Water heater safety: scalding, relief valves and carbon monoxide

Updated November 10, 2026 · KeystoneProGuide editorial team

What are the dangers of a home water heater?

Three, mainly. Water hot enough to scald; a tank of heated water under pressure, which the code protects with a relief valve; and, for gas or oil heaters, carbon monoxide if the appliance malfunctions or its vent fails. Each has a specific rule or recommendation behind it, and a homeowner can check most of them without tools.

What temperature should the water heater be set to?

The Consumer Product Safety Commission's advice is 120 degrees Fahrenheit. Its childproofing guide says the setting can be 120 degrees or lower to prevent burns, and its long-standing advice to older consumers is to turn the heater down to 120 degrees to help prevent scalds. Young children and older adults are the two groups those pages are written for.

What protects against scalding at the shower?

A limit on the shower valve itself. The 2021 International Residential Code, which Pennsylvania's Uniform Construction Code adopts by reference, requires shower and tub-shower valves to have a way to limit their maximum setting to 120 degrees, adjusted on site so the water delivered does not exceed that. The CPSC also points to anti-scald devices for faucets and shower heads as a further safeguard. When a shower valve is replaced, ask the plumber to set that limit.

What does the relief valve do?

It keeps the tank from bursting. The code's introduction to its water heater chapter says heated water is commonly stored in pressurized tanks that must be protected against explosion by relief valves, and it requires either a separate pressure-relief and temperature-relief valve or one combination valve on every heater.

The code also sets rules for the valve's discharge pipe. Among them:

• no shutoff or check valve between the relief valve and the tank, or anywhere on the discharge pipe
• not connected directly to the drain system, and discharging through an air gap in the same room
• not smaller than the valve outlet, running downhill by gravity, and not trapped
• ending no more than 6 inches above the floor or receptor, where occupants can readily see it
• no threaded end, no valves and no tee fittings

Look at yours. A discharge pipe with a valve on it, one piped straight into a drain, or one that runs uphill does not meet those rules.

Does a water heater need a drain pan?

Where a leak would cause damage, yes. The code requires a tank-type heater in such a location to sit in a pan at least 1 1/2 inches deep, drained by a pipe of at least 3/4 inch to a suitable receptor or outdoors. When a heater is replaced, a pan drain is not required if none was installed before. ENERGY STAR's list of warning signs includes leaks from joints, seals or seams, and warns that ignoring them can end in a ruptured tank and water damage.

What about gas water heaters in a garage?

The code requires a water heater with an ignition source in a garage to be raised so the ignition source is at least 18 inches above the garage floor.

How does a water heater cause carbon monoxide?

Through malfunction or poor venting. The CPSC names malfunctioning water heaters among the fuel-burning appliances behind the more than 200 deaths a year in the United States from carbon monoxide produced by non-automotive consumer products. Its advice:

• Have appliances installed by qualified professionals and run according to the manufacturer's instructions and local building codes.
• During renovations, make sure appliance vents and chimneys are not blocked by tarps or debris.
• Install battery-operated CO alarms, or alarms with battery backup, on every level of the home and outside sleeping areas.
• Know the symptoms of mild poisoning: headache, fatigue, shortness of breath, nausea and dizziness, like flu without a fever.

If an appliance is found to be the source, the CPSC says not to use it until trained personnel have serviced it.

What can you check yourself once a year?

A handful of things, none needing tools.

• The temperature setting, against the CPSC's 120 degrees.
• The relief valve's discharge pipe, for any valve or tee fitting on it and for whether it ends near the floor where you can see it.
• The tank and its connections, for the corrosion, leaks and rust ENERGY STAR lists as warning signs.
• The area around a gas heater, for anything stacked against it or covering its vent; the CPSC warns that renovation tarps and debris can block appliance vents.
• The CO alarms, with a battery check; the CPSC's own safety materials include a reminder to check and change smoke and CO alarm batteries.

Who should work on these parts?

A licensed plumber, or the qualified professionals the CPSC refers to for fuel-burning appliances. In Philadelphia the city treats a water heater replacement as permitted plumbing work, listed on its Plumbing Permit fee table, so the finished work is inspected. Repair or replace covers the larger decision, what you can do yourself covers the safe homeowner checks, and plumbers are listed on the plumbers directory page.

Sources

1. Childproofing Your Home, U.S. Consumer Product Safety Commission
2. Home Safety Tips For Older Consumers, U.S. Consumer Product Safety Commission
3. Chapter 27 Plumbing Fixtures, 2021 International Residential Code, International Code Council
4. Chapter 28 Water Heaters, 2021 International Residential Code, International Code Council
5. 34 Pa. Code § 403.21. Uniform Construction Code., Commonwealth of Pennsylvania (Pennsylvania Code)
6. Carbon Monoxide Fact Sheet, U.S. Consumer Product Safety Commission
7. Carbon Monoxide Information Center, U.S. Consumer Product Safety Commission
8. When Should You Replace Your Water Heater?, ENERGY STAR
9. Get a Plumbing Permit, City of Philadelphia