Resources
35 Hot Water Heater Safety Features
How to Inspect the Safety of Domestic Hot Water Heaters – 34 inspection points
Potential Water Heater Safety Hazards and Other Water Heater Inspection Points That Should be Inspected or Checked
Hot Water Scalding Burn Hazards – temperature controls:
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 the temperature controls for each type of water heater, found in:
ANTI_SCALD VALVES & HOT WATER QUANTITY
ELECTRIC HOT WATER TEMPERATURE CONTROL
ELECTRIC SHOWER HEATER TEMPERATURE CONTROL
GAS HOT WATER TEMPERATURE CONTROL
INDIRECT WATER HEATER TEMPERATURE CONTROLS
OIL HOT WATER HEATER TEMPERATURE CONTROL
SCALDING TEMPERATURES & TIMES
TANKLESS HOT WATER HEATER TEMPERATURE CONTROL
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.
Proper relief valve location: In Carson Dunlop Associates’ sketch at left the pressure relief valve is improperly installed on the far side of the pressure reducing valve at the water heater.
Watch out: This is an example of a very dangerous installation. Thanks to Carson Dunlop Associates (found at page bottom, Click to Show or Hide), 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
Temperature-controlled, will turn off the fuel supply to the heater if its temperture becomes unsafe.
Details are at GAS WATER HEATER AUTOMATIC SHUTOFF
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
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
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.
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
- FIRE CLEARANCES INDOORS
- FIRE CLEARANCES for MASONRY CHIMNEYS
- FIRE CLEARANCES, METAL CHIMNEYS
- FIRE CLEARANCES, SINGLE-WALL METAL FLUES
Proper clearances to storage must be provided around fuel burning appliances.
See manufacturers instruction for exact clearance (typically a minimum of 18 inches). [refers to oil fired heating equipment]. – Information from Village of Mt. Prospect
Gas Water Heater Clearance Distances & Working Space – Calorifier or geyser clearances
- Water heaters require clearance space at least at the heater front for service.
- At back or sides clearance specifications vary by manufacturer and can be quite small. Here is an example of water heater clearance distances from an A.O. Smith water heater installation manual:
- Minimum clearances between the water heater and combustible and noncombustible construction are:
- 0 in. (0mm) from sides of the gas fired water heater
- 0 in. (0mm) from back of the gas fired water heater
- 4 in. (102mm) from front of jacket to closet door of the gas fired water heater
- 20 in. (508mm) from top of jacket of the gas fired water heater to combustible and noncombustible material.
- Minimum vent clearance:
- 1 in. (25mm)* for the gas fired water heater
- Provide 3 ft. (915mm) front of the gas fired water heater – clearance for servicing and adequate clearance between the jacket top & ceiling for servicing the flue area
Source: A.O. Smith, INSTRUCTION MANUAL, GAS WATER HEATERS MODEL GDV GDVT [PDF] A.O. Smith Water Heaters, 500 Tennessee Waltz Parkway, Ashland City, TN 37015 USA, Tel: 1-800-433-2545 Website: www.aosmithwaterheaters.com Email: parts@hotwater.com retrieved 2018/05/04, original source: www.hotwater.com/lit/im/res_gas/186589-000.pdf
Watch Out: The safe clearance distances for water heaters will vary by all of those features. So you’ll want to find the brand and model of your water heater, and then find its service manual and check the specific distances given for your particular heater.
Oil Fired Water Heater Clearance Distances & Working Space
- Provide ample clearance for the oil fired water heater on all sides for installation, adjustment, and replacement of burner, control components and other serviceable parts, such as the relief valve, power burner, thermostat, and/or drain valve.
- Minimum clearance from oil fired water heater to combustible construction is: Sides, 6”, Back, 6”, Front, 24”.
- If a chimney connector is used, the minimum clearance from the top of the oil fired water heater to the connector is 18”.
