AO Smith Effex Water Heaters

See how AO Smith Effex water heaters, GAHH-40 and GAHH-50, are, thanks to its superior design and advanced features, among the most energy efficient atmospheric gas water heaters on the market today. This review will help you decide to buy the right model.

Model review

AO Smith Effex

Effex series features two models for residential water heating: GAHH-40 as a 40-gallon and GAHH-50 as a 50-gallon water heater, both models designed to use natural gas and generate 40,000 Btu/hr, which is sufficient for heating water in 2-3 bath homes. The high value of the energy factor, which is 0.70, makes these units to comply with the Energy Star standards that require the energy factor of minimum 0.67.

The difference between these two water heaters is not only in their size, weight, and capacity, but First Hour Delivery: 70 GPH for the 40-gallon model GAHH-40 and 81 GPH for the 50-gallon model GAHH-50. Recovery rate at 90 F rise is the same and is 43 gallons per hour, and they can be used to the maximum elevation of 10,100 ft. above the sea level.

Both 40 and 50-gallon Effex models come with the standard 6-year warranty for the water heater tank and parts.

Great features on AO Smith Effex

AO Smith Effex water heaters use the pressurized combustion chamber where the advanced air intake blower distributes an optimum mixture of air and gas for the high performance.

As the Effex is an atmospheric gas water heater but fan assisted, the pressure created inside the combustion chamber forces the exhaust gases through the flue and out. The patented air intake system and pressurized environment help the heater to extract more heat from the flue gases while it passes through.

This is what allows Effex water heaters to offer high efficiency and performance where more heat is transferred to the water, and less energy is lost. Effex energy factor of 0.70 is one of the highest for tank-type gas water heaters.


Effex GAHH-40 and GAHH-50 are not using a standing pilot as the majority of the conventional gas water heaters, they are using much better electronic ignition that is known as hot surface ignition.

Anode rod

Another great improvement in Effex series of tank-type water heaters is that AO Smith removed the standard type anode rod, which deteriorates during the time. Now, AO Smith Effex series uses powered anode rod that shows great results in protecting the tank from rust while providing an excellent performance in all water conditions. This powered anode rod is a permanent design so it doesn't need replacement as long as the rod is not damaged.

Dip tube

DynaClean diffuser dip tube is still present as on most of the AO Smith gas water heaters and what it does is that it reduces the lime and sediment buildup inside the tank, by creating the turbulent water flow.


The gas burner is still "Green Choice", an Eco-friendly element that helps in reducing the NOx emission by 33%. Both models are FVIR compliant, they are designed according to the Flammable Vapor Ignition Resistant standards.

LCD display

LCD display is a neat feature, not often found on conventional tank-type heaters and it allows you to check and set the temperature, while the unit problems are presented through the diagnostic codes.

Installing AO Smith Effex is as easy as the conventional type; it can use existing venting connections where the vent size is 3 and 4", making it great for replacements.

Since the Effex is a relatively new product, there are not many online reviews. Those that I have found were mainly positive. One of the users praised the feature which includes the vacation mode which helps in reducing the fuel consumption. Other positives were related to the high efficiency and recovery. One of the negatives that were often mentioned was the noise (not too loud though) made by the air injector.


AO Smith Effex water heaters are coming from North America’s leading manufacturer of residential and commercial water heaters. Effex offers superior design, and it provides one of the highest energy efficiencies in water heating industry. With the superior heat transfer, Effex water heater gives the maximum performances and savings up to 25% when comparing to the conventional tank-type gas water heaters. This is why this is a great option for those who are replacing the old inefficient water heater.

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