Gas water heater venting connected with a box

[wstowell (William Stowell)]

Two gas water heaters have connected vent pipes. The one vent runs through this box (without a bottom) and then over to the second water heater vent and then on into the chimney. Never saw this setup before. Is it legit?

[lkage (Larry Kage, CMI)]

@wstowell

Two gas water heaters have connected vent pipes. The one vent runs through this box (without a bottom) and then over to the second water heater vent and then on into the chimney. Never saw this setup before. Is it legit ?

Utilizing an atmospheric draft hood is fine if the water heater is designed for it.
You’ll need to look up the make and model installation instructions online to know for sure.

But, to me, it does look like they removed the draft hood because of height and fabricated an atmospheric draft hood to slap on there. But the vent pipe is still too high.

At any rate the exhaust cannot run downhill like it does at my arrow.

This diagram will help understand a way to do it more safely.

[jvillegas2 (Jose Villegas)]

Should be slopped upward a 1/4" per foot to prevent downflow. This can prevent the gases from leaving the house properly and cause a backdraft. just taking a stab at it. Study study study.