State Tankless Water Heaters 
Review and Buying Tips

Review of the best condensing and non-condensing State tankless water heaters. Find the top models with superior high thermal efficiency and flow rate. Check out which of the tankless models are saving you the most money and why?

State tankless water heaters are built for an efficient and environment-friendly potable water heating in residential and commercial applications - directly or indirectly, including hydronic heating, recirculation, and storage tank usage. All of the on-demand models are Energy Star approved, which means that the energy factor is 0.82 or higher and with the gas input of up to 199,900 BTU. Those models that have the most advanced features, highest EF factor and savings are known as condensing. Other models are non-condensing.

Model review

State tankless water heaters

All residential non-condensing tankless water heaters from State can be grouped into three categories: 110, 310 and 510.

State tankless water heaters from the 110 series are the smallest units, and since the capacity of 6.6 GPM is enough for one to two showers, these are ideal for apartments, condos and smaller houses. Water heaters are available as indoor - GTS-110-NI, outdoor - GTS-110-NE and direct vent models.

310 series comes with the direct vent, indoor and outdoor models, including the models with the ultra-low NOx, all having the maximum water flow of 8 GPM, making it great for two and three showers.

State 510 series of tankless water heaters have the highest water flow rate of 10 GPM, which is excellent for three to four showers working simultaneously, but depending on the region as the groundwater temperature varies. The 510 series is also found in three types; direct vent, indoor and outdoor, and plus with the ultra-low NOx emission.

Keep in mind that the warranty for all models is 15 years on the heat exchangers and 5 years on other elements. Proper plumbing installation, for example, maintenance and winterizing are just some of the factors that need to be taken care properly for the tankless longevity. The reason for the longer warranty on the heat exchanger is due to its commercial-grade copper heat exchanger that can sustain higher loads and stress.

Comparing 510, 310 and 110 series

State GTS-510C-NI models are the power direct vent models that utilize the concentric vent system for the air intake and exhaust and are used only in indoor applications. The Eco-friendly gas burner is capable to modulate its power from 15,000 to the highest 199,000 BTU, resulting in the efficient and clean combustion and ultra-Low NOx emission. These can be used in residential and commercial applications.

A similar model, but using less power is the GTS-310C-NI model.

State GTS-510U-I is another ultra-low NOx model that uses the two vent pipes in direct venting setup, designed for indoor use only. Like the above model, GTS-510U-I is also equipped with the digital display built into the front of the unit for more convenience. GTS-510U-I and its outdoor counterpart GTS-510U-E utilize the heat exchanger that has thicker walls than the one found on other models making it great for heavy residential usage and even for light commercial applications.

These models come with the higher capacity, but if more hot water is needed, up to four of these models can be linked by using the Easy-Link system, or Multi-Link system which connects up to 20 units.

Similar models but with less power are GTS-310U-I and GTS-110U-I as the direct indoor models and GTS-310U-E and GTS-110U-E as the ventless outdoor units.

Other two models from 510 group; GTS-510-NI and GTS-510-NE are the power vent indoor and outdoor models both having the commercial-grade heat exchanger for added protection and long-lasting operation. Remote control is included as the standard feature. While they have the same maximum gas input as the above 510 models, these units can modulate the power to the minimum of around 11,000 BTU. Up to 4 units can be combined through the Easy-Link System, so more hot water is available for demanding homes.

Similar models, but with less power are an indoor model GTS-310NI and the outdoor GTS-310NE both utilizing one heat exchanger made of the copper alloy HRS35.

310 and 110 series are designed only for residential applications, not commercial as the 510 series.

Similar: Takagi and AO Smith

Top features


One of the neat features that is present on the newer State tankless water heaters is a digital controller, which is used not only to monitor the temperature but to get a notification when there is a problem with the heater. The LCD display shows the current temperature of the outgoing hot water and when the problem occurs, the error codes flashes, followed by the audio alarm.

Underneath the display, there are several buttons, which help you turn the unit ON or OFF, change the temperature, get the information about the water temperature and flow rate and set the time.

Heat exchangers

Condensing tankless water heaters are the most advanced on the market. State condensing models have two heat exchangers, the main one which is usually made of copper, where most of the heat transfer occurs, and the second one, stainless steel, which is used to increase the temperature of the incoming cold water. Thanks to the SS material the corrosion resistance is greater.

Non-condensing models have one heat exchanger, which is made of copper and these models are cheaper to buy, but condensing are better performing; the energy factor is 0.91, vs. 0.82. Some models are equipped with the commercial-grade heat exchanger providing better protection and less wear and tear in years to come.


Non-condensing water heaters must use Category III Stainless Steel venting system while condensing, due to the lower temperature of the exhaust gases, can use PVC vents. The great thing about the tankless water heaters is flexibility when installing the vents since they can run horizontally or vertically. As the units use the power vent for directing gases out, the maximum length is up to 50 feet. Due to the closed combustion, direct vent with the concentric vent is also an option.


Every tankless unit from this manufacturer is equipped with several safety features such as the air-fuel ratio or AFR sensor which ensures proper mixture of air and gas and less emission and better efficiency; freeze protection and other sensors and switches protecting the unit from high temperatures and overheating.

State tankless water heaters are an ideal solution for those who are looking for on-demand water heating, to save floor space and want a peace of mind when referring to the capacity. State heaters are similar to tankless models from AO Smith and Takagi, and the great thing is the variety and service network. With several safety features, such as the built-in freeze protection and overheat sensor or flame detection unit, and users are well protected. State heaters are also environment-friendly as their burners are low NOx burners. Read more about condensing tankless water heaters from State.


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