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Warning about improper relief valve installation at a water heater (C) Carson Dunlop Associates 33 Hot Water Heater Safety Features
Hot Water Cylinder / Water Heater Safety Inspection

  • WATER HEATER SAFETY - CONTENTS: Checklist of water heater safety inspection points. Authorities recommending water heater safety inspections. How to compare various safety features of hot water heating methods: electric, gas, high efficiency gas, oil, high efficiency oil, solar, tankless coils.
  • POST a QUESTION or READ FAQs about water heater safety & safety devices
  • REFERENCES
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Water heater safety - hot water cylinder safety:

This article discusses the need and procedure for regular safety inspections of water heating equipment. We list authoritative citations supporting the need for water heater safety checks.

Included are 31 water heater safety checklist items.



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How to Inspect the Safety of Domestic Hot Water Heaters - 33 inspection points

Gas fired water heater fire (C) Daniel Friedman

Authorities recommend a periodic safety inspection of all water heating equipment, including all types of water heaters.

[Click to enlarge any image]

Our photo shows the results of a fire at an LP gas fired water heater installed outdoors in Gogorron, San Luis Potosi, Mexico.

Potential Water Heater Safety Hazards and Other Water Heater Inspection Points That Should be Inspected or Checked

Except for our having placed two very common water heater safety concerns - scalding and relief valve problems - at the top of this list, the rest of our water heater safety inspection list is arranged alphabetically and includes links to more details about each item.

  1. Hot Water Scalding Burn Hazards: water heater temperatures may be set too high, risking serious or even fatal scalding hot water burns to building occupants. Details are
    at ANTI SCALD VALVES.

    Watch out for hot water scalding hazards and unsafe water tank or calorifier pressures: By the way, typical safe temperatures in water heaters or calorifiers used for washing and bathing are around 104 degF up to a max (and risk of scalding) of 120 degF, or from at about 40-49 °C.

    Temperature settings: on the water heater, setting the temperature very high in an attempt to obtain more hot water can be dangerous and lead to serious scalding burns for the building's occupants unless water tempering or mixing valves or other temperature safety controls are provided and properly set at the plumbing fixtures.

    At a temperature setting of 100 degF or below most water heaters are unlikely to scald an occupant; more than 5 minutes exposure at 120 degF are required to produce 2nd & 3rd degree burns on adult skin.

    Hot Water Scalding Burn Warning: MIXING / ANTI-SCALD VALVES contains a table of hot water temperatures which are safe and which explains the risk of second and third degree scalding burns that occur at different water temperatures and exposure times.
    Also
    see ANTI_SCALD VALVES & HOT WATER QUANTITY.

    Also see SCALDING TEMPERATURES & TIMES

  2. Unsafe Water Heater Pressure/Temperature Relief Valves: Water heaters [and any pressurized tank] require a pressure [and on heaters, temperature] safety relief valve or TP valve as well as an extension or discharge tube. Missing, modified, improper version, improper discharge tube piping.

    See details at RELIEF VALVE, WATER HEATER where we also discuss procedures for testing water heater pressure/temperature relief vales.
    Warning about improper relief valve installation at a water heater (C) Carson Dunlop Associates
    Proper relief valve location: In Carson Dunlop's sketch at left the pressure relief valve is improperly installed on the far side of the pressure reducing valve at the water heater. This is a very dangerous installation. Thanks to Carson Dunlop Associates, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article.

    In some locations where hard water is found or where water supply piping materials cannot withstand higher pressures, a thermal expansion control valve is also used to drain excess hot water tank pressure. These separate water system expansion control valves, discussed below.

    Proper TPR discharge or drain piping: improperly installed, routed, sized, connected drain piping at a water heater risks scalding a bystander or a catastrophic BLEVE explosion.
    See RELIEF VALVE DISCHARGE TUBE

    BLEVE explosions
    or boiling liquid vapor explosions can occur at both domestic water heaters (calorifiers or geysers) and at hot water heating boilers (hydronic heating systems).

    Information from the Colleyville Building Dept.

