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What is a flue damper heater?
Dampered
heaters have a motor-operated damper that close off the flue opening at
top of heater during standby hours when heater is not running. When
the heater is operating, the motor opens the damper, allowing combustion
by-product to vent up the flueway to outside. 3" or 4" galvanized vent is approved.
The danper motor is not a vent assist. The motor merely opens and closes a damper or metal plate that fits over flue opening.
Dampered heaters are designed to reduce amount of heat that is wasted up the
vent
pipe during standby because the flue opening is closed. This means more heat is contained
inside heater, improving standby efficiency when compared with ordinary atmospheric heaters.
Flue
damper heaters are for residential homes wanting water heater with
possible higher
efficiency compared with ordinary atmospheric heater. AO
Smith flue damper heaters
are for heating hot water only, and not used for space heating, or
mobile home or manufactured home applications that might require less
BTU, side connections for water, and possible air supply from outdoors,
or require direct venting etc. Types of water heaters
Water heater Efficiency
*Water heater efficiency is the combined thermal efficiency (percent of heat from burner that is transferred
into the water) and standby efficiency
of a heater (loss of heat through sides and top of heater), plus
estimate of electric power consumed during operation of heater.
In
case of AO Smith flue damper, the amount of power consumed by the 24
volt transformer located inside box above gas valve is very small.
Real-world efficiency of any water heater varies by BTU rating of burner,
type of heater (flue damper, power vent, atmospheric, condensing,
etc), type of fuel (natural gas or propane), elevation above
sea
level, thermostat setting, incoming water temperature, ambient air
temperature, air supply, condition of heater, number of
gallons
inside tank, etc.
Typically, 40 gallon heaters have
slightly
higher efficiency than 50 gallon since smaller tank has
less surface area ... which means lower standby loss.
AO Smith flue damper Efficiency
AO Smith 40,000 BTU 40-50 gallon flue damper heaters have EF .68-.70
according to AO Smith
.... note
that EF (also referenced as EUF) is NOT Efficiency.
EF is a formula for calculating efficiency, that requires subtracting
small percentage (.0015) of tank volume in gallons.
AO Smith flue damper heaters have EF .68-.70 2019 spec sheet ... which
translates to .64-.625
combined thermal and standby efficiency ....
indicating that 36-38% of energy is lost to surrounding air or vented
up flue pipe durning combustion. In addition to
lost heat, burning hydrocarbon fuels (gas, oil etc) spews toxic byproducts (CO2 etc) that are puffing
out of every vent stack across the globe.
AO Smith flue damper heaters with EF .68-.70 exceed the federal 2015 energy
standard that requires EF .67. See chart
Resources:
How much does it cost to run gas water heater
2019 version compared with earlier models
Older spec sheet vs 2019 spec sheet
Changes/ Improvements include different coloration (was white, now
gray), the wires
are less visible and less prone to external damage, option for
Ultra Low NOx burner ... possible
addition of the ez-to-clean debris filter
... while other differences if any, are unclear. The warranty is still
same 6 year.
Pre 2015 flue damper models had EF .67 while the 2019 model has
higher EF .70.... this improvement is without explanation since spec
sheets show same
dimensions and weights, meaning more insulation was not added? So how
did the efficiency change? 40,000 BTU burners still heat the same
amount of water ... the universe didn't alter the physics of water
heating.
In
2015 ... possibly in response to changes in the federal energy
requirements ... AO
Smith reclassified the flue damper from 'residential grade' to
'commercial-grade for residential' ...maybe to sidestep residential
grade energy standards so they could claim .70 EF?
. .. plus they added the sales
promotion of 'commercial grade parts for residential heater' ... and
certainly parts are mass-produced and used on different
models, probably including commercial and light-duty commercial heaters
...
... but old and new parts sheets for flue damper are the same
... including same
low NOx burner, FV sensor, 24 volt transformer, gas control valve,
sequence of operation, troubleshoot steps
etc ... with the exception that older spec sheet does not show Ultra
low NOx
model, and the NOx burner design and heat sensor are be different than earlier models.