Source: HTP OIL FIRED WATER HEATER INSTALLATION MANUAL [PDF] retrieved 2018/05/04, HTP Products, 120 Braley Rd. P.O. Box 429 East Freetown, MA 02717-0429 USA, Website: www.htproducts.com, original source: http://www.htproducts.com/literature/lp-340.pdf
See WATER HEATER AGE & MANUALS
Tankless Water Heater Clearance Distances & Working Space
Using a Reliance Tankless Water Heater manual as an example, you need to maintain working space distances and fire clearances around the heater including at least:
- 12 – 36″ from the tankless water heater top, depending on model
- 12″ from the tankless water heater bottom
- 4″to 24″ from the tankless water heater front, depending on model
- 1″ from the tankless water heater back
- 3″ from the tankless water heater sides
Source: RELIANCE TANKLESS WATER HEATER MANUAL INDOOR Model TS-110-GI [PDF] Indoor Tankless watre heater, non-condensing 140K BTU Natural Gas
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
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
Is required in earthquake zones.
Water heaters must be secured against independent movement to reduce the chance of fire in the event of an earthquake
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.
[Click to enlarge any image]
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”
Appliances having an ignition source shall be elevated such that the source of ignition is not less than 18 inches (457 mm) above the floor in garages.
For the purpose of this section, rooms or spaces that are not part of the living space of a dwelling unit and that communicate with a private garage through openings shall be considered to be part of the garage.
See details at ELEVATE OIL or GAS BURNER 18″ ABOVE GARAGE FLOOR – IRC Requirement
Also,
Appliances shall not be installed in a location subject to vehicle damage except where protected by approved barriers.
See details at PROTECTION BOLLARDS for MECHANICAL EQUIPMENT
Original source of the text and illustration above:
- Stevens WA, COMMONLY USED RESIDENTIAL BUILDING CODES, IRC 2009, [PDF] retrieved 2019/05/08 original source: co.stevens.wa.us/landservices/documents/MECHANICALSECTION.pdf
- Other sections of this mechnaical code are given
Ffor 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).
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.
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
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.
Gas fired water heaters in some jurisdictions require an automatic gas shutoff valve that responds to high water heater temperature. See details
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 CLEARANCES, CODES & 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.
May be taxing the equipment beyond its intended use. See
WATER HEATERS for HOME HEATING USE?
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.
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.
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.
Leaks in the water heater tank body mean the heater needs to be replaced, and also that it may be unsafe.
Prohibited or restricted locations for LPG appliances: storage closets, bedrooms, bathrooms
IRC Mechanical Code 70. LPG APPLIANCES. Section M2005 IRC 2009
M2005.2 Prohibited locations.
Fuel-fired water heaters shall not be installed in a room used as a storage closet.
Water heaters located in a bedroom or bathroom shall be installed in a sealed enclosure so that combustion air will not be taken from the living space.
Direct-vent water heaters are not required to be installed within an enclosure.
M2005.2.1 Water heater access.
Access to water heaters that are located in an attic or under floor crawl space is permitted to be through a closet located in a sleeping room or bathroom where ventilation of those spaces is in accordance with this code.
Original source:
- Stevens WA, COMMONLY USED RESIDENTIAL BUILDING CODES, IRC 2009, [PDF] retrieved 2019/05/08 original source: http://www.co.stevens.wa.us/landservices/documents/MECHANICALSECTION.pdf
- Other sections of this mechnaical code are given at CHIMNEY HEIGHT & CLEARANCE CODE
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.
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
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
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 SUPPLY LINE SAFETY VALVES, OSVs.
PEX should not be connected directly to a water heater but should first be separated by at least 18″ of copper to reduce the risk of temperature damage to the PEX piping and subsequent leaks.
Where PEX is used for a water heater TPRV or “relief valve” discharge tube, check the relief valve and water heater manufacturer’s instructions to be sure that the relief valve discharge tube diameter reduction and thus flow construction caused by noraml PEX connectors is acceptable.
See details at PEX CONNECTIONS to WATER HEATERS
Gas fired water heaters should have a flue gas spillage switch that shuts off the gas valve if needed. See details
Used for producing domestic hot water can present a special scalding risk.
See ANTI SCALD VALVES
and
see TANKLESS COILS.
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.
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.
Water heaters require safe working space around the device regardless of the heater type.
Examples of water heater working space are found at
WATER HEATER or HOT WATER CYLINDER CLEARANCE DISTANCES & cleareance to combustibles
Specific clearances for working space at the water heater are given in the individual heater’s installation manual.