The Hidden Impact of Water Temperature on Energy Costs

Heating water accounts for roughly 18 percent of a typical home’s energy use, making it the second-largest energy expense after space heating and cooling. A significant portion of that energy is consumed just to maintain a high water temperature, even when no hot water is being drawn. Most water heaters arrive from the factory preset to 140°F (60°C)—a setting that prioritizes rapid recovery and bacterial control but often far exceeds what is needed for daily tasks. By simply lowering your water heater’s thermostat, you can reduce standby heat loss, cut energy consumption, and lower your monthly utility bill without sacrificing comfort.

The relationship between water temperature and energy consumption is straightforward: the hotter the water, the more energy required to heat it and the greater the heat loss through the tank walls and pipes. A 10°F reduction in water temperature can save 3 to 5 percent on water heating costs, according to the U.S. Department of Energy—an achievable adjustment that adds up to meaningful savings over time.

Understanding Your Water Heater’s Default Settings

Manufacturers typically set water heaters to 140°F for two primary reasons. First, 140°F is the temperature at which the bacteria Legionella pneumophila is killed relatively quickly, reducing the risk of Legionnaires’ disease. Second, a higher temperature ensures that a standard 40- or 50-gallon tank can deliver enough hot water for showers, laundry, and dishwashing without running out. However, this default setting was never tailored to your household’s specific needs or energy-saving goals.

The downside of a 140°F setting is significant. Water at this temperature can cause third-degree burns in as little as five seconds, posing a serious scalding risk for children, elderly individuals, and anyone with reduced mobility. Additionally, the higher temperature accelerates mineral buildup inside the tank (scale), shortening the lifespan of your water heater and reducing its efficiency. The energy wasted in standby heat loss also increases because the greater temperature difference between the tank and its surroundings causes more heat to escape.

Lowering the temperature even by 10 degrees reduces the rate of heat loss, slows scale accumulation, and makes the system safer—all while still providing ample hot water for most households.

Finding the Optimal Water Temperature for Your Home

The sweet spot for most homes lies between 120°F and 130°F. The U.S. Department of Energy recommends 120°F as the default setting for energy efficiency and safety. At this temperature, a water heater still kills most harmful bacteria (though not as quickly as at 140°F), and the risk of scalding drops dramatically—a child would need about 10 minutes of exposure to suffer a burn at 120°F versus five seconds at 140°F.

However, a flat recommendation of 120°F may not suit every household. Consider these factors:

  • Dishwasher performance – Some older dishwashers require incoming water at 130–140°F to properly dissolve detergent and sanitize dishes. Newer ENERGY STAR models have internal heating elements and work fine with 120°F water. Check your dishwasher’s manual.
  • Number of occupants – Households with three or more people may find that a 50-gallon tank set at 120°F struggles to keep up during back-to-back showers. Raising the temperature slightly (to 125–130°F) helps stretch the hot water supply by mixing with more cold water at the faucet.
  • Health concerns – If someone in your home has a compromised immune system or chronic respiratory condition, your doctor may recommend maintaining 130°F or higher to reduce bacterial risk. In such cases, install anti-scald devices or thermostatic mixing valves at points of use to prevent burns.
  • Children and elderly – For homes with young children or older adults, keeping the temperature at 120°F or lower is strongly advised. Anti-scald valves provide an extra layer of protection even at cooler settings.

How to Determine the Right Temperature for Your Situation

Start by assessing your household’s hot water demand. A simple test: time how long you can take a comfortable shower before the water starts cooling. If you run out of hot water regularly, your current setting may be too low, or your tank may be undersized. If you rarely exhaust the tank, you can likely lower the temperature. Also, measure the actual water temperature at the tap (see instructions below) rather than relying on the dial markings, which are often inaccurate.

Step-by-Step Guide to Adjusting Your Water Heater

Adjusting your water heater is a simple DIY task, but the method varies by type. Always prioritize safety: turn off the power (for electric heaters) or set the gas valve to pilot (for gas heaters) before opening any access panels. Use a thermometer to confirm the final temperature reach the desired level.

Adjusting an Electric Water Heater

  1. Turn off the circuit breaker supplying power to the water heater.
  2. Remove the access panel(s) covering the thermostat(s). Electric water heaters typically have two thermostats—upper and lower—that must be set to the same temperature.
  3. Use a flathead screwdriver to turn the dial to your desired setting. Most dials have marks like “A, B, C” or temperature indications. If unmarked, a good starting point is around 120°F (approximately the “C” setting on some brands).
  4. Replace the insulation and access panels, then turn the power back on.
  5. Allow the tank to heat for at least one hour, then test the water temperature at a nearby faucet. Run hot water for three minutes, then fill a glass and use a candy or instant-read thermometer. Adjust again if needed.

