Water HeatersResidential-Duty Commercial
A. O. Smith HDHE-50 4 Water Heater Manual
Setup, everyday use, maintenance and troubleshooting for the 49-gallon residential-duty commercial gas water heater, with verified specifications.
- UEF0.88
- Tank49 gal.
- First-hour rating118 gal.
- Est. yearly cost$288
About the A. O. Smith HDHE-50 4
A. O. Smith model HDHE-50 4 is a 49-gallon residential-duty commercial gas water heater that meets ENERGY STAR efficiency requirements.
It stores 49 gallons and has a first-hour rating of 118 gallons — the amount of hot water it can supply in one busy hour starting with a full tank. The DOE classifies it in the high usage draw pattern, so its efficiency rating assumes about 84 gallons of hot water a day.
Its UEF of 0.88 is far above the roughly 0.6 of a basic atmospheric gas tank; ratings this high come from condensing designs that extract heat from the exhaust, which is why they use plastic vent pipe and need a condensate drain. That UEF is higher than 16% of the 71 residential-duty commercial models in our database.
It fires at up to 100,000 Btu/h with a recovery efficiency of 97%; it is a power vent unit using 2 or 3 in. vent pipe.
Specifications
| Brand | A. O. Smith |
|---|---|
| Model number | HDHE-50 4** |
| Water heater type | Residential-Duty Commercial |
| Fuel / energy source | Natural gas or propane |
| Storage volume | 49 gal. |
| First-hour rating | 118 gal. |
| DOE draw pattern | High-Usage |
| Uniform Energy Factor (UEF) | 0.88 |
| Estimated annual natural gas use | 192 therms/yr |
| Estimated annual propane use | 210 gal./yr |
| Gas input rate | 100,000 Btu/h |
| Recovery efficiency | 97% |
| Maximum current | 5.0 A |
| Tank height | 55.7 in. |
| Tank diameter | 18.0 in. |
| Venting | Power vent |
| Vent pipe diameter | 2 or 3 in. |
| Connected / demand-response capable | No |
Safety information
- Set the water heater to about 120 °F (49 °C). Water at 140 °F can cause a serious burn in a few seconds; at 120 °F it takes several minutes. Homes with young children or older adults benefit from anti-scald valves at tubs and showers.
- The temperature and pressure (T&P) relief valve protects the tank from bursting. Never cap, plug or remove it, and keep its discharge pipe running full size to within about 6 in. of the floor or to an approved drain.
- Installation should be done by a licensed plumber (and electrician or gas fitter where required). Most jurisdictions require a permit.
- Install carbon monoxide alarms on every level of the home and near sleeping areas, and keep the vent and air-intake terminations clear of snow, leaves and nests.
- If you smell gas, do not operate switches or appliances; leave the building and call your gas utility or 911 from outside.
- Never store gasoline, solvents or other flammable products near the water heater.
- Where local code requires it (for example, in seismic zones), secure the tank to the wall with approved strapping.
Installation and first-time setup
Use this checklist when planning the installation of the A. O. Smith HDHE-50 4 and when reviewing the finished job with your installer.
- Venting
Install the vent system exactly as the manual specifies for power vent installation using 2 or 3 in. pipe. Powered venting needs a 120 V receptacle (maximum current 5.0 A), so the heater will not run during a power outage.
- Gas supply
Size the gas line for the 100,000 Btu/h input, with a shut-off valve and sediment trap, and leak-test every joint with an approved solution or detector.
- Condensate drain
Route condensate to a suitable drain or condensate pump, with a neutralizer if required.
- Drain pan and space
Install a drain pan where a leak could cause damage, and keep the clearances to combustibles and service access the manual lists. Plan for a tank about 55.7 in. tall and 18 in. in diameter.
- Plumbing connections
Use dielectric fittings where dissimilar metals meet, install a shut-off valve on the cold inlet, and pipe the relief valve discharge to an approved location. Add an expansion tank if the supply has a check valve or pressure-reducing valve.