    Improperly installed safety devices: If the temperature and pressure relief valve (T&P-valve) and similar safety devices (e.g. expansion tank) are not properly installed the result can be deadly. The T&P-valve is designed to prevent a water heater tank from exploding if temperatures and/or pressures exceed their safe operating limits. There are many documented cases where water heaters have malfunctioned with catastrophic results leading not only to property damage but to loss of life as well. Exploding water heaters have been described as bombs exploding.

    More about temperature/pressure relief valves or TPRs is at RELIEF VALVES - TP VALVES
  3. Automatic gas shutoff valves for gas fired water heaters, temperature-controlled, will turn off the fuel supply to the heater if its temperture becomes unsafe. Details are at AUTOMATIC GAS WATER HEATER SHUTOFF
  4. Gas line fire safety valves will shut off the fuel supply to a gas-fired water heater in the event of a nearby fire.

    Details are at GAS LINE FIRE SAFETY VALVES
  5. Water heater or cylinder chimneys, vents, and flues to avoid fire or flue gas spillage: for gas or oil fired water heaters the flue vent connector, draft hood or barometric damper, and chimney must be safe to avoid fire and potentially dangerous carbon monoxide hazards.

    See CHIMNEY INSPECTION DIAGNOSIS REPAIR. Also note this information from the Colleyville Building Dept.

    Improperly installed venting system: If improperly installed, the water heater venting system may fail to function properly. The result of that failure can be deadly. If the venting system is installed incorrectly it could disconnect and leak carbon monoxide into your home.

    Carbon monoxide (CO) is a colorless, odorless, extremely poisonous gas formed by incomplete combustion of carbon or carbonaceous material; also referred to as the silent killer.


    Also see PLASTIC PLEXVENT ULTRAVENT RECALL.
  6. Water heater or cylinder combustion gas venting for water heaters: any fossil fuel fired water heater (oil or gas fired) requires safe venting of the combustion products, through a chimney or in the case of high efficiency heaters, through a plastic vent line. Watch out: venting a small gas fired water heater through a large old masonry chimney may be unsafe.
    See CHIMNEYS for details.
    The presence of soot around gas fired flues or vents is an indication of a dangerous condition.
    See CARBON MONOXIDE - CO.

    Also see SOOT on OIL FIRED HEATING EQUIPMENT.
    Information from the Colleyville Building Dept. is below:

    Water heater installed in a closet or confined space: If your water heater is installed in a closet or confined space it is required to have the appropriately sized upper and lower combustion air openings. If a gas appliance such as a water heater is not provided with the appropriate amount of combustion air it will malfunction.

    Typically what will happen is the gas burner will be starved for oxygen and the burner flame will go from a short blue flame to a large yellow flame causing the flame to escape the combustion chamber possibly (most likely) causing a fire.
  7. Water heater or cylinder clearance to combustibles: fire safe clearance between flue vent connectors or chimneys and combustibles is required, typically 1" for "zero clearance" metal flues, up to 18" for flue vent connectors serving oil fired heating equipment. See

  8. Water heater or cylinder combustion air: any fossil fuel fired water heater (oil or gas fired) requires combustion air. The volume of air intake to the utility room where the heater is installed depends on the BTUs of the device and the type of fuel. Watch out: installing a gas or oil fired heater in a small confined space whose door is shut and which lacks adequate combustion air is unsafe.

    See details
    at COMBUSTION AIR DEFECTS,
    and
    at COMBUSTION AIR for TIGHT BUILDINGS.

    More information is
    at COMBUSTION GASES & PARTICLE HAZARDS
    and
    at COMBUSTION PRODUCTS & IAQ.
  9. Damage protection for water heaters: Also referred to in some communities as "bollard or barrier" to protect the water heater, water heaters in garages should be protected from mechanical damage such as being struck by an auto
  10. Earthquake Strapping for water heaters: required in earthquake zones, water heaters must be secured against independent movement to reduce the chance of fire in the event of an earthquake
  11. Electric wiring and overcurrent protection for electric water heaters: proper wiring size, connections, overcurrent protection and grounding are important for electrical safety. Also a visual inspection of the electric water heater's thermostats can often detect signs of failure or overheating at those components.
    Information from the Colleyville Building Dept.

    Improperly installed electrical wiring: If your water heater is powered by electricity the electrical circuit may not be correctly sized to accommodate the minimum required amperage draw to the water heater replacement. This can lead to electrical inefficiencies and may cause a fire or damage electrical equipment.

