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

Step 2:

Location is everything, you want easy access. Drill hole, clean sharp edges, remove any metal shavings.

Step 3:

Line the edge of the hole with duct tape.

Step 4:

Tear off a 3" length of duct tape and fold over about 1/2", inflate a balloon inside the duct, twist the open end a few times and secure twisted end with tape. When the exhaust is in operation cover the hole with tape. I've been doing this for about a year now and can reuse a balloon 4 or 5 times before replacing it.