1.Natural exhaust – without baffle designed (chimney) for the exhaust of gas burned but only through natural dragging.

2.Flue exhaust –  an internal baffle designed (chimney) for the exhaust of gas burned through natural dragging.

3.Forced exhaust – The exhaust of burned gas is performed by an internal fan. It facilitates the exhaust system installation due to the reduced chimney diameter, making it safer.

4.Balanced exhaust - The system with double exhaust pipe,fresh air from outside and gas forced to outside also.this heater can be installed inside bathroom which is the most safety gas water heater.

5.Forced exhaust or balanced exhaust with Constant Temperature Controlled –

In normal gas water heater,the temperature of outlet water will be up or down as soon as the water flow changed at any time.in specific time,the gas flow is fixed by knob,at the same time,some people need the water from same pipe which connected with gas water heater.the water flow will be smaller.but gas flow is the same.so the temperature will be hotter of outlet water.
Here The gas water heater at constant temperature technology which with proportional valve inside adjusted automatic between water flow and gas flow to keep the water temperature constant of outlet water for product.for example,you set the target temperature 42C as soon as you start the heater,you can get 42C all the time of outlet water from the unit.it is another style of life.just relax and enjoy the life.