I sealed up the windows and the attic ductwork last week only to end up with a major air leak into the attic someplace.

It's so bad that I had to disconnect and tape open the drier vent in order to get the furnace exhaust to go up the chimney and not into the house. I have a fuel oil furnace with a (gun style) blower.

I have asked around town for smoke pencils and nobody has a clue what I am talking about. I have blower fans that I can use to pressurize the house for the test.

Questions.
1. Is there a way to make a "Slow match" or smoke pencil?

2. If not, is there someplace I can order one online?

3. Since I no longer have a gas hot water heater, Can I block off that leaky flap thing on the chimney?

PS: I'm in northern MN and it's expected to get down to -20f outside tonight.