A.O. Smith® ATI-540H Tankless Water Heater Reviews

A.O. Smith® ATI-540H Review


The ATI-540H from A.O. Smith offers some great features but falls short when comparing other tankless water heaters we have reviewed. The unit we got to take for a test drive is rated at 199,000 Max BTU with a flow rate of 10 GPM. At 10 PGM we highly doubt you will ever run out of hot water. This is the largest residential unit that they offer.

The AT line comes in an indoor (ATI prefix) and outdoor (ATO prefix) option, as well as a natural gas or liquid propane (LP) options. The 240 line is rated for max BTU of 160,000 and 6.6 max GPM. And the 340 line is rated for 180,000 BTU and 8.0 GPM.

The ATI-540 is ideal for a large family with 3 showers.


What we liked about the A.O. Smith® ATI-540H

1. Out of the box the temperature range is from 100° F-185° F, Unlike other models you don’t have to adjust dip switches to get to the higher temperatures.

2. The size and weight is real of this tankless water heater is tiny in comparison to its competitors. It weighs in a on 66 lbs. While most comparable water heaters are 80 lbs. This makes it much easier to install and can be done by one person

3. This unit has a energy factor (EF) of 0.95, one of the highest in the class.

4. The primary heat exchanger is made with HR35 cooper. We are not metallurgist, but we did some checking and the HR35 cooper is a higher grade cooper then what A.O. Smith® competitors are using.

5. The secondary heat exchanger is constructed out of 316L stainless Steel.

6. Incase you want to convert your home to a Bed & Breakfast the unit rated for commercial applications

7. We really love the metal vent collars. These lets you connect the PVC venting to the tankless unit with out glue. This is great! If the unit ever needs to be repaired or replaced, you don’t have to cut the PVC.

8. Direct electronic ignition (no standing pilot lights)


What we didn’t liked about the A.O. Smith® ATI-540H

 1. The top clearance was 12” , which might limit instaltation options.

2. There was no remote control included, its optional.

3. If you are required to vent for make up air, you will need a 2nd penetration into the building.

4. The 185° F max temperature. We mentioned this as a like, but if you have small children this could be a hazard.


Safety Features

Air- Fuel Ratio Sensor

Exhaust & Water Temperature

Overheat Cut-off fuse.


A.O. Smith® ATI-540H Specs:

  • Min Gas Consumption Btu/h – 15,000
  • Max Gas Consumption Btu/h – 199,000
  • Water Capacity GPM Max – 10.0
  • TemperatureRange (With Include MC-91-2US)) – 100 ° to 185 °
  • Electrtical Consumption (normal) – 42 Watts
  • Electrtical Consumption (stand-by) – 2 Watts
  • Gas Supply Connection – 3/4 inch MNPT
  • Cold Water Input Connection – 3/4 inch MNPT
  • Hot Water Input Connection – 3/4 inch MNPT
  • Weight – 66 lbs
  • Energy Star
  • 15 year limited warranty