The fastest way to make your house water hotter is to turn up the thermostat on your water heater. Most units ship set to 120°F, and a simple adjustment can raise that to 140°F or higher in minutes. But if your thermostat is already turned up and the water still isn’t hot enough, the problem is likely something else entirely. Here’s how to diagnose and fix it.
Adjusting Your Water Heater Thermostat
On a gas water heater, the thermostat is a dial near the bottom of the tank. Some dials show specific temperatures, while others use labels like “Low,” “Medium,” “Hot,” and “Very Hot.” If yours uses labels, check the owner’s manual to find out what temperature each setting represents, because these vary by manufacturer. Turn the dial one setting higher, wait a couple of hours for the tank to fully reheat, then test the water at a faucet.
Electric water heaters have thermostats behind access panels on the side of the tank, usually one for the upper element and one for the lower. You’ll need to shut off the breaker, remove the panel covers, and use a flathead screwdriver to adjust the temperature dial on each thermostat. Set both to the same temperature. Replace the panels and restore power.
Tankless water heaters use a digital control panel. Many models, including popular Rheem units, ship with a factory default maximum of 120°F. You can override this limit through a button sequence to unlock temperatures up to 140°F. The exact steps vary by brand, so check your manual or look up your specific model number.
How High Is Safe?
The U.S. Consumer Product Safety Commission recommends keeping residential water heaters at 120°F to reduce scald risk. The numbers behind that recommendation are worth knowing: exposure to 140°F water causes third-degree burns in six seconds, and 150°F water does the same in just two seconds. Even at 120°F, a five-minute exposure can cause third-degree burns.
If you have young children, elderly family members, or anyone with reduced sensation in their skin, 120°F is the safest ceiling. But there are legitimate reasons to store water hotter than that. The bacteria that causes Legionnaires’ disease thrives in water between 77°F and 113°F and can grow at temperatures as low as 68°F. The CDC recommends storing hot water above 140°F to eliminate this risk. The solution to this tension between scald safety and bacteria control is a mixing valve, covered below.
Install a Thermostatic Mixing Valve
A thermostatic mixing valve lets you store water at a high temperature (140°F or above to kill bacteria) while delivering it to your faucets at a safer temperature (around 120°F). The valve automatically blends cold water into the hot water line right before it reaches your fixtures. If the cold supply fluctuates, the valve adjusts in real time, so the output temperature stays constant.
This is increasingly standard practice worldwide: store at 140°F, deliver at or below 120°F. A plumber can install a single mixing valve at the water heater outlet to protect the whole house, or you can add point-of-use valves near individual fixtures like showers and sinks. As a bonus, because the stored water is hotter, each gallon goes further when mixed with cold, effectively increasing your hot water supply.
Flush Sediment From the Tank
If your water heater is set to the right temperature but the water coming out feels lukewarm, sediment buildup is a common culprit. Minerals in your water settle at the bottom of the tank over time, forming a layer of scale between the heating element (or gas burner) and the water itself. This layer acts as insulation, forcing your heater to work harder while delivering less heat to the actual water.
Flushing the tank is straightforward. Turn off the heater, connect a garden hose to the drain valve at the bottom of the tank, and run the water into a bucket or floor drain until it comes out clear. Doing this once a year keeps sediment from accumulating enough to affect performance. If you live in an area with hard water, every six months is better.
Check for a Broken Dip Tube
The dip tube is a plastic pipe inside your tank that directs incoming cold water to the bottom, where the heating element is. When the dip tube cracks, breaks, or disintegrates, cold water enters near the top of the tank and mixes directly with the hot water sitting there. The result is water that’s consistently lukewarm no matter how high you set the thermostat.
The telltale sign is water temperature that swings from hot to warm unusually fast, or water that never gets fully hot even after a long recovery period. Small white plastic flecks in your faucet aerators or showerhead are another giveaway, as they’re pieces of the deteriorating tube. Dip tubes are inexpensive parts, but replacing one involves removing the cold water inlet fitting on top of the tank, so most people hire a plumber for this repair.
When the Problem Is Distance, Not Temperature
Sometimes the water at the heater is plenty hot, but by the time it reaches a distant bathroom or kitchen, it’s cooled significantly in the pipes. You also end up waiting a long time for hot water to arrive, running cold water down the drain in the meantime.
A hot water recirculating pump solves this. It keeps hot water slowly moving through your pipes so it’s available almost instantly at every fixture. The pump pulls cooled water from the hot water lines and sends it back to the bottom of the tank for reheating. Installation requires a bypass path somewhere in your plumbing, which may mean opening a wall, though some systems use the cold water line as the return path to simplify installation. Timer or sensor-equipped models only run during peak usage hours, which limits the energy cost.
For a single fixture that’s far from the heater, a point-of-use tankless water heater mounted under the sink or near the shower is another option. These small electric units heat water on demand right where you need it, bypassing the distance problem entirely.
Insulate Exposed Pipes
Hot water loses heat as it travels through uninsulated pipes, especially those running through unheated spaces like basements, crawl spaces, or garages. Foam pipe insulation sleeves are inexpensive, require no tools beyond a utility knife, and can reduce heat loss enough to raise the temperature at distant taps by several degrees. Focus on the first six to ten feet of pipe leaving the water heater and any runs through cold areas. This also shortens the wait time for hot water and reduces the energy your heater uses to maintain temperature.