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How to install gas water heater
22 easy-to-follow-steps for professional installation
 
Use 6 wraps teflon tape
White for water lines
Yellow for gas lines

Buy:
Teflon tape at Amazon

Buy:
Pipe wrench at Amazon
Channel locks

Resources:
How to remove rusted element


Buy:
Knipex channel locks
Irwin pliers
replace anode rod
Inspect anode each 2-5 years
Anode rod prevents tank from rusting
Buy:
Anode rods at Amazon

Resources:
Replace anode rod
How to maintain water heater

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Impact wrench at Amazon

Resources:
Replace anode rod
How to remove short water heater nipple
Water pressure gauge

Pressure gauge/ attach to water heater drain valve
Pressure over 80 psi can damage water heater and household plumbing
Buy:
Water pressure gauge
Temperature-pressure gauge

Resources:
Identify water heater valves
Troubleshoot water pressure
Automatic water heater shut off valve
Prevent flood
Automatic water shut off valve
Buy:
Water detectors at Amazon
Automatic water heater leak shut off at Amazon
Resources:
Leaking water heater/ steps
Pressure reducing valve
Pressure reducing valve
Pressure over 80 psi can damage water heater and household plumbing
Buy:
Pressure reducing valve

Resources:
Identify water heater valves
Troubleshoot water pressure
Sharkbite pressure gauge
Sharkbite pressure gauge

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Sharkbite pressure gauge

Resources:
Water heater valves

Water heater circulation system

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Grundfos at Amazon

Resources:
How to install recirculation system
COLD side Sharkbite flexible water heater connector
COLD side Sharkbite flexible water heater connector

Buy:
Sharkbite water heater connection
Braided water heater line
Stainless steel flexible connection

Resources:
How to install electric water heater
How to install gas water heater
Leaking water heater
HOT side Sharkbite flexible water heater connector
HOT side Sharkbite flexible water heater connector

Buy:
Sharkbite water heater connection
Braided water heater line
Stainless steel flexible connection
Braided water heater line
Flexible water heater connection

Resources:
How to install electric water heater
How to install gas water heater
Leaking water heater
' ... building codes recommend locations for installing gas water heater.'
"Codes discourage installation in bedrooms, bathrooms accessed through bedrooms, and rooms with AC units.
This ensures the occupants do not come into contact with dangerous Carbon Monoxide released by appliances powered by solid, liquid or gas fuels.
Codes also specify that water heaters should be installed in easily-accessible area for simplified replacement, observation, servicing, and maintenance.
For attic installation, the attic should have access wide enough to permit easy removal of the appliance. It should also be spacious enough to conduct inspections and maintenance tasks ... at least 30 inches in length and 30 inches in width.
Heater should have a shut off valve on incoming cold water line.
Other codes require mandatory TP valve on each heater. TP valve code
Some local codes require anti-siphon valve for bottom-fed heaters (where cold water enters tank at bottom instead of top)"
Do you need a permit to install gas water heater
Icon gas valve   
Gas water heater thermostats
"codes state that each appliance should be fitted with automatic temperature controls."
Temperature of water entering cold water supply to taps should not exceed 130°. If tank thermostat is set above 130°, then install mixing valve: Mixing valve installation
If tank is overheating or not heating correctly, then replace thermostat
Symptoms: Lockout where heater cannot fire up, or if pilot cannot be lit, cold water, uneven temperatures, very high temperatures, if TP is releasing water due to very hot water, etc.
Buy:
Gas water heater thermostats at Amazon

Resources:
How to replace gas water heater thermostat
Add another thermostat to water heater
Troubleshoot gas water heater
Select new water heater
Install gas water heaterLarger image Fig 2
Fig 2 shows general parts for gas water heater with older-style mechanical gas control valve.
Gas shut off, black pipe for gas, TP overflow tube, vent hood, hot and cold inlets etc
Basic parts for gas water heater

-Propane and natural gas are different:
Check for type of gas on label of old water heater. Propane: do not install below grade (in basement). Propane gas is heavier than air. Propane gas leak hugs floor and can fill basement with explosive gas.
Natural gas is lighter than air, and will rise, and installation is suitable below grade.
Odorant is added to both propane and natural gas. If you smell gas, leave house. Call gas company.

Water heater label-BTU rating: Check label on side of old heater, and buy same-similar BTU rating for new heater. Larger BTU rating will provide slightly more hot water. For example, for more hot, choose 40,000 BTU instead of 30,000, but be careful that gas supply can keep up and not starve other appliances. Typical residential tank water heaters will usually not cause a gas shortage, but add up total BTU demand of all appliances and compare with BTU rating on gas meter. Check that you have 1/2 gas line to water heater to ensure adequate fuel can reach burner. Higher BTU heater costs more per year to operate. Economy and conservation suggest lower BTU is better choice.

-Physical dimensions: Water heaters made after April 2015 are larger diameter because of thicker insulation added to meet DOE standards. Measure height and diameter if necessary. Water heaters over 55 gallon must be condensing type heater. Purchase price and cost of heaters larger than 55 gallon make this an expensive choice. Install 2 water heaters.
TP valve-TP valve location: Check if TP needs to be specific height. Important if overflow tube goes through a wall or cannot be moved. TP overflow tube must drain downward, and cannot tip upward.
Resources:
Water heater sizing calculation .pdf
Water usage data .pdf
Which is best gas water heater
Two water heaters
TP valve code
How to install gas water heater
AO Smith air intake/ arrestor screen
-If Air intake is located on bottom
: Applies to AO Smith, Kenmore, Whirlpool, State, Reliance, Craftmaster, GSW etc
Air intake on bottom is easy to clean.
Set 3-legged water heater on bricks so air intake screen, or flame arrestor screen, can be inspected and cleaned.