- Fill and purge before start-up
Fill the tank completely and run a hot tap until water flows steadily, so no air remains, before turning on the gas and power. Then set the temperature and check every joint for leaks.
Using your water heater
Temperature and recovery
Set the thermostat to about 120 °F. With a first-hour rating of 118 gallons, it can handle several back-to-back showers plus laundry or dishwashing in a busy hour; if you regularly run short, spreading out heavy uses helps more than raising the temperature.
Use the vacation setting when you are away for several days. Because this model uses powered venting, it will not heat water during a power outage.
Saving hot water and energy
- Fix dripping hot-water taps promptly and use WaterSense showerheads and faucet aerators.
- Insulate the first several feet of hot and cold pipes at the heater.
- Wash laundry in cold water when possible.
Care and maintenance
| When | What to do |
|---|---|
| Every year | Test the T&P relief valve by lifting its lever briefly with a bucket under the discharge pipe; if it does not reseat and stop dripping, have it replaced. |
| Every year | Drain a few gallons from the tank drain valve, or flush it fully, to remove sediment — more often in hard-water areas. |
| Every 2–3 years | Have the anode rod inspected and replaced when it is heavily corroded; this is the main defense against tank corrosion. (Some models use a powered anode — follow the manual.) |
| Every year | Have the burner, powered vent, condensate drain and neutralizer inspected, and check vent joints for leaks. |
| Every month | Test carbon monoxide alarms. |
Troubleshooting
Check these common causes before calling for service.
| Problem | Possible cause | What to try |
|---|---|---|
| No hot water | No power to the vent blower; gas off; ignition lockout. | Check the 120 V outlet and breaker and the gas valve; consult the status codes in the manual. |
| Not enough hot water | Demand exceeds the first-hour rating; thermostat set low; sediment buildup. | Stagger heavy uses; check the setpoint; flush the tank. |
| Rumbling or popping sounds | Sediment on the tank bottom. | Flush the tank; in hard water consider a softener. |
| Rotten-egg smell in hot water | Bacteria reacting with the anode rod or water chemistry. | Flush the tank; a plumber can replace the anode with a different alloy or treat the water. |
| Relief valve dripping or discharging | Excess pressure from thermal expansion; failing valve; temperature set too high. | Have the pressure checked and an expansion tank added if needed; replace a faulty valve. Never plug it. |
Energy use and running costs
On natural gas, the A. O. Smith HDHE-50 4 is estimated to use 192 therms per year, about $288 a year at $1.50 per therm.
A basic gas storage water heater with a UEF of about 0.60 would burn roughly 282 therms for the same hot water — about $134 more per year.
On propane it is estimated to use about 210 gallons per year; multiply by your local propane price to estimate cost.
These estimates come from the DOE test, which assumes 84 gallons of hot water a day heated from 58 °F to 125 °F; your use will differ. The vent blower and controls also use a small amount of electricity, not included here.
Frequently asked questions
How much hot water does the A. O. Smith HDHE-50 4 provide?
It has a 49-gallon tank and a first-hour rating of 118 gallons, which is the best guide to how it handles a busy morning.
What is the UEF of the A. O. Smith HDHE-50 4?
Its Uniform Energy Factor is 0.88, measured in the DOE high usage draw pattern. Higher is better; compare UEF only between models in the same draw pattern.
How much does it cost to run the A. O. Smith HDHE-50 4?
About $288 a year on natural gas, based on its estimated 192 therms/yr at $1.50/therm. On propane it would use about 210 gallons a year.
What venting does the A. O. Smith HDHE-50 4 use?
It can be installed as a power vent unit with 2 or 3 in. vent pipe. Follow the installation manual for approved materials and maximum lengths.
Is the A. O. Smith HDHE-50 4 ENERGY STAR certified?
Yes. It appears on the ENERGY STAR certified water heater list, with a certification date of December 2025.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified water heaters dataset published by the U.S. Environmental Protection Agency (record certified December 11, 2025), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with A. O. Smith. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact A. O. Smith or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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