Can three water heates use one vent pipe to the exterior?
Common venting is fine if sized appropriately.
Looks good on the picture to me not counting the missing cover (shield) on the far left one at bottom.
Where are you located Mr. Sedillo? If you’re in CA, I see another issue.
That is a commercial washer and dryer, so the application of appropriate air make up is needed.
That looks like it would fail a gas test and should have a much bigger common vent for 3 water heaters, according to where I am anyways.
Good catch ( That is a commercial washer and dryer )
I do hope they have a good air make up and have Heater exhaust checked as is it big enough ?
Based on the California code,my two cents would be ( including some of the above observations):
Good make-up air for the whole compartment would be required.
Its doubtful that the two FVIR w/h’s are getting enough air.
Condensation signs on the left hand wall indicate excessive air moisture.
Plus the commercial laundry apps.
Full bore isolators are req’d on each w/h c/w supply.
Accessible gas isolators are req’d for each appliance.
The 30" x 30" workspace before the w/h rule - req’d for maintenance or w/h replacement.
Outer door missing from the burner cover.
I would briefly check behind the gas dryer and at its external vent hood for any signs (fluff) that all is not well.
Carefully examine the developed length, the stack, and the terminal of the common vent - & check if the FAU vent ties in down the line?
Are CO & heat/smoke alarms present?
The lower seismic straps are too high.
No bonding present - if code req’d.
From what i can make out, the common vent is adequately sized but only eyeballs on site could determine this.
I’m a new guest to nachi.
How does one contact the moderators?
This interesting OP seems to me to be in the wrong forum - perhaps, the Plumbing Forum would be a best location?