By following the NFPA 54 guide lines or the AGA or GAMA
Depends on what type of vent system water heater has.
a direct vent water heater is more fuel efficient (cost's less to operate). aside from that there isn't much difference, aside from not needing a double wall flue through the roof on a standard gas water heater.
yes there are direct vent gas water heater available Absolutely NOT
B-vent pipe.
yes it can
Yes, you can
When you cannot use B vent to find a way to vent the HWT through to the roof!
No it can not.="h2headingh2"style="color:rgb(0,0,0);"name="hell_no">
The difference between a mobile gas water heater and a standard gas water heater is that a MH unit will use an outside air intake for combustion. That is the most important difference.
heater vent will not readjust to any position
No, each must be vented seperately.
There is no vent pipe on top of a hot water heater. Mobile home or not. You must be thinking of something else. The HW tank is only vented by a Pressure Relief Valve vented to the drain.