Poor mans blast gate for laser exhaust or dust collector

I live in Alaska, when it gets cold it really gets cold, and stays that way for 7 months.To keep the cold air out of my workshop I needed to insulate the ducting and add a blast gate. Insulating was easy but I didn't want to hack up the ducting to install the gate.soooo. 

Step 1:

What you'll need:
portable drill
1.5" hole saw
duct tape ( the first time I've used it for it's intended purpose)
round balloons