Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
This page is about measuring the hot water your taps actually deliver, with a thermometer, and writing the number down. It needs no tools you cannot buy in a supermarket and it takes about twenty minutes. The reason to bother is speed: CPSC publishes that most adults suffer third-degree burns after two seconds in 150 degree water, that burns also occur after six seconds at 140, and after thirty seconds at 130. A small child or an older adult is burned faster than that, and a scald is the one household injury that happens before you can react to it. What this page does not do is change anything on the water heater. No thermostat, no control, no valve.
It also will not tell you what to set your water heater to, because the authorities genuinely disagree and this site does not split the difference. CPSC urges people to lower their water heaters to 120 degrees Fahrenheit to reduce scald injuries. CDC says to store hot water above 140 degrees Fahrenheit, and OSHA says the same, because that is the floor for controlling Legionella bacteria in the pipework. Both positions come from federal authorities, both are about a real way people get hurt, and averaging 120 and 140 would produce a number that nobody stands behind. The manual for your own water heater is the document that governs your unit. What this page gives you is the measurement, so that when you read that manual you are holding a real number instead of a guess.
Safety
DO NOT TOUCH THE WATER DURING THIS MEASUREMENT.
Hot water from a tap can burn your skin in seconds.
Necessary equipment
| Item | Note |
|---|---|
| Candy thermometer or meat thermometer | CPSC names these two types for this measurement. |
| Cup that holds hot liquids safely | A glass measuring cup or a ceramic mug is satisfactory. |
| Pen and paper | Use these to record the reading and the time. |
| Manual for your water heater | The manual gives the temperature limits for your unit. |
Before you start
Estimated 5 min to 7 min
- Find a candy thermometer or a meat thermometer.3mReport a problem with step 1, Before you start
- CPSC names these two types for this measurement.
- Do not use a thermometer for the human body.
- Do not use an infrared thermometer, because it reads the surface of the cup.
- Find a cup that holds hot liquids safely.1mReport a problem with step 2, Before you start
- A glass measuring cup or a ceramic mug is satisfactory.
- Do not use a thin plastic cup.
- Do not use hot water for two hours before this measurement.<1mReport a problem with step 3, Before you start
- CPSC gives this condition for the most accurate reading.
- The first measurement of the morning also agrees with this condition.
- Select the tap that the persons at most risk use.<1mReport a problem with step 4, Before you start
- A bath tap and a shower are the two that cause the most scalds.
- Measure at a kitchen tap only if no other tap is available.
Measure the temperature at the tap
Estimated 4 min to 8 min
- Put the cup in the sink.<1mReport a problem with step 1, Measure the temperature at the tap
- The cup stays in the sink for all of the measurement.
- Water that splashes from the cup stays in the sink.
MAKE SURE THAT NO CHILD IS NEAR THE SINK BEFORE YOU OPEN THE TAP.
Hot water burns the skin of a child more quickly than the skin of an adult.
- Open the hot tap fully.<1mReport a problem with step 2, Measure the temperature at the tap
- Do not open the cold tap.
- A mixer tap must be at its hottest position.
- Continue the flow until the temperature of the water is constant.2mReport a problem with step 3, Measure the temperature at the tap
- The temperature increases while the hot water flows through the pipe.
- This can need more than one minute at a tap far from the water heater.
- Steam above the sink is a sign that the water is very hot.
DO NOT PUT YOUR HAND IN THE WATER FLOW.
Water at 140 °F (60 °C) burns the skin of an adult in about six seconds.
- Fill the cup with the hot water.<1mReport a problem with step 4, Measure the temperature at the tap
- Keep your hands clear of the flow.
- Fill the cup to a depth that covers the probe of the thermometer.
- Close the tap.<1mReport a problem with step 5, Measure the temperature at the tap
HOLD THE THERMOMETER BY ITS HANDLE ONLY.
The metal probe is hot after you remove it from the water and can burn you.
- Put the thermometer in the cup.<1mReport a problem with step 6, Measure the temperature at the tap
- The probe must not touch the bottom of the cup.
- The bottom of the cup is cooler than the water.
