I'm in the same situation, though my basement is as leaky as a sieve, and I haven't anything about it to keep air going to the boiler.
So, I can see a few possibilities:
- Make a vent in the wall. This will pretty much undo all of your sealing efforts.
- Deliver outside air through a PVC pipe to the burner, as you proposed. You still have a hole-in-the-wall situation, but at least the burner is sucking in colder air. This is usually good, but in this case it may turn out that your boiler is tuned to intake air @ room (basement) temperature. When the burner is off thn you are still getting a rush of cold air.
- PVC pipe with some kind of damper, which allows fresh air in only when the burner is fired up. This would be ideal, but the valve actuator would have to be failsafe. Or maybe not - if the valve doesn't open, then a CO sensor should let you know.
- Upgrade to a boiler with a closed combustion chamber. These are more efficient (90-95%, 107% for condensing models), but are very expensive.