No matter the specific differences between old and newer design, AO
Smith Flue Damper heaters are made well, they are reliable, do
not need extraordinary maintenance or repair, parts are
available from manufacturer, and
repairs can be DIY.
 6 year warranty
AO Smith flue damper warranty applies to: Single-family residential
installation
only.
6 year full replacement for failed Tank, and 6-year replacement
parts.
Water heater must be installed and maintained as shown in manual for
warranty coverage. Read product manual
For
example, if the air intake is clogged with dust from a shop
environment, clothes dryer, or sanding drywall
during a remodeling project ... then water heater will shut
down because heater cannot draw enough air to support combustion ...
then the debris filter located around bottom 1-1/2" of heater must be
removed and
cleaned ... or air intake cleaned from below with duster or compressed
air ... or burner taken out and air intake screen
cleaned from above with compressed air or duster ... this is required
for the heater to operate in the
environment where it was installed ... and is not covered by warranty.
Install
heater in clean environment, without any flammable vapors ... or
chemicals such as bleach and chlorine, spray paint, etc that will
corrode burner parts over time .... turn heater off when using
flammables to avoid potential irreparable damage to heater and or
explosion/ fire .... turn off heater when remodeling or house
cleaning or furniture moving to avoid stirring up dust, dirt etc.
NOx emissions/
Ultra Low NOx, Low NOx, and 'regular' heater specifications
NOx
is a greenhouse gas and can be reduced with the installation of a
burner that keeps temperatures below the threshold of NOx formation.
Regular water heaters that are NOT rated for NOx, will release
approximately 54
ppm per BTU.
AO Smith flue damper heaters are made in two versions: 40-50
gallon
models with Ultra Low NOx (14 ppm per BTU) and 40-50 gallon models with
Low NOx
(20 ppm per BTU) burners.
The low NOx version
also has 40-50 gallon short models.
Otherwise, all types have same efficiency, operating parameters, gas
valve, parts, maintenance, and installation. All have 6 year warranty
for residential installation.
Difference between Low NOx and Ultra Low NOx would be found in
replacement parts, some troubleshoot steps,
and amount of NOx greenhouse gas released per BTU.
Other
toxic byproducts released by burning hydrocarbon fuel include SO, CO,
CO2, and acidic water vapor. These byproducts remain unabated and
unregulated 2019.
DIY
Troubleshoot, maintenance and repairs
-AO
Smith has solid and useful DIY maintenance, part
replacement steps, error-codes and general troubleshoot instructions
contained in the product manual ... but AO does not post a
service
manual for the Flue damper series.
-Bradford
White does have a service manual (posted below) which is useful,
however their design is slightly different than AO Smith
...
-There are additional resources (posted above) for troubleshooting gas
control valve error codes, that apply to flue damper, or apply to other brands that use
same general type of
Honeywell gas control valve.
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First
Hour delivery is the
amount of usable hot water from one continuous draw
 40
gallon flue damper has first hour delivery 68 gallons
50 gallon flue damper has first hour delivery 83 gallons
Family of 6 or large oversized tub requires first hour 80 gallon
For more than 80 gallons first hour, a condensing heater or two water
heaters might be correct choice.
Most 40,000 BTU heaters have same/ similar first hour rating.
Recovery
is how
many gallons tank will heat in one hour at 60°F rise in temperature.
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2019/ Yearly cost numbers are for
comparison only
Actual
cost depends on variables including: Hot water usage, incoming cold
water temperatures, thermostat setting, elevation above sea level, age
and condition of heater, general maintenance, air supply etc.
1) AO Smith Ultra Low NOx Flue
damper heaters are rated EF .69-.70 when new.
Require electric outlet
2) AO Smith Low NOx Effex
high efficiency heaters are rated EF .70 when new.
Require electric outlet Resource
Review Effex water heater
3) Several models of power
vent heaters are rated EF .67-.70.
Require electric outlet and vent pipe(s) to outdoors Resources:
Typical power vent spec sheet
Power vent spec sheet
4) ^Typical off the shelf 40,000 BTU atmospheric
heaters are rated EF .60-.62 when new.
