For people working in the building performance, weatherization or HVAC industries, we recommend you carry and use a combustion analyzer, personal CO monitor, draft gauge, and a smoke pencil. These products help to insure your client's safety, your safety and to determine the safe operation of combustion appliances. While you may not be qualified to correct the combustion problems you may find or create, you must, at minimum, know if the problems exist. If you are not qualified, licensed or trained to make repairs to a heating system, please consult a qualified and trained HVAC contractor, preferably one who has been formally trained in with dealing with issues of Carbon Monoxide (CO) and combustion testing.
When it comes to combustion analysis, we wrote the manual. No kidding, we really did! Down load it here for free. TruTech Tools Combustion Guide