Hi

I’m renovating a 35yr old home which has the water tank exhaust vented through a brick chimney type exhaust stack. I would like to remove the brick stack (which I find is a huge waste of space) and just build a much smaller casing around the vent which I was told is a 4 pipe vent. this will allow me to make my upstairs bathroom bigger by almost 2 ½ ft, & easily opens up my basement more, which in the future could be converted into a suite. It doesn’t look difficult to DIY, take down the brick, then rebuild around the vent. Can these brick stacks be removed? Is there anything that needs to be changed? Can anyone give me advice or redirect to information on what I want to do & if its possible? I posted a picture of the brick stack:

water tank exhaust 2 - View Image - Post Your Image
water tank exhaust - View Image - Post Your Image

Thank you