For homes with more than 3 bathrooms, large-volume demands for hot water, or hot water circulating systems, you should choose the GT-199 heavy-duty series water heater. In some applications, up to 20 heavy-duty tankless water heaters are linked together in a manifold configuration to meet the higher volume demands for continuous hot water. Unit Size 19,000 - 199,000 BTU's, specify Natural or Propane Gas.