Adjusting a Gas Water Heater

  1. Turn the gas control valve to the “Pilot” position. On most models, the thermostat dial is part of the gas valve.
  2. Read the current temperature setting (often marked with numbers 1–5 or “Low, Hot, A, B, C”). Turn the dial to the desired level. For 120°F, start at a “Low” or “1” setting and verify with a thermometer.
  3. Turn the gas valve back to “On” and ensure the pilot light relights (some models have electronic ignition and will light automatically).
  4. Wait one hour, then test the water temperature at a faucet as described above. Gas heaters often need fine-tuning because the dial markings are less precise.

Adjusting a Tankless Water Heater

Tankless heaters typically have a digital display or a set of buttons on the control panel. Follow the manufacturer’s instructions to adjust the outlet temperature. Many models allow you to set the temperature in 1-degree increments. Start at 120°F and increment up only if you run out of hot water during heavy use. Note that tankless heaters—especially gas-powered ones—can take a few seconds to reach set temperature, so test after a minute of flow.

Additional Energy-Saving Strategies Beyond Temperature Adjustment

Lowering the thermostat is the single most effective step, but you can amplify your savings with these complementary measures.

Insulate Your Water Heater and Pipes

An insulation blanket for your storage tank can reduce standby heat loss by 25 to 45 percent, paying for itself in under a year. Be careful not to cover the thermostat access panel or the burner area on gas heaters. Insulating the first six feet of hot water pipes with foam pipe sleeves also reduces heat loss as water travels to your fixtures. This is especially beneficial in unheated basements or crawl spaces.

Fix Leaks Promptly

A single dripping hot water faucet can waste hundreds of gallons per year, and the energy used to heat that water is lost. Repairing leaks is a free way to reduce both water and energy bills. Check faucets, showerheads, and pipe joints regularly.

Install Low-Flow Fixtures

Low-flow showerheads (2.0 gallons per minute or less) and faucet aerators can cut hot water consumption by 30 to 50 percent without noticeable pressure reduction. The less hot water you use, the less your water heater has to work. Many utilities offer rebates for water-saving fixtures.

Consider Temperature Setbacks

If your water heater is located in a conditioned space, a vacation or “away” mode can drop the temperature to around 100°F while you are gone for more than a few days. Programmable water heater controllers are available, or you can simply turn the dial down manually and bring it back up before you return. Never turn the heater completely off, as the tank may develop odors or corrosion.

Upgrade to an Energy-Efficient Water Heater

If your current water heater is more than 10 years old, replacement with a modern high-efficiency model can slash energy use. Heat pump water heaters (hybrids) are the most efficient for most climates, using 60 to 70 percent less electricity than standard electric tanks. Gas condensing water heaters offer similar savings over non-condensing models. Tankless heaters eliminate standby losses entirely. Always check ENERGY STAR certified models and look for rebates through DSIRE (Database of State Incentives for Renewables & Efficiency).

The Bottom Line: How Much Can You Save?

The U.S. Department of Energy estimates that lowering your water heater temperature from 140°F to 120°F can save homeowners between $30 and $60 per year on energy bills, depending on local energy rates and usage patterns. Combined with insulation and low-flow fixtures, total savings can exceed $100 annually. Over the typical 12-year lifespan of a water heater, that’s more than $1,000 in avoided energy costs—plus reduced risk of scalds and longer appliance life due to less scale buildup.

For a precise estimate tailored to your home, use the Energy Saver water heating calculator from the Department of Energy.

Frequently Asked Questions

Will 120°F water kill Legionella bacteria?

Yes, but more slowly than at higher temperatures. At 120°F, Legionella can survive for several hours, whereas at 140°F it dies within minutes. For households with healthy members, the risk is very low if you use the water daily and do not store water for long periods. If you are concerned, raise the temperature to 130°F and install anti-scald valves. The CDC recommends maintaining water heaters at 120°F for energy efficiency but suggests higher temperatures in high-risk settings like hospitals.

Can I lower the temperature if I have a dishwasher?

Yes, as long as your dishwasher has a built-in booster heater (most models manufactured after 2010 do). Check the owner’s manual. If it does not, you may need to keep the water heater at 130–140°F for proper cleaning. In that case, install a tempering valve at the kitchen sink to avoid scalding.

Is it safe to adjust my water heater myself?

Yes, for most electric and gas models, as long as you follow safety precautions. Always turn off the power or gas before accessing thermostats. If you are uncomfortable working with electricity or gas, hire a licensed plumber or HVAC technician. Tankless heaters with digital controls are generally easy to adjust via the interface.

Conclusion

Your water heater’s temperature setting is a simple lever with disproportionate impact on your energy bills, safety, and appliance longevity. By dialing it down to between 120°F and 130°F, you can save money, reduce scalding risks, and extend the life of your equipment. Combine this adjustment with insulation, leak repair, and low-flow fixtures for maximum effect. Testing your water temperature at the tap and verifying the setting once or twice a year ensures your system remains optimized as seasons and occupancy change. Start by turning down your thermostat today—the savings will show up on your next bill.