appliance, geographic siting and weather to name a few. While you may suspect leaky return ducts or a clothes dryer causing depressurization of the CAZ, only testing will confirm it.

Be careful with the term "backdrafting"-that is a diagnosis. Have you witnessed this phenomenon? Was it sustained for more than 45 seconds? How did you confirm the backdraft?

While such markings are clues to a problem, they are not a diagnosis unto themselves. Instead of recommending a particular trade, just state the capabilities you feel he needs such as I mentioned above. If a plumber comes in, checks the draft with a mirror or blows out a match, then later it does backdraft and causes an injury, you may be party to a "negligent referral".

FYI, look to Dale Feb's FIRE Service in a few months for a certification program for such training.

HTH,
Bob

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