AO Smith Direct Vent Water Heaters
Review and Buying Tips

Review of the AO Smith direct vent water heaters from ProMax and manufactured housing series, including the features and specification.

AO Smith gas direct vent water heater

AO Smith manufacturer designs three types of the direct vent gas water heaters, all utilizing coaxial (pipe within the pipe) vent system. The models are found in several sizes which are in the range from 30-gal to 75 gallons, all powered by natural and LP gas. Direct vent system comes with the great advantage over power vent models, water heaters do not need electrical power for its work and are used in homes that might have an issue with the insufficient indoor ventilation or where the electricity can be provided for water heating. The only venting option these models offer is the horizontal layout through the outside wall.

ProMax Direct Vent

Venting

ProMax direct vent water heaters feature one pipe and dual channel closed vent system that gets the air from the outside atmosphere and at the same time removing the products of combustion safely out.

Intelligent control

Thanks to the built-in microprocessor, ProMax direct vent units are getting hot water with the temperatures that are controlled better and more accurate, resulting in the optimized performance and comfort.

Dip tube

Dip tube, as most of the water heaters from AO Smith, are part of the Dynaclean system that reduces the sediment and limescale deposits, by creating the turbulent water flow inside the heater's tank.

Gas control valve

The gas valve is self-powered, which means that no electricity is needed for its work, but it uses the thermopile to generate the power. The gas control also monitors the water heating process and indicates when there is a problem.

Gas combustion

Either using the natural gas or propane, the piezo igniter is used to light the pilot, and the Green Choice gas burner for gas combustion, with the reduced emission of NOx gases.

Models and specs

Models / Specs GDV 40
GDV 50
GDVT 50
GDV 75
Capacity
Gal
37 50 50 75
Gas input
BTU
38,000 42,000 50,000 55,000
FHR
GPH
73 87 88 131
Energy
factor
0.60 0.59 0.58 0.57
Recovery
rate
GPH
37 45 55 60
Max. vent
length
ft
80 80 80 80
Weight
lb
167 185 187 310

ProMax SL

AO Smith direct vent water heaters from SL series utilize the side mounted recirculating taps for the installation in residential homes and for combination space and potable water heating and systems that require a recirculation.

As the above models, ProMax SL direct vent water heaters use the coaxial type venting system with the closed combustion system, where the inside pipe is used as the exhaust and outer pipe to draw the fresh combustion air inside the unit.

SL models are equipped with the same features as the ProMax direct vent water heaters; intelligent control logic, self-powered electronic gas valve, Green Choice gas burner, Dynaclean diffuser dip tube...

Models and specs

Models / Specs GDVL 40
GDV 50L
GDV 75L
Capacity
Gal
40 50 75
Gas input
BTU
38,000 50,000 55,000
FHR
GPH
73 88 131
Energy
factor
0.60 0.58 0.57
Recovery
rate
GPH
37 55 60
Max. vent
length
ft
80 80 80
Weight
lb
167 185 310

ProMax Manufactured Housing

AO Smith direct vent water heaters for manufactured housing are designed with the bottom intake air vent and used to draw the fresh air for combustion from outside.

These models are equipped with the features that are the same as the above water heaters, but with one major difference, these can be used as the atmospheric units and with the right kit as the direct vent models.

Models and specs

Models / Specs FMD-30
FMD-40
FMD-50
Capacity
Gal
30 40 50
Gas input
BTU
30,000 32,000 48,000
FHR
GPH
54 64 77
Energy
factor
0.43 0.60 0.59
Recovery
rate
GPH
31 33 39
Max. vent
length
ft
30 30 30
Weight
lb
115 134 170

All the models that comply with the Energy Star requirements, such as the High EF and Ultra-low NOx series, provide more energy and money savings than the SL series, which doesn't comply. The above models are factory built to use natural gas, while propane models have the same specifications and warranty of 6 years.

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