Does NOT require electric outlet. Resource:
Typical spec sheet
5) Typical condensing
heaters
that are installed in high consumption homes when more hot water is
required, have EF .80-.84, but the burner rating is 100,000+ BTUs (vs
40,000 BTU for flue damper), and
yearly cost is more, but the cost per gallon of heated water is less
because of higher efficiency.
Require electric outlet.
Resources:
Typical AO Smith condensing heater spec sheet
Review Polaris condensing heater |
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AO Smith heaters are sold under
other brand names:
American,
Lochinvar, Reliance, State, Craftmaster all sell AO Smith version flue
damper heater ... and at one time, Whirlpool
and
Kenmore, etc. Whirlpool no longer sells water heaters. Kenmore and GSW
and other brands sell AO Smith heaters or versions of AO Smith, but not
the high efficiency flue damper.
American, State and Lochinvar
high efficiency flue damper is same as AO Smith
Resources
Lochinvar-high-efficiency-flue-damper-spec-sheet/
pdf
Lochinvar-high-efficiency-flue-damper-part/
.pdf
Lochinvar-high-efficiency-flue-damper-manual/
pdf
Compare other brands to AO Smith
AO Smith flue damper has EF .70. Bradford White flue damper series has
EF .64-68, while Rheem flue damper models have EF .65-.69
Bradford White and Rheem manufacture different, but similar flue damper
heaters, that are also sold under other brand names.
Bradford White
is a recommendable Low NOx (not Ultra Low NOX) product with both 6 and
10 year warranty models, and similar, but slightly lower efficiency
than AO Smith reports for their models.
Rheem
is a recommendable Low NOx (not Ultra Low NOX) product with 12 year
warranty, with slightly lower efficiency than AO Smith reports. Rheem
is problematic for DIY homeowners wanting a manual that shows routine
maintenance, and part replacement like the AO Smith resources.
Resources:
Bradford-white-flue-damper-manual
Bradford-white-flue-damper-error-codes
Bradford-white-flue-damper-spec-sheet
rheem-flue-damper-spec-sheet
rheem-flue-damper-warranty
rheem-flue-damper-manual
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Flue damper heaters use WV4460 style Honeywell gas control valve
thermostat
 Note
the gas control has on-off switch that must be in ON position before
lighting heater.
Images on left and right are from older resources and may not be exact
replicas for 2019 flue damper heater.
Resource:
Troubleshoot electronic gas control valves
The
gas valve has internal circuit board that controls water heater
operation and issues status codes ... and error codes when parameters
exceed limit.
The gas control valve is connected to the flue damper via the 'wiring
harness' that plugs into bottom of gas control.
When
thermostat senses that temperature is below set point, it will start
the heat cycle... if thermocouple is sending small electric
current through the copper pilot tube to confirm that pilot light is
ON, then gas control valve will activate the flue damper and verify the
damper is drawing air supply before releasing gas into the manifold
tube down to the burner where ignition of fuel takes place.
ECO (Energy Cut Off) sensor located inside the gas control valve
thermostat
probe that extends into the water at back of gas valve, will shut
off the water heater if the water temperature exceeds 189°F high limit.
If water temperatures exceed the
high limit, then status light on gas valve issues 4 flashes.
Gas valve must be replaced.
Resource:
How to replace gas control valve
Flue damper water heaters will
automatically shut-off in event of following:
1.
The water temperature exceeds 189°F ... for residential water heaters
with the 160°F Honeywell gas valve thermostat .... commercial
gas
control valves look same but can have higher temperature range,
depending on model of water heater. 210° is maximum allowable for any
type water heater. Above 210°F risks violent steam explosion.
3.
Excessive combustion chamber temperatures ... typically caused by dirty
combustion parts, poor venting, bad gas control. Turn off gas control
valve and press button on resettable thermal switch (the TCO) located
on front of
combustion chamber. Relight heater.
4. The presence of flammable vapors. Read below about FV and FVIR
events.
