Water heater
expansion tank
Hot water heater expansion tanks
The addition of a hot water heater expansion tank
can both resolve and prevent high water pressure. If either
undetected or unresolved, excessive pressure can seriously compromise
the durability, performance and the efficiency of the system.
Inspecting
for high pressure is an important water heater
maintenance
procedure that should be performed periodically. A storage tank
with pressure that exceeds 80 psi (pressure per
square inch) when the heating element is on and hot water is not in use
will require an expansion tank in most cases.
With that said, storage tanks that don't
experience high water pressure stand to benefit as well. Before
installing an expansion tank consider the
following;
Warning
- High Water Pressure and Gas Powered Storage Tanks
Overtime excessive
pressure can become a serious safety concern in gas
water heating tanks. High water pressure can ultimately compromise, or
even collapse,
the
internal flue that's immersed within the storage tank.
Internal flue damage can result in the build up of
carbon monoxide, which is very dangerous. If your water heating storage
tank has high
water pressure and you suspect that the internal flue may have been
damaged or compromised, consult with a local water heating
professional immediately.
Thermal
expansion
Thermal expansion occurs in all systems. When the
heating element significantly raises the temperature of the domestic
water, the volume of the water increases.
The
additional volume created by thermal expansion must be
accounted
for. If the additional volume is not accounted for and hot
water
is
not being used, excessive pressure can build up within the systems'
storage tank.
High water pressure can compromise
the durability
(and the performance) of the system, potentially causing
the tanks temperature
pressure relief valve
to leak as well as shower
heads and faucets. A hot water heater expansion tank is the cost
effective solution to thermal expansion and high water pressure.
Temperature
Pressure Relief Valve and Thermal Expansion
The
temperature pressure relief valve is
a safety feature designed to operate as an emergency relief control and
not as a constant thermal expansion control. If the storage tank
pressure continually increases, it can cause the T & P valve to
operate frequently, which can ultimately result in the failure of the
valve.
Closed
Water
Systems
Many municipalities have back flow preventers or
check valves that are installed at the water meter. This means that in
most
homes today,
the water that enters from the municipal supply is prevented
from ever reentering.
In the past the additional water volume created by
thermal
expansion could flow back into the municipal supply, relieving
pressure. With the addition
of
back flow preventers and check valves, these homes now have closed
water systems.
Expansion
Tanks
and Plumbing Codes
The International
Association of Plumbing
and Mechanical Officials developed the Uniform Plumbing Code.
The
Uniform Plumbing Code, and many local building
and plumbing codes, require a storage tank to be equipped with
a
hot water heater expansion tank to control thermal expansion
in
closed water systems.
Unfortunately many existing homes with closed
water systems are not equipped
with expansion tanks. The same is true with new water heating
storage tanks. Often times thermal expansion tanks are not installed
during replacement, even though local codes often recommend thermal
expansion protection.
Manufacturer
Guidelines and Warranty
Many manufacturers of storage water
heaters
today recommend that expansion tanks be installed before high water
pressure is a problem. This is especially the case with gas powered
storage
tanks because the rate of thermal expansion is often greater than with
electric
powered tanks.
In many cases, failure to install a hot water
heater expansion tank
can result in the manufacturer warranty becoming null and void.
Necessary?
What's
Recommended
When installing a new storage tank water
heater, protect your investment and follow the manufacturers
recommendations. If the manufacturer recommends an expansion tank, then
install one regardless of local plumbing or building codes.
Homeowners with closed water
systems should check the existing storage tank and verify whether or
not
an expansion tank is present. If an expansion tank or a
pressure
reducing valve is not present, referencing the owners manual
or the local plumbing codes (with regard to
thermal expansion control) would be wise.
Homeowners with closed water systems and high
water
pressure exceeding 80 psi (when the heating element is activated and
water is not being used) should install a hot water heater expansion
tank, unless the manufacturers guidelines specifically recommend not
installing one.
Even if the manufacturer doesn't specifically
recommend installing an expansion tank, it's important to note that the
thermal control provided rarely compromises
the existing product warranty, and it will further protect the tank
from failure.
How
expansion tanks work
Water heater expansion tanks are
generally small and light
weight. These tanks often contain a pressurized internal
compartment
(often referred to as a bladder) along the bottom, and a polypropylene
lined internal compartment along the top. In most cases, in
between both
compartments is a flexible diaphragm.
When thermal expansion
occurs the additional hot water volume fills the internal compartment
along the top of the tank. As the pressure increases, the
flexible diaphragm compresses the pressurized bottom
compartment, making more room for the additional water volume.
Sizing
expansion tanks
Hot water heater expansion tanks are small, but
there available in several sizes. There are two important
considerations to make when sizing an expansion tank; the incoming or
supply water pressure and the volume of the storage tank.
Determining
Incoming or Supply Water Pressure
A homes' incoming water pressure is largely
determined by the local municipality or the local water source. From
mile to mile, the supply water pressure can vary
significantly. Determining a homes' supply water pressure is fairly
easy.
Pressure can be
determined by fitting a water pressure gauge on a faucet or an
outdoor fixture, 40 psi to 80 psi is generally considered an
acceptable range. The local municipality can be contacted to
perform an on site evaluation as well.
Selecting the
Right Expansion Tank
In an
attempt to assist would be consumers determine which
expansion tank is best suitable, many
reputable manufacturers display sizing and selection guides
(as well as labels) on their products.
These
guides and labels are broken down by incoming or supply water
pressure and water heater storage tank volume. Many
manufacturers offer tanks that are internally pre pressurized
as well. In some instances, additional pressure can be added to
accommodate those systems with higher water pressure.
Expansion
tank installation
Installing a hot water heater
expansion tank is a relatively easy project. Detailed installation
instructions and guidelines are generally provided. It's always wise to
follow the manufacturers' instructions and guidelines as carefully as
possible.
Installation
Guidelines
Generally
a single tee plumbing fixture is required to install the
expansion tank on the existing water pipe. Some industry
professionals suggest using plumbing hangers as well for
additional support. This is especially the case in homes that have PVC,
or plastic, plumbing pipes.
Cold Water Pipe
or Hot Water Pipe Installation?
Most manufacturers recommend installing a hot
water heater expansion tank on the cold water supply pipe.
Some professionals suggest that installation
on the hot
water pipe is equally as effective.
Other industry professionals suggest that
installation on the hot water pipe can have adverse effects on the
longevity of the water heater expansion tank.
When in doubt, always
follow the manufacturers' installation guidelines.
Horizontal
Installation or Vertical Installation?
Many industry professionals recommend installing
expansion tanks on horizontal pipe runs if possible. With that said
many manufacturers insist a horizontal
or a vertical installation has no tangible effect on the amount of
protection the tank will provide. When in doubt,
refer to the manufacturers' installation guidelines.
More on water heater maintenance
- Water
Heater Maintenance; how to extend the life of an old or
recently purchased storage tank.
- Water
Heater Anode; periodically inspecting the sacrificial anode
rod is a maintenance procedure that protects the storage tank from
corrosion.
- Drain
Hot Water Heater; draining or flushing the storage tank
removes sediments that can compromise efficiency and volume.
- Water
Heater Drain Valve; inspect the drain valve on the tank for
potential leaks and drips.
Energy efficient
water heating
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