1. According to the type of gas, it can be divided into artificial gas water heater, natural gas water heater, liquefied petroleum gas water heater and biogas water heater. Water heaters of different gas types cannot be used universally. 

2. According to the control method of water heater outlet water, it can be divided into pre-standard and post-type water heaters. The front-mounted water heater uses the water inlet valve of the water heater to control the hot water flow of the water heater. The structure is simple, but the use is inconvenient; the post-type water heater uses the water outlet valve of the water heater to control the hot water flow of the water heater, and the structure is complicated, but It is more convenient to use. 

3. According to the water supply pressure, it can be divided into low pressure, medium pressure and high pressure water heaters.  

4. According to the water heater exhaust method, it can be divided into three types: open flue direct-discharge) (water heater, flue water heater and balanced water heater. 

 1) Open flue (direct-discharge) water heater: The air required for combustion in the direct-discharge type water heater is taken from the indoor, and the exhaust gas after combustion is directly discharged into the room. The safety is the worst. The relevant state departments have banned production and sales, and should be eliminated as soon as possible. ;  

2) Flue-type water heater: The flue-type water heater is an improvement of the open flue type water heater. An anti-winding exhaust hood and a smoke exhaust system are added to the upper part of the original straight-line structure. The main feature of the flue-type water heater is that the flue gas is discharged to the outside through the flue, which solves the problem of indoor air pollution to a certain extent. Compared with the direct exhaust of the open flue water heater, this is the safety technology of the gas water heater. progress. However, since the combustion air required for such water heaters is still taken from the room, the combustion intensity is low, the water heater is bulky, and problems in installation and use cause the water heater to still have many safety hazards. Therefore, from the perspective of ensuring user safety and environmental protection, flue-type water heaters will gradually withdraw from the market in the future. 

 3) Forced exhaust gas water heater: The main cause of safety accidents in gas water heaters is indoor air pollution. To avoid carbon monoxide poisoning accidents in the flue gas, the fundamental measure is to discharge the flue gas to the outside to keep the indoor air clean and hygienic. The forced exhaust type water heater discharges the combustion flue gas out of the room by forced exhaust or forced air blowing. The flue-type water heater uses the natural smoke exhaust method to discharge the flue gas to the outside, which is better than the open flue type water heater compared with the use safety. However, the flue-type water heaters have high requirements for the installation conditions of the flue, and the apartment houses in general cities are difficult to meet. The safety performance of the forced-discharge water heater is more perfect and the installation is relatively simple. Forced exhaust water heaters have two typical structures: exhaust and blast.