Its not the water heater that causes the smell, its your water. Are you sure it was installed with 3/4 cold and hot water lines (required by rinnai)? Did the person who installed it bypass the filtration system with the cold line? You get the odor as you aerate the water at the tap. Your other water heater doesn't have the velosity that the rinnai puts out as the coil is only 3/8 which causes the water to flow through faster I.E airation is greater at the tap therefore you smell it more but the problem still remains even in your old water heater. Its in your water not the heater.