- Read the temperature when the indication is constant.<1mReport a problem with step 7, Measure the temperature at the tap
- A thermometer with a dial can need 30 seconds to become stable.
- Read the scale at the level of your eye.
- Write the reading, the tap and the time in your records.1mReport a problem with step 8, Measure the temperature at the tap
- The time is necessary, because the temperature changes through the day.
Compare the reading
Estimated 8 min to 18 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Source: Avoiding Tap Water Scalds (CPSC Publication 5098) · tier 1 · accessed 2026-07-29
Source: Controlling Legionella in Potable Water Systems · tier 1 · accessed 2026-07-29
Source: Legionellosis (Legionnaires' Disease and Pontiac Fever) - Control and Prevention · tier 1 · accessed 2026-07-29
Source: Avoiding Tap Water Scalds (CPSC Publication 5098) · tier 1 · accessed 2026-07-29
Source: Avoiding Tap Water Scalds (CPSC Publication 5098) · tier 1 · accessed 2026-07-29
Source: Avoiding Tap Water Scalds (CPSC Publication 5098) · tier 1 · accessed 2026-07-29
Source: Electric Residential Hybrid Water Heater Use & Care Manual (AP23657 Rev 04) · tier 1 · accessed 2026-07-29
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Compare your reading with the specifications on this page.2mReport a problem with step 1, Compare the reading
- The specifications name each authority and give its number.
- The authorities do not agree, and this page does not reconcile them.
- Read the temperature instructions in the manual for your water heater.5mReport a problem with step 2, Compare the reading
- The manual of the manufacturer is the only correct source for your unit.
- The model number and the serial number are on the rating plate.
- Many manufacturers supply the manual from their website at no cost.
IF THE READING IS MORE THAN 130 °F (54 °C), TELL EACH PERSON IN THE HOME.
Water at this temperature burns the skin of an adult in about thirty seconds.
- If the reading is more than the limit in your manual, speak to a plumber.2mReport a problem with step 3, Compare the reading
- Do not adjust the temperature control on the water heater yourself.
- Give the plumber your written reading and the time of the measurement.
After the measurement
Estimated 6 min to 11 min
- Do a test of the water with your hand before each bath.<1mReport a problem with step 1, After the measurement
- CPSC says to do this test each time, and for a shower also.
- A measurement from last month does not tell you the temperature today.
- Do the same measurement at each tap that a child uses.5mReport a problem with step 2, After the measurement
- The temperature is different at each tap.
- A tap near the water heater is usually the hottest.
- Do the measurement again after any work on the water heater.<1mReport a problem with step 3, After the measurement
- A new water heater does not always arrive at the same setting.
- A repair can change the setting.
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- water heater
- Also called: hot water heater, hot water tank, hot water cylinder, boiler, geyser, immersion heater, water boiler
- scald
- Also called: hot water burn, tap water burn, burned by hot water, water too hot
- temperature setting
- Also called: water heater temp, thermostat setting, water heater 120 or 140, how hot should my water be, hot water heater too hot
- mixing valve
- Also called: anti-scald valve, tempering valve, thermostatic mixing valve, TMV, temperature limiting valve
When to use a professional
Do not adjust the temperature control on the water heater. This page gives you a measurement and stops there. A qualified plumber must make any change to the setting. A qualified plumber must do all work on a control or a valve.
Speak to a qualified plumber if your reading is above the limit in the manual for your unit. Speak to a qualified plumber also if the reading changes by a large amount. A large change between two measurements at the same tap can be a sign of a fault.
Speak to a qualified plumber about a mixing valve. Do this if a small child or an older adult lives in your home. Rheem states in its manual that a mixing valve reduces the temperature at the point of use. Only a qualified person can select and install a mixing valve.
If your water heater burns a gas supply, CPSC says to call your gas utility. Ask the utility for instructions about the temperature. Do not open the cabinet of the water heater. Do not remove any panel.
Common questions
What temperature should my hot water heater be set to, 120 or 140?
