On 10/31/2016 9:36 AM, trader_4 wrote:
On Sunday, October 30, 2016 at 12:06:45 PM UTC-4, Ed Pawlowski
wrote:

That vent may be very important. It may be the source of air for
combustion.

If it's a gas WH in a closet, it could be critical. If it's in a
wide open basement, then it's not.

My last house (built in 59) had the gas water heater and gas furnace
inside the same closet located inside the house. The vent was a grill in
the closet door. Lived there 30 years and never once flooded the house.
Came close one time though. Happened to hear a hissing noise and saw a
tiny leak spurting out. The water hadn't left the closet yet so I was
very lucky.

BTW that model furnace had two doors, top-burner-vented and
bottom-fan-sealed. No interlock. People would sometimes leave off the
bottom door after cleaning/repairing the fan. The fan would then suck in
the gasses from the burner compartment above and spread them
throughout the house. That furnace was used in thousands of houses in
the area and caused many medical problems over the years.