Hayward H150FDN Universal H Series Low NOx 150 000 BTU Natural Gas Residential Pool and Spa Heater Common QuestionsWhat are the dimensions of the unit? W3h200fdn universal h-series, low nox, 200k btu, natrual gas, pool & spa heater high and low voltage connections are easy and convenient with left and right side junction boxes. The W3H200FDN is equipped with a cupro-nickel heat exchanger to make it salt water capable.