  12. Elevating stand for water heater: required by some building codes that specify that the water heater must be elevated above floor level, for example for water heaters installed in a garage. Note that many new water heaters are FVIR rated or "flammable vapor ignition resistant"
  13. Electric Water heater bottom insulating board: for electric water heaters in unheated spaces, the tank is placed on a non-compressible insulated surface with at least an R-10 insulation rating to reduce heat loss out of the bottom of the water heater tank (saving on operating cost).
  14. An Expansion Control Valve is used on water heaters in south and Western Australia where hard water is found, and in some other countries or other jurisdictions.

    The Expansion Control Valve discharges water into a drain to relieve excess pressure in the hot water tank. The purpose of this valve is to release pressure through a separate control so that the safety provided by the Temperature and Pressure Relief valve is not compromised by clogging from minerals should that valve frequently open.

    The expansion control valve should be tested every six months, following the same procedure as for temperature and pressure relief valves as we described above.

  15. Thermal Expansion Tanks & Thermal Expansion Control Valves for water heater systems: Expansion tanks are required in some areas when the customer is on a “closed” water system: when water is heated in a closed water system, thermal expansion can cause rapid increases and decreases in system pressure which can in turn cause spillage at pressure/temperature relief valves (and related building water, flood, or mold damage), or damage to other plumbing components.

    Amtrol Inc. provides the THERM-X-TROL® line of thermal expansion shock absorbers - expansion tanks for domestic hot water systems. Quoting from the company's product literature:

    Thermal expansion occurs as domestic water is heated. Left unchecked, the resulting pressure increase can cause relief valve discharge and other potentially unsafe conditions. Therm-X-Trol® expansion tanks absorb this expanded water, keeping water pressure at a safe level.

    Water heater manufacturers and plumbing codes require the installation of an expansion control device if a backflow preventor, pressure reducing valve or check valve is installed in the domestic supply line. Therm-X-Trol satisfies all manufacturers' requirements. - Amtrol (2014)

    An expansion tank or additional pressure/temperature relief valves can prevent these problems and may also extend the life of the water heater. Details are
    at HOT WATER EXPANSION TANKS
    and
    at HOT WATER EXPANSION VALVES
  16. Flame shield on gas or oil fired water heaters or cylinders: Gas or oil fired water heaters include a flame shield around the port used to inspect the burner - it must remain in place and be undamaged. Look for signs of flame spillage or roll-out at gas fired water heaters.
  17. Gas shutoff valves for water heaters: Gas fired water heaters in some jurisdictions require an automatic gas shutoff valve that responds to high water heater temperature. See details
    at GAS SHUTOFF VALVES.
  18. Gas piping and gas piping drip leg on gas fired water cylinders / heaters: Gas piping must be correctly installed, using the proper piping materials, connections, shutoff valves, and must not be leaking.

    The drip leg also referred to as a "dirt leg", the drip leg is required by some water manufacturers to collect moisture (rare in modern fuel gases) or dirt to keep these harmful materials out of the water heater gas burner. See
    details at GAS PIPING DEFECTS.

    Also see GAS LEAK DETECTION, LP / NG.

    From the Colleyville Building Dept.

    Improperly installed gas piping: If the gas-supply piping connected to your water heater is incorrectly sized the gas system’s ability to properly supply the necessary gas demand to your water heater may be compromised. This could potentially create energy inefficiencies and lead to a gas burner malfunction or incomplete combustion of the fuel gas which could ultimately cause a fire or a carbon monoxide leak.
  19. Home heating using a water heater: may be taxing the equipment beyond its intended use. See
    WATER HEATERS for HOME HEATING USE?
  20. Indirect fired water heaters: use heat from an independent source such as a separate gas or oil fired heating boiler or solar heating system to heat water in the hot water tank. But these tanks also require temperature/pressure relief valve, safe plumbing, and scald protection.

    See INDIRECT FIRED WATER HEATERS
  21. Insulation on water cylinders / water heaters: as an add-on extra water heater tank insulation is not generally recommended by water heater manufacturers.

    If insulation is improperly installed on a water heater it may make the system very unsafe, including blocking the draft hood on a gas fired water heater (a carbon monoxide hazard) or blocking a relief valve preventing safe pressure/temperature relief valve operation.

