Bryan Steam'sflexible water tube boilers feature ultra low Nox boiler/burner design and use the latest metal fiber burner technology combined with air-fuel ratio control and a PID Controller to provide a four to one turndown ratio. The Bryan RV Series boiler with the revolutionary “Rapid Mix” combination gas/oil Gordon-Piatt forced draft burner is capable of achieving ultra low Nox with gas firing sub 9 PPM and reduced Nox on oil.