Return to Water Heater Article Index


Let the Natural Handyman take the mystery out of adjusting your water heater

There's nothing like a hot shower to wash away the worries of the day. And despite the proliferation of low-temperature detergents, hot or warm water really does clean clothes better!

But you can have too much of a good thing. That storage tank in your basement... the good old water heater... can be a real energy glutton. Lowering the temperature even a little can bring you big energy savings... from 3% to 5% for every 10 degrees!

Each type of water heater has a different adjustment method. The descriptions below will apply to most heaters. If your water heater is significantly different from the ones depicted here, we suggest you obtain a manual from the manufacturer.

First things first... test your water temperature

You don't need a special thermometer for this... a cooking thermometer will work just fine!  The gauge on the one shown at left starts at 130 degrees.

No brain surgery here... put the thermometer in a deep glass (keep the gauge dry) and fill it with hot water direct from the tap.  Be sure to run the water till it is fully hot.

How hot should your hot water be?

According to the US Department of Energy, a temperature of 120 degrees at the tap is adequate for most household chores with a minimal danger of scalding and maximal energy efficiency. However, that is the temperature at the tap, not in the tank. Tank temperature should be no less than 130 degrees to prevent bacterial growth, such as Legionnaires disease.

The only appliance that requires a hotter water is the dishwasher, with a recommended temperature of 140 degrees or higher for proper disinfection and cleaning. Since most dishwashers pre-heat the water to the proper temperature, lowering the setting of your water heater will have no effect. However, if you have turned the pre-heating function of your dishwasher off, you should turn it back on!

Lowering the temperature too much can have unintended consequences. You will need to use more heated water to obtain the same temperature at the faucet or shower. Thus, if your tank currently gives your family three showers in the morning, you might find the last person screaming!!

Adjusting tank-type electric water heaters...

The temperature of an tank-type electric water heater is controlled by a thermostat. The thermostat has a visible scale and is adjustable by turning the control to the desired temperature. The typical thermostat control is adjusted by using a screwdriver. Remember... the recommended minimum temperature is 130 degrees!

The thermostat is concealed behind a metal plate and may also be covered with insulation. TURN OFF THE POWER BEFORE REMOVING THE PLATE. This is important... there may be exposed high voltage wires under the cover.

IMPORTANT NOTE: Most electric water heaters have two thermostats... one near the top of the tank and one near the bottom. It is important that these both be adjusted to the same temperature. Otherwise, one element may never go on causing premature wear to the other. Also, the usable output of hot water or the time it takes to heat the tank may decrease... depending on which thermostat is set higher!

GOING ON VACATION? Turn off the power to your water heater to save even more energy!

Adjusting gas water heaters...

Unlike electric water heaters, gas water heaters have one heat source and one temperature control... near the bottom of the tank. Some gas water heaters have an exposed thermostat control which can be set to the desired temperature by rotating it. A few have the control concealed under a plate that can be moved aside to make the adjustment.

GOING ON VACATION? Lowering the temperature will save energy and money. Turning the water heater off will save even more.

However, if you don't want to or don't know how to relight the pilot light, don't turn the heater off!

Adjusting oil water heater temperature...

Oil water heaters have a simple temperature adjustment knob located on the side of the tank. If you haven't noticed this adjustment, add more lighting in the basement!

About furnace-fired oil water heaters...

Many homes have oil-fired furnaces which double as tankless water heaters. No separate tank is needed. There are some obvious advantages to this arrangement. First, you only have one appliance to be concerned with... the furnace. These integrated water heaters are very efficient and produce a continuous supply of hot water without the heat loss associated with tank-type heaters.

As nice as this "demand" system is, the picture isn't completely rosey. Furnace-fired water heaters do not produce a large volume of hot water per minute. Because of this inherent limitation, the outlet pipe is only 1/2" as opposed to the typical 3/4" outlet pipe from a tank-type water heater. If two hot water taps are opened at the same time, the temperature drop is sudden and unforgiving. For example, if you are in the shower and someone turns on the washing machine, you will be in for a chilly surprise!

This problem can be solved, but it requires the addition of a supplemental heating tank that provides additional storage capacity. Amtrol's Hot WaterMate (at left) has an internal heat exchanger that uses your furnace's hot water output to preheat water in the tank. By incorporating a separate thermostat, you have precise control over the water temperature.

A second drawback is that the hot water temperature is the same as the furnace temperature. The typical furnace temperature 140 to 160 degrees. At these temperatures the risk of severe scalding is high!

Though your first impulse might be to lower the temperature of the furnace, DON'T! Lowering the temperature of the furnace will radically change the built-in efficiency of your furnace and of your heating system as a whole.

Think about it… if you lower the temperature of the furnace, the temperature of the water circulating through your radiators will likewise be lowered. This will in turn increase the amount of time it will take for your home to be heated. All things being equal, it takes the same amount of oil to keep your home at a certain temperature regardless of how hot the water is. Therefore, your oil burner will have to cycle on and off more often to maintain this lower temperature because it will take longer for the temperature to rise. This will cause increased wear and tear on the furnace without any gain (or even a loss) in efficiency. The most inefficient moment in your furnace's operation is when it first starts up!

So instead of focusing on the furnace as the culprit, you can take measures to lower the faucet hot water temperature AFTER it leaves the furnace. This is done through the installation of a "mixing valve". A mixing valve is a simple thermostatically-controlled mechanism that mixes a little cold water with the hot water to lower the temperature. Mixing valves are adjustable to produce the desired water temperature, but it is wise to use a thermometer to verify the temperature at the tap. Installation does require some plumbing skills such as pipe cutting and soldering, but the end result is worth it!

Return to Water Heater Article Index