Both gas water heater and gas combination boiler can produce hot water.  What on earth are the difference between the two?

As we all know, gas water heater is used to supply domestic hot water(DHW) for household, while gas combinationboilercan supply hot waternot onlyforspace heating but also DHW.  In China, these two are subject to different standards. For gas water heater, standard code is GB 6932 while for wall hung gas combination boiler, it is GB25034.

Besides, they differ in the way of describing hot water production capability. The hot water production capacity of the gas water heater refers to the hot water production per minute under the condition of a temperature rise of 25K. For combination boiler, as it takes into consideration actual operation conditions, thus it indicates hot water per min at 30K rise. Seemingly with the samepower, gas water heater can produce more hot water than gas combination boiler. But the fact is there is hardly difference between the two. Only computing method of them varies.

Due to inconsistent operating conditions, gas water heaters are typically used for shorter periods of time and in intervals. Gas combination boiler needs to be used continuously for a long time, so the requirements for the safety performance of the wall-hung boiler and the gas water heater are different.

The flue used by the water heater is a single pipe. Generally, the unit is installed indoors, the  air for combustion is taken indoors, and the exhaust gas is discharged to the outdoors through the flue. Because the gas water heater consumes indoor air during the combustion process, the gas water heater should not be used continuously for a long time. The flue of the wall-hung boiler is a coaxial double-pipe, the air required for combustion is taken from the outdoors, and the exhaust gas is also discharged to the outdoors, so there is no need to consume indoor air. Thus,from the perspective of safety, the wall-hung boiler is better than the gas water heater.

In addition, generally gas water heaters are not equipped with anti-freeze protection function. Only outdoor units are equipped with electric heating to prevent freezing. Wall-hung boilers are designed withdouble antifreeze function. In winter, when the wall-hung boiler detects that the ambient temperature drops (generally to 7-8°C), the water pump of the wall-hung boiler will automatically start running to drive the water system to circulate and prevent the system from freezing. When it detects that the temperature further drops to the freezing point or the temperature is lower than 5-6°C, the wall-hung boilerwould automatically ignite,start operation, and heat the water of the system to a certain temperature (15-30°C),so as to keepthe entire system from freezing.

Although gas wall-hung boilers and water heaters both generate hot water, gas-fired wall-hung boilers have higher requirements on the amount of hot water. To meet both heating and DHW needs, the manufacturing process requirements for wall-hung boilers are even higher. The power of gas water heaters is generally around 16-20kw. In order to achieve greater hot water volume, the power of gas wall-hung boilers is much higher than that of gas water heaters, generally from 24kW to 40kW.

Finally, their cost is different. Because the gas wall-hung boiler needs to meet the heating demand, it must realize the hot water circulation, which requires that there must be a circulation pump inside the gas wall-hung boiler.This part alone drives upits cost. Based on the above, the price of gas wall-hung boilers is generally more higher than that of gas water heaters. However, some recent models of gas water heaer, like zero cold water gas heaters are also equipped with water pump. If this become trendy, the difference between the twowouldgradually narrow.