"Clear fault and force unit to recycle for ignition
1. Turn temperature control knob all the way clockwise
2. Recycle power to the heater (both fan motor and gas valve)
3.
Rotate the temp knob all the way to the left, then back to the right.
You must cross the midline seven (7) times to reset the gas valve.
4. Unit should return to normal operations if all faults have been cleared and repaired. You will hear the fan motor come on.
5. Set water temperature to a safe setting of 120º or less."
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Installation:
-Flue damper heaters install like any ordinary atmospheric-vented gas
water heater, except needs 120 volt outlet
within 10' feet of water heater.
40 gallon: 152 lbs, Height 64-1/4" x width 20"
50 gallon: 167 lbs, Height to 63-1/2" x Width 22"
AO
Smith flue damper "water heater is certified for installation on a
combustible floor' ... otherwise do not set heater near flammables.
Keep adequate space away from front. Minimum of 24" of front clearance
for inspection and service.
Minimum 3" clearance on sides and back" Do not set heater against wall.
Typical 17" clearance on top of heater
 2017
... " FVIR certified gas water heaters can be installed on a
residential garage floor without the use of an 18-inch stand in
accordance with the National Fuel Gas Code, NFPA 54, ANSI Z223.1,
unless otherwise directed by State and Local code requirements."
However, an FVIR heater is not 100% foolproof ... the FVIR system
reduces risk, but doesn't eliminate risk ... why? because flammable
vapors can still be sucked into heater where they can ignite and cause
internal damage ... requiring part replacement or irreparable damage to
heater.
The risk of internal damage to heater is much less with a
stand ... why? because gasoline is the most common cause of water
heater related fires .... and gasoline vapors are heavy and will hug
the floor.
Also dust and dirt are more likely to clog air intake if
heater is set on floor. Clogged air intake screen will result in
shut-down ... also improper operation, overheated combustion chamber,
poor venting, CO poison hazard, requiring TCO reset, removal of
manifold assembly for cleaning screen and possibly cleaning all
combustion parts.
Safest and best practice: Gas water heater should be set 18" above
floor level.
-Cannot be installed in dusty dirty environment. Avoid exposure to
chemicals.
-Can use 3" or 4" vent/ Single-wall vent pipe requires minimum 6"
clearance between vent pipe and combustible materials
double wall requires no clearance
-Drip pan
recommended to prevent water damage. Maximum depth of drip pan 1-3/4".
Set water heater on bricks if pan is
too deep.
 -
1/2" gas line. Can use flexible yellow gas line. Sediment trap
required on all gas water heaters.
-Water pressure should be 40-60 psi.
Typical city pressure is 60 psi. Rural pressure tanks are typically set
at 60 psi, but lower pressure can improve life of pump, equipment and
fixtures.
-Pressure over 80 psi can damage any water heater ... and shorten life
of pipes, fixtures, appliances: check household
pressure using pressure gauge on water heater drain valve. For high
pressure, install
pressure reducing valve and expansion tank to protect heater and
plumbing.
Buy:
Water
pressure gauges
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 Power requirement
Requires 120 volt outlet within 10 feet of heater.
This is a proprietary cord that plugs into the 24 volt transformer.
Flue dampered heaters are powered by 24 volt transformer ... or power
supply. Transformer is
located above the gas control thermostat valve, inside the
transformer box.
Transformer must be plugged directly into 115-125 volt
3-prong outlet/ 15
or 20
amp breaker.
Cannot use extension cord.
Extension cords, plug-in monitors, surge modules, plug-in wifi controls
do not
provide 100% reliable connection, and cause failed ignition. Unplug
water heater to reset gas control.
Use
circuit
analyzer to check outlet polarity and grounding.
Surge protection is recommended
for all electronic devices including flue dampered heaters. A
surge protection outlet is recommended vs a plug-in surge module ...
surge outlet is correct choice for reliable electrical connection.
Buy:
Surge
outlet
Circuits
can have multiple surge protection devices. The closer the surge
protection is located to the electronics, the better it protects. No
amount of surge protection can protect from direct lightning strike.
Simple power outage and power resumption can destroy electronics.
