How to determine if the chimney draft is correct

Two months later I finally found the right search string to get an better answer than 'light a stick on fire'.

Whenever preforming a test for safety, you always want to choose a worst case senator.

According to this page, worst case chimney draft conditions happen when the house is fully sealed and all exhausting appliances are activated. Thus one needs to:

• Shut all windows and doors
• Turn on all bathroom and kitchen exhaust fans
• Turn run all appliances that exhaust such as dryers and central vaccumes

The source fails to mention whether or not to fire up other flue based heating sources. However my intuition tells me that heating devices that don't share the same flue as the test should be fired up, but ones that are common to the device being tested should be left off because the added heat might add to the updraft)

Similarly, the source fails to mention what the temperature differential should be between the inside of the house and the outside should be as there will clearly be more of an updraft when the air inside the home is warm, and the outside is very cold. For a furnace / heating stove, this likely won't matter as you'll always be operating under ideal conditions. However with a water heater, you may run into the case where you have a high outside temperature, AC chilled ducting, and short heater run times such that the flu never gets hot enough to create an updraft. This would be your worst case, attempts to run your test when conditions most closely mirror this situation would be preferred, but may make less of a difference than the other items listed above.

According to the reference, once you've sealed your house and started up all venting appliances, your can simply tur on the appliance you want to check for several minutes then cup your hands around the fume hood without touching it and feel the air draft. However, the manuals for professional draft testing equipment say that their tests should be preformed within the first 60 seconds after igniting your appliance. Thus it seems the best next step would be to:

• Light a long match stick or dense cardboard strip (like a pizza box) and then blow it out so it smolders and smokes
• Turn on your appliance and place your smoke stick near the vent hood.
• If the smoke goes up the hood, your vent passes
• If the smoke appears to be being blown into the house, the you have a down draft, and should repair it (especially if the down draft persists after your device has been on for several minutes).