This division (relating to Water Heaters, Small Boilers, and Process Heaters) does not apply to:(1) units using a fuel other than natural gas;(2) units used in recreational vehicles;(3) Type 0 units, or Type 1 or 2 units at single-family residences, used exclusively to heat swimming pools and hot tubs;(4) units manufactured in Texas for shipment and use outside of Texas; and(5) units that do not comply with the nitrogen oxides specifications in §117.3205 of this title (relating to Emission Specifications) that are sold, supplied, or offered for sale in Texas, provided that the manufacturer or distributor can demonstrate that the units are intended for shipment and use outside of Texas, and that the manufacturer or distributor has taken reasonable, prudent precautions to assure that the units are not distributed for sale in Texas. This paragraph does not apply to units that are sold, supplied, or offered for sale by any person to retail outlets in Texas.