Water Heater Choices
Water Heater Choices
These maintenance tasks
may require working in tight
clearances and under task
lighting. Disconnect power
sources when working on
electrical appliances. Turn off
gas at cut-off valves before
working on gas lines. Be sure
to relight pilot lights.
Utility knife, garden hose for
draining tank
Insulation kit for water heater
– follow directions for gasfired or electric appliance
Pipe insulation and zip ties
or tape
Older water heaters will benefit
from additional insulation
since new tank water heaters
are better-insulated. Pipe
insulation, especially at and
around the heater can greatly
minimize heat loss. Flushing
the tank can extend the life
of the unit by minimizing
The Water Heating Appliance
A residential water heater provides domestic hot water
for a home and is commonly powered by either a fuelfired (natural gas, propane) or electric resistance
appliance. Other water heating appliances include:
„„ Solar thermal collectors which use free sunshine to
heat water
Hot water
„„ Electric heat pump water heaters that provide hot
water and help cool a home
„„ Heat recovery devices such as desuperheaters
which heat water with waste heat from a heat pump
There are a number of variables that affect the efficiency
and cost to provide hot water. Always look for the
Energy Guide label and consult the recipe card on Water
Heater Efficiency.
Tank vs. Tankless Water Heaters
Whether electric or fuel-powered, the water heating
appliance is usually either a traditional tank type or a
tankless unit.
Tank water heaters heat water to a set temperature and
store it. Typical sizes are 40-50 gallons for a standard
home, feature a cold water inlet and hot water outlet, a
temperature and pressure safety relief valve that should
be piped to a drain or outdoors, a sacrificial anode rod
(which is designed to corrode before the tank itself), a
thermostat to set the desired water temperature and an
insulated tank. Other installation features may include:
„„ Pipe insulation and heat traps - to reduce heat
losses during non-occupancy periods
Cold water
Be sure you have the
experience needed for these
maintenance tasks. If you are
in doubt, hire a contractor.
Types of Water Heaters and Maintenance Strategies
Gas line
Gas line
Drain valve
Cold water
Hot water
Burner cover
The tank or tankless decision (fuel-fired units shown)
should take into account initial cost, fuel demands and/
or flue considerations.
„„ Recovery takes time
„„ Takes up more space than the tankless variety
Tankless water heaters do not store hot water but rather
heat a small volume of water continuously. A tankless
unit can usually only meet the hot water demand of one
or two uses at a time, such as washing dishes or taking
a shower.
Electric resistance tankless water heaters are best suited
for small, remote and rarely used locations (e.g., guest
bathrooms) and are not recommended for whole house
water heating. Typically, small tank point-of-use electric
water heaters would be a better choice.
Advantages of a tankless water heater:
„„ Expansion tank - to reduce pressure spikes
(required by code in many areas)
„„ Takes up less space
„„ A drain pan - plumbed to a drain or outdoors in
case the tank leaks
„„ Provides a constant volume of hot water continuously
(but may lead to increased hot water consumption)
Advantages of a tank water heater:
„„ Usually cheaper to buy and install
„„ Utilizes a smaller heat input rate (usually either
electric resistance element or gas burner) than a
tankless unit
„„ Can provide a certain amount of hot water
regardless of how many fixtures are pulling from it.
Disadvantages of a tank water heater:
„„ Generally has greater standby losses due to the
surface area of the insulated tank
„„ Only heats water when it is needed
„„ Can reduce operating costs
Disadvantages of a tankless water heater:
„„ Usually higher purchase and installation cost
„„ May require a larger electric or fuel line than regular
water heater
„„ Combustion air and venting requirements for fuel
units may differ from tank models
„„ Potentially increased maintenance, especially in
areas with hard water
„„ Doesn’t overcome poor plumbing design
„„ Provides only a finite amount of hot water
Evaluate hazards and repair existing maintenance issues before proceeding with any do-it-yourself project; including knob and tube wiring, exposed electrical junctions and the like. Always follow
common-sense safety measures when working in tight work spaces.
cold water
DIY Maintenance and Upgrades
Heat traps
Flush the Tank.
hot water
hot water
cold water
Insulation blanket
Tank water heaters benefit from a periodic (6 months to one year) flushing
of the sediment from the bottom of the tank. First, turn off the heating
source. Connect a hose from the drain valve at the bottom of the tank to a
drain or outdoors, then to purge a few gallons of water. Also, depending on
the corrosiveness of the local water, a routine checking of the anode rod is
useful and replacement when substantially corroded can extend the tank life
many years (an excellent resource is www.waterheaterrescue.com).
Low Cost Add-ons. To provide greater efficiency, consider adding:
cut-outs for
heating coil
„„ An insulating blanket around the water heater which is easy and
inexpensive. Follow the directions with the insulating blanket, and:
• Do not cover the top on gas water heaters or block air to the burner
• Provide cutouts for access to controls
Cut-out for
combustion air
Heat Traps Should be Installed by a Plumber
Heat traps prevent warm water from rising upward and siphoning heat out
of a tank during periods of non-use. Fortunately, this effect can be minimized
since warm water will naturally rise up and travel, but will not flow down. As
a result heat traps can be formed by plumbing in a loop or inverted “U” at
the inlet/outlet water taps. Today many manufacturers include a check-valve
type of heat trap which helps achieve the same result.
& Exhaust
„„ Pipe insulation to as much of the hot water lines as possible.
Be sure to:
• Match the pipe insulation sleeve’s inside diameter to the water pipe’s
outside diameter for a snug fit
• On gas water heaters, pipe insulation should be kept at least
6 inches from the flue
• Tape or cinch pipe insulation with cable ties every 1-2 feet in length
Water Heater Safety
Combustion water heaters should have separate
combustion air that is isolated from the living area to
minimize the danger of backdrafting and potentially
introducing carbon monoxide and other combustion
byproducts into the living space. One option is to
locate the water heater outside of the living area (such
as in a garage). Another option is to place the water
heater inside a special combustion closet inside the
home that pulls in outside air for combustion through
high and low vents.
Direct vent gas water heaters bring in their own outside
air for combustion and then safely vent the combustion
exhaust gases through a concentric venting system.
Power vented gas water heaters use the air around
them for combustion but incorporate an electric
exhaust fan and a safety pressure switch to ensure
backdrafting will not occur.
Standard gas water heaters are typically exhausted with
flue pipe that must always be sloped with at least ¼”
of rise per 12” of horizontal run. Flue pipes that sag
or run too flat create a risk for poor drafting and can
have problems with condensation which can lead to
Direct vent gas water heater
Produced by Southface Energy Institute, www.southface.org
corrosion and flue pipe failure. Visually inspect for signs
of a corroded flue and contact a professional if detected.
If unsure, consult a professional for a combustion
appliance zone (CAZ) test.
Most standard gas water heaters incorporate a gas valve
with a standing pilot that is used to ignite the water
heater’s main burner when the tank thermostat calls
for heat. If the gas is shut off, the pilot will need to be
relit. Consult the manufacturer’s instructions for details.
Building codes require that combustion water heaters
in garages to be elevated above the ground in case of a
gasoline spill (gasoline vapors are heavier than air).
For electric and gas water heaters, set the tank
thermostat to approximately 120°F (medium setting).
This will reduce standby losses, minimize risk of scalding
and keep the tank temperature hot enough to prevent
bacterial growth. Also, ensure that the temperature
and pressure valve is piped down and preferably to the
outside in case the tank pressure gets too high and
scalding water is released.
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