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A peerless boiler to the left and a gas water heater to the right.
I see 3 problems with this picture. first and potentially most dangerous is the flexible gas tubing going to the water heater on the left, this flexible gas line has been recalled because it develops small pin holes and gas leaks out, very dangerous, the relief valve in the background is not extended far enough down towards the ground and can cause someone to be burned if it goes off.
Soot coming out around the gauge is a possible carbon monoxide leak. Have your equipment serviced by a real plumbing and heating contractor every year.