The National Fuel Gas Code NFPA 54 allows all Booster Water Heaters to vent into the room provided that certain overall conditions exist. This is explained in the following excerpt: EXCERPT FROM ANSIZ223.1/NFPA 54 7.2.1 Connection To Venting Systems. Excerpt as permitted in 7.2.2 through 7.2.6, all gas utilization equipment shall be connected to venting systems. 7.2.2 Equipment Not Required To Be Vented. A single booster-type [automatic instantaneous] water heater, when designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the equipment is installed, with the draft hood in place and unaltered, if a draft hood is required in a commercial kitchen having a mechanical exhaust system.

Where installed in this manner, the draft hood shall not be less than 36" (91 cm) vertically and 6" (15 cm) horizontally from any surface other than the equipment. Where any or all of this equipment is installed so the aggregate input rating exceeds 20 BTU per hour per cubic foot (207 watts per cubic m) of room space in which it is installed, one or more shall be provided with venting systems or other approved means for removing the vent gases to the outside atmosphere so the aggregate input rating of the remaining unvented equipment does not exceed the 20 BTU per hour per cubic foot (207 watts per cubic m) figure. Where the room or space in which the equipment is installed is directly connected to another room or space by a doorway, archway, or other opening of comparable size that cannot be closed, the volume of adjacent room or space shall be permitted to be included in the calculation.