Additional action can include unplugging heater and use on-off switch
located on gas control during power outage or severe lightning storm.
Do
not use GFCI, it can cause malfunctions, it is not necessary and not
required by code. GFCI can interfere with operation of all
power
vented, and flue dampered water heaters, both residential and
commercial.
+++
Rheem flue damper series "is factory installed with a 3-pin 24VAC
transformer. A 19 feet long length of wire is provided for easy access
to an outlet. Do not use an extension cord for powering this water
heater. If the supplied power cord is insufficient to reach a power
outlet, a 30 foot power cord assembly is available as an accessory.
Contact the
service department to obtain and replace the power cord assembly that
was shipped with the heater." Source pg 12 |
 FV
(flammable vapor) protection
 Modern
water heaters often have FV sensor located on front bottom of heater
that integrates into the gas control
valve via wire.
The FV sensor is first line of defense against flammable vapor ignition.
There are 3 conditions that cause FV lockout:
1) FV sensor is wet, dirty, or out of calibration and needs replacement.
2) FV detected gasoline vapors and shut down heater before the gas
vapors could enter combustion chamber: remove gasoline hazard,
disconnect power to heater, or turn off switch on gas control valve to
reset gas valve, and then relight.
3) FV detected flammable vapors that ignited inside combustion chamber
and likely damaged heater: replace water heater.
The FV sensor will trip if it senses gasoline vapors in the air. It
does not respond to other types of flammable vapors.
Research shows that gasoline is the most common cause of fire or
explosion caused by water heater. The FV sensor located on
front
of heater is first line of defense, and will shut down heater
immediately if vapors are detected ... assuming sensor is not dirty,
not wet, and tests within the 3,000-48,000 ohm range for correct
functioning.
 Note:
FV Sensor does not prevent ignition of
flammable vapors if they are sucked into the heater through the air
intake. If vapors are ignited inside the heater's combustion chamber,
the FVIR
System is designed to reduce (but not eliminate) the risk of fire and
explosion accelerating from the combustion chamber back into the
room. Read pdf
AO
Smith heaters have specifically designed flame arrestor screen
(which is also the air intake) located
on bottom of heater. The screen is designed to allow free flow of air
into combustion chamber but stop the acceleration of
flames back into the room. If the heater experiences high-heat ignition
of vapors inside the combustion chamber, the heater must be replaced.
If FV lockout occurs. Remove source of flammable vapor from area. Turn
gas valve switch to off to reset heater. If the lockout condition
continues, then open the FV compartment located on front of water
heater. Test and replace the FV sensor first. It might be faulty.
Otherwise, the gas valve might be bad, wiring damaged, or heater
damaged by flammable vapor event inside combustion chamber. Call for
service.
Buy:
Flammable sensor kit
Resource:
How FV sensor works
Flammable vapor testing
How to replace Honeywell gas control valve
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 Clean environment is essential
for reducing maintenance and repair
costs.
Installing heater in a shop environment, craft area, outdoor
installation, laundry room
etc. will shorten life of heater ... Install electric heater if clean
environment is not possible.
 Base ring filter and flame
arrestor screen
Water heaters draw air into the combustion chamber through the debris
filter or base ring filter, and then through the flame
arrestor screen into the combustion chamber where the air
supplies oxygen to support burning of fuel.
To protect this process, do not install heater in dusty dirty
environment.
Key feature for the FVIR system includes the base ring filter or debris
filter that should be cleaned yearly according to manual.
The base ring filter protects the
flame arrestor screen from getting
clogged with dirt, leaves etc, but does not
protect from build-up of
dust that can clog the screen.
If the arrestor screen is clogged, the heater might not burn fuel
completely, causing unburned gas to enter flue pipe.... or it can burn
the fuel but the slow venting of by-product will cause excess heat
inside the combustion chamber.
Symptoms include lazy yellow flame, sooting on burner and sometimes
sooting on top of heater, and a gassy smell inside home.
 The low NOx flue
damper series comes with a resettable TCO (thermal cut off) located on
front of burner door that will trip and shut down heater if
temperatures inside the combustion chamber exceed limit.
