Side by side water heater and furnace venting

Tried searching for a list of acceptable venting methods and couldnt find one. I know the smaller btuh appliance cannot be below the larger but what are the rules on side by side for 2 gas fed appliances (water heater and furnace) into a shared chimney? Thanks for any help with this

The larger appliance should come in behind the smaller. Side by side is amateur installation and may result in poor and or improper draft for the smaller appliance. Also, the connections should be secured with sheet metal screws, not tape.

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Thanks simon yea they duct tape is another issue I’m writing up.

Looks like the tape is holding a misfit connection also.
The small btu vent should be up higher.