    See INSULATE HOT WATER TANK?.
  22. Leak pan and drain beneath water heaters: for water heaters installed on a wood floor without a drain, in an attic or ceiling where water damage from a leaking tank can damage the building, possibly causing a costly mold contamination, insect attack, or structural rot.
  23. Leaks in water heaters: leaks in the water heater tank body mean the heater needs to be replaced, and also that it may be unsafe.
  24. Mobile home water heater safety:

    see MOBILE HOME WATER HEATER DEFECTS
  25. Noises: noises in the water heater may indicate that an excessive lime or scale buildup has occurred, possibly increasing water heating costs, reducing the quantity of hot water available, and in some circumstances, it may affect the safety and life of the water heater tank.

    Details are at NOISES COMING FROM WATER HEATER.
  26. Odors: such as a "rotten egg" smell or sewer gas smells may be due to a bacterial contamination in the heater tank or due to a deteriorated sacrificial anode

    See (ANODES & DIP TUBES on WATER HEATERS

    or it may be due to contaminants in the water supply. See ODORS IN WATER
    and

    see SEWER GAS ODORS
  27. Oil burner noises, smoke, odors and on occasion soot on and around an oil fired water heater indicate improper operation of the equipment and risk a puffback or other potential safety hazards.
    See OIL BURNER NOISE SMOKE ODORS.
  28. Oil shutoff valves: oil fired water heaters should always have their own oil safety valve: a special valve installed on the oil line near the water heater and which will automatically close and stop the flow of oil to the water heater should a fire occur.

    Watch out: often in a building where there is an oil fired heating system as well as an oil fired water heater, the installer may have installed the safety valve only at the oil tank or only at the heating boiler or furnace.

    See details at OIL LINE SAFETY VALVES, OSVs.
  29. Spill switch on gas flues for water heating appliances: Gas fired water heaters should have a flue gas spillage switch that shuts off the gas valve if needed. See details
    at SPILL SWITCH, FLUE GAS DETECTOR.
  30. Tankless coils used for producing domestic hot water can present a special scalding risk.
    See ANTI SCALD VALVES
    and
    see TANKLESS COILS.
  31. A Water Heater Temperature Limiting Valve that limits the outgoing water temperature to 50 degC in order to prevent scalding is installed on water heaters in some locations. This valve should be checked annually by measuring water temperature at a nearby water taps, making sure that the water delivered closest to the water heater is not hotter than 50 degC.
    See ANTI SCALD VALVES.
  32. Water pressure reducing valves / water pressure regulators for water heaters: if the building water pressure gauge reading is ever found at 80 psi or higher, you will want to install a water pressure regulator at the point where water supply enters the building. If your building already has a water pressure gauge installed, it may be defective or it may be set too high.
    WATER PRESSURE REGULATOR ADJUSTMENT discusses how to adjust a water pressure regulator to the proper setting.   
  33. Working space around the water heater: Water heaters require safe working space around the device regardless of the heater type

Building Authorities & Other Sources Recommending Water Heater Safety Inspections

Thanks to reader D.B. for discussing the need for water heater safety inspections, suggesting some of the water heater inspection requirement code sources above, and for suggesting the need for documenting sources of authority, building codes, water heater manufacturers, water heater operating and installation manuals, and other sources recommending inspection and safety practices involving water heaters (as well as other tanks and pressurized containers in buildings).

A Comparison of the Relative Safety of Different Types of Water heaters

Gas water heater with draft hood removed (C) Daniel Friedman

In the LP gas fired water heater shown in our photo, the installer had trouble fitting the draft hood atop the heater since there was then not enough overhead clearance to route the flue out of the building. The installer has thoughtfully left the draft hood he removed, an important safety device, sitting atop the water heater as a reminder that this is an improper installation.

There is just too much subjectivity to make a sensible answer to this question. Some people are frightened by the prospect of a natural or LP gas explosion in a building.

But while it's difficult to set heating oil on fire and so explosions based on the fuel character may be less likely than with an LP or natural gas system, an oil-fired water heater runs at much higher burner and exhaust flue temperatures and so can prevent other types of fire risk.

Most critical with any water heater are that the heater is properly installed and includes the required safety controls such as those responsible for limiting temperature and pressure.