The
ultra low NOx model has thermal switch located inside combustion
chamber that will trip and need part replacement.
It allows the flow of air into the combustion chamber ... but in event
of vapor ignition inside the combustion chamber, the arrestor screen is
designed to stop the acceleration of flames back out through bottom of
heater.
The high heat caused by such ignition will trip the TCO, and likely
damage burner parts and possibly damage the arrestor screen so it will
not function correctly afterwards. Replacing damaged heater is
required.
Exposure to chemicals:
Do not expose gas appliances, including water heater to corrosive
chemicals ... even in trace amounts.
 Over time, the heater will stop functioning due to
damaged parts that
are not be covered by warranty.
Except for 'power direct vent' type heaters, do not install gas water
heaters in in businesses like "beauty shops, dry cleaning
establishments, photo processing labs" ... the advisory of corrosive
chemicals extends to common chemicals
found inside home like powered and liquid bleaches, refrigerant leaks,
swimming pool chemicals, WD40, household spray bombs, calcium chloride
(used
as salt to melt ice on driveways), water softening chemicals, muriatic
acid, glues, anti-static fabric softener, paint removers, etc.
"Propellants of
aerosol sprays and volatile compounds, (cleaners, chlorine based
chemicals, refrigerants, etc.) in addition to being highly flammable in
many cases, will also change to corrosive hydrochloric acid when
exposed to the combustion products of the water heater. The results can
be hazardous, and also cause product failure."
Halogen contaminated atmospheres may be the cause of external corrosion
of gas water heaters.
|
 Resettable TCO
(thermal cut off) located on front of combustion chamber of the Low NOx
model
If
combustion chamber overheats because of FV event or clogged air intake
...heater will shut down ... to reset gas control,
disconnect power from heater, then press TCO thermal switch and this
should reset water heater.
Before
relighting heater ... remove
flammable vapors from area ... increase amount of available incoming
air
supply ...also might be required to remove manifold assembly to clean
air intake located at bottom of heater... when doing this, also clean
combustion parts and perform required maintenance as shown in product
manual.
Today's gas water heaters have FVIR systems to prevent flashover or
explosion of flammable vapors, such as gasoline or petroleum-based
paints, that enter water heater
combustion chamber. FV system can also trip if water heater is not
maintained as shown in product manual, or air intake gets clogged with
dust.
Turn off water heater when using flammables such as contact cement,
shellac, varnish, petroleum-based solvents, etc.
Thermal
cut off for Ultra Low NOx heaters is typically
located
inside the special burner that is inside the combustion chamber.
This type TCO is not resettable and requires part replacement.
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 Parts, warranty, competitors
AO Smith rates their flue damper heater as 'Commercial
grade for residential,' with the promotion of commercial grade parts.
Are the parts
commercial grade?
-Parts are mass produced, and likely used on different models of
heater,
including 'light duty commercial,'
and 'commercial' grade.
-Earlier versions of the flue damper were sold as 'Residential grade,'
and the manual shows identical parts illustration... See earlier manual
-The warranty for the AO Smith flue damper is only 6 years,
while earlier
versions that were sold by Kenmore, had 10
year warranty ... -Competitors offer 12 year warranty for a
residential grade dampered heater.
Extended warranty on the AO Smith flue damper is probably available,
and
comparison with competitors does not take into account that
competitor's may limit choices by factoring extended warranty into a
higher price, to extract more money with the illusion of
offering more value.
Note the advantages offered by AO Smith:
-AO Smith has fairly
complete parts sheet for the Low NOx model (but not for Ultra Low NOx
that has a different burner).
-The manual shows basic part
replacement and has a good troubleshoot section.
-Homeowners can buy parts directly from AO Smith.
-AO Smith flue damper has higher efficiency than competitors models,
who offer a Low NOx version but not Ultra Low NOx. Rhee spec sheet .pdf
Note: the 'commercial grade for residential' heater is for residential
installation only ... it is not covered by
warranty if installed in a commercial application, or if installed in
damp or dirty environment.
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