This page will not pick one for you, because the two answers come from different federal authorities and both are about a real way people get hurt. CPSC urges lowering water heaters to 120 degrees Fahrenheit because tap water scalds send people to hospital, and it publishes how fast that happens. CDC and OSHA both say to store hot water above 140 degrees Fahrenheit because Legionella bacteria multiply in the range below that. Averaging them would produce 130, a number that neither authority recommends and that sits inside the growth range CDC names while still burning an adult in about thirty seconds. The document that actually governs your unit is its own manual, which is why the whole point of this page is to get you a real measured number to take to it.
How hot is too hot for a shower or a bath?
The published burn times are the useful way to think about it rather than a single cutoff. CPSC gives thirty seconds to a burn at 130 degrees, six seconds at 140, and two seconds at 150. Those are figures for adults, and children and older adults burn faster because their skin is thinner. A manufacturer's own table, printed in a Rheem use and care manual and credited to the Shriners Burn Institute, gives even shorter times at the top of that range. Whatever your measurement says, CPSC's standing advice is to hand-test the water before every bath and never to leave a child unattended in a bathroom.
Why does my water come out lukewarm at one tap and scalding at another?
Distance and pipework. Water sitting in a long uninsulated run cools down, so a tap far from the water heater delivers cooler water and takes longer to come up to temperature, while a tap close to it can deliver near-storage temperature almost immediately. Some homes also have a mixing valve or a tempering valve fitted at the heater or at a single fixture, which limits that outlet and not the others. This is exactly why the procedure asks you to measure at the tap the most vulnerable person actually uses, and then repeat it elsewhere, rather than measuring once and assuming the house is uniform.
Can I just use a normal kitchen thermometer?
A candy thermometer or a meat thermometer is what CPSC names, and either is fine. What will not work is a medical thermometer for taking a person's temperature, because it does not read high enough, and an infrared thermometer is unreliable here because it reads whatever surface you point it at rather than the water. If your thermometer has a dial, give it half a minute to settle before you read it. There is no need to buy anything specialised.
Is it dangerous to turn the water heater down myself?
This page does not cover adjusting it, and that is deliberate rather than squeamish. On an electric unit the adjustment is behind access panels with live terminals, and CPSC's own guidance is to shut off the supply first or to have the utility do it. On a gas unit CPSC says to call the gas utility for instructions because the controls differ between models. Either way you are working on the appliance rather than measuring it, which puts it past the boundary this site draws. Get the measurement, then hand it to a plumber.
If I turn it down to 120, am I going to get Legionnaires' disease?
That is the honest question underneath the disagreement and nobody should pretend it away. CDC and OSHA name 140 degrees as a storage minimum precisely because Legionella grows in the warm range below it, and CDC gives that growth range as roughly 77 to 113 degrees Fahrenheit. CPSC weighs a different harm, tap water scalds, which are common, immediate and heavily concentrated among young children and the elderly. Which risk matters more in your household depends on who lives there and on what your plumbing looks like, and that judgement belongs to your manufacturer's manual, your plumber and your doctor rather than to a checklist. What this page can do is make sure you know what your water is actually doing.
Related procedures
- How to find and record the model and serial number of every appliance in the house
- How to flush a water heater
- How do I check if my water heater's pressure relief valve pipe is installed correctly
- Where is the water under my hot water heater coming from, and does it mean I need a new one?
- How do I read the label on my hot water heater and figure out what the numbers mean
- How old is my water heater and how do I read the serial number
- How do I insulate the hot water pipes at my water heater
- How to descale or flush a tankless water heater, and whether vinegar or a CLR-type descaler is safe to use
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1Avoiding Tap Water Scalds (CPSC Publication 5098)
- Tier 1Controlling Legionella in Potable Water Systems
- Tier 1Legionellosis (Legionnaires' Disease and Pontiac Fever) - Control and Prevention
- Tier 1Electric Residential Hybrid Water Heater Use & Care Manual (AP23657 Rev 04)
- Tier 1Water Heating 101
Revision history
Current version 1 · updated 2026-07-29 · next review due 2027-07-29
- v1 · 2026-07-29First draft. Measurement method and the scald time figures from CPSC Publication 5098. The storage temperature publishes as a recorded disagreement between CPSC on one side and CDC and OSHA on the other, and is not reconciled. Burn times published as a second recorded disagreement between CPSC and a Rheem use and care manual. No step touches a control, a thermostat or a valve.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.