Any water heater should include a temperature and pressure relief valve installed of the proper type and at the correct location. Gas-fired devices also should include flue-gas spillage detectors. Oil-fired devices should also include a fire-safety valve that shuts off fuel to the appliance in case of fire.

We guess that proper installation, inspection, and maintenance make more difference in the safety of a water heater than the innate differences among heater types, fuels, etc.

List of Hot Water Heater Safety Devices and Features

  1. Pressure/Temperature Relief Valves: Water heaters (and any pressurized tank) require a pressure and temperature safety relief valve or TP valve as well as an extension or discharge tube. In Carson Dunlop's sketch at page top the pressure relief valve is improperly installed on the far side of the pressure reducing valve at the water heater. This is a very dangerous installation.

    See RELIEF VALVE, WATER HEATER
  2. Hot water expansion tanks: handle the pressure increase from normal water heating and prevent dangerous dripping at the TPR valve on the heater

    See HOT WATER EXPANSION TANKS
  3. Spill switch on gas flues: Gas fired water heaters should have a flue gas spillage switch that shuts off the gas valve if needed
  4. Gas shutoff valves: Gas fired water heaters in some jurisdictions require an automatic gas shutoff valve that responds to high water heater temperature.

    See AUTOMATIC GAS WATER HEATER SHUTOFF
    and
    GAS LINE FIRE SAFETY VALVES
  5. Oil shutoff valves: oil fired water heaters should always have their own oil safety valve: a special valve installed on the oil line near the water heater and which will automatically close and stop the flow of oil to the water heater should a fire occur. Watch out: often in a building where there is an oil fired heating system as well as an oil fired water heater, the installer may have installed the safety valve only at the oil tank or only at the heating boiler or furnace.

    See OIL LINE SAFETY VALVES, OSV
  6. Flame shields: Gas or oil fired water heaters include a flame shield around the port used to inspect the burner - it must remain in place.
  7. Combustion air: any fossil fuel fired water heater (oil or gas fired) requires combustion air. The volume of air intake to the utility room where the heater is installed depends on the BTUs of the device and the type of fuel. Watch out: installing a gas or oil fired heater in a small confined space whose door is shut and which lacks adequate combustion air is unsafe.
  8. Combustion gas venting by a chimney: any fossil fuel fired water heater (oil or gas fired) requires safe venting of the combustion products, through a chimney or in the case of high efficiency heaters, through a plastic vent line. Watch out: venting a small gas fired water heater through a large old masonry chimney may be unsafe.

    See CHIMNEYS for details.
  9. Temperature settings: on the water heater, setting the temperature very high in an attempt to obtain more hot water can be dangerous and lead to serious scalding burns for the building's occupants unless water tempering or mixing valves or other temperature safety controls are provided and properly set at the plumbing fixtures.

    At a temperature setting of 100 degF or below most water heaters are unlikely to scald an occupant; more than 5 minutes exposure at 120 degF are required to produce 2nd & 3rd degree burns on adult skin.

    Hot Water Scalding Burn Warning: MIXING / ANTI-SCALD VALVES contains a table of hot water temperatures which are safe and which explains the risk of second and third degree scalding burns that occur at different water temperatures and exposure times.
  10. Working space: Water heaters require safe working space around the device regardless of the heater type
  11. Damage protection: Water heaters in garages should be protected from mechanical damage such as being struck by an auto
  12. Water Heater Expansion Tanks: Expansion tanks are required in some areas when the customer is on what is called a “closed” water system. See our discussion of how and why, above.
  13. Regular safety inspections: Water heaters should be periodically inspected for safety and evidence of damage or leaks. An example of an unsafe water heater is one whose relief valve has been leaking, modified, or blocked, or a heater whose exhaust flue lacks proper fire clearance distances.

We list and compare different types of water heating systems at WATER HEATER COMPARISONS, PROPERTIES.

...


Continue reading at WATER HEATER TEMPERATURE CONTROLS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see HOT WATER ANTI-SCALD REGULATIONS

Or see Legionella BACTERIA in WATER HEATERS

Or see RELIEF VALVE, WATER HEATER

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WATER HEATER SAFETY at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to ARTICLE INDEX to WATER HEATERS

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