Resource:
How to clean air intake
Water heater air intake
-If Air intake is located on side of tank
Flame arrestor screenRheem, Reliant, Ruud, GE, Bradford White etc
Air intake on side of tank means that combustion parts have to be removed to clean air intake screen.

If arrestor screen becomes clogged with dust, the amount of air entering combustion chamber is reduced, and this slows draft going up vent pipe, which causes slow draft, vent odors, sooting, possible danger from incomplete gas combustion, and eventually causes combustion chamber to overheat, which trips FV lockout system. Repairs required. Keeping arrestor screen is important, so choose water heater with screen located on bottom of tank where it is easier to inspect and clean.
Air intake screen
Resource:
How to clean water heater burner

Ok for electric heater, but not gas
Avoid dust and dirty locations.
Dirty, dusty environments pose hazards for all gas appliances. Water heater air intake will clog, and shut down burner or cause FV lockout. FV lockout

Avoid stored chemicals
Do not expose water heater to stored chemicals, swimming pool chemicals, laundry equipment
Remove chemicals from same room as water heater.
-Chemicals corrode water heater parts and vent pipe. 'Spray propellants, cleaning solvents, refrigerants, swimming pool chemicals, calcium and sodium chloride, household bleach, waxes and process chemicals are corrosive at very low levels with no odor."
Manufactured home water heater air intake
Manufactured home/ Small un-vented closet/ Small home
Mobile home water heater is designed to draw air from underneath structure.
This ensures adequate air supply to support combustion, and allows water heater installation inside small closet.
Air intake must be kept clean, and no flammable vapors stored nearby.
Spec sheet illustration of air intake

Install electric water heater instead?
Note: any ordinary electric water heater can be installed in mobile home when circuit breaker box can support rated wattage. 4500 watt electric water heater = 10 gauge wire and 240volt 30 amp breaker Replace elements with smaller wattage 3800 watt electric water heater = 12 gauge wire and 240volt 20 amp breaker
4. Warranties are same across all brands
First year parts-tank-labor are covered for original homeowner and non-commercial installation
Must be installed by instructions shown in product manual. Cannot be installed for commercial purpose, or placed in damp, dusty environment etc.
Some warranty sellers cover labor for installing new heater during first year.
After first year, parts-and-tank are covered, but no labor. Some warranties are pro-rated on parts and tank, and do not give full coverage as unit gets older.

Main difference between 6 year 9 year 12 year is anode rod diameter, or sometimes 2 anode rods. Other difference can include drain valve, inlet tube, nipples, burner orifice and manifold door assembly, weight and durability of materials.
Generally you can convert 6 year tank into 12 year or 15 year by inspecting anode each 1-3 years, and maintaining tank as shown in product manual.
How to Replace-anode-rod.html
How to maintain water heater

Simple math comparison between 6 and 12 year heaters: if 6 year heater costs $550, and 12 year heater costs $800, the cost difference is $250. In exchange you get 6 years of extended part warranty, or $41 per year for longer warranty. Since a typical gas control valve costs $100 - $140 to purchase at retail (2016), the longer warranty might be best choice.
DIY resource: Gas valve resource

Extended warranty

Extended warranty should include labor.
Old sizing chart
Post 2015 heaters require high tech for sizes over 50 gallon
Take showers instead of bath. Save 10 gallons hot water each time.
To achieve same hot water consumption as previous heater without buying more expensive heater install 2 water heaters, cut consumption, maintain heater, turn up thermostat temperature


Resources:
Two water heaters
9 ways to save with water heater
Maintain water heater
How to adjust thermostat
Ways to increase hot water
Calculate first hour delivery
7) EF (energy factor) is not efficiency ... EF is a formula for finding efficiency
30-40-50 gallon heaters have EF .675 - (.0015 x V where V is tank gallonage).
So a small percentage of tank volume in gallons is subtracted from .675 to find the efficiency
50 gallon gas water heater has .60 efficiency when new.
40 gallon has efficiency of .62
30 gallon has efficiency of .63
How much does it cost to run gas water heater?
Repair tankless water heater 8) Avoid tankless promotion
Typical family, tankless save $1-8 on monthly energy bill, but installation, maintenance, repairs and purchase price never payback. Tankless are maintenance heavy.
All costs are energy. Read1 Read2
Tankless require yearly maintenance, tank-type require periodic maintenance
9) KEEP IT SIMPLE: Expensive water heaters will not pay pack
Review GE Hybrid
Things you should ask before buying solar water heating system
water heater safety precautions
Cautions:  
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.

Safest practice: Gas water heater should be set 18" above floor level. Adequate incoming air supply is needed.
Do not install GAS water heater on top of carpet. Must be on wood or metal surface.
 
Keep household and building materials 6" away from front; 0-1" away from side and back; and 24" away from top of water heater.

Buy:
Water heater stand

Resources:
    Do not install LP gas water heater below grade (in basement).
Read water heater safety precautions before starting
Water heater precautions/ pdf
How to solder copper pipe Remove flammables away from water heater
Explosion inside your home wastes precious fuel, and could burn down neighbor's garage.
FVIR water heaters are NOT 100 effective for protecting home and life from explosion.
Do not set gas water heater on carpet or near flammables.
Ok for electric, but not gas

Buy:
Gas safety cans at Amazon
Resources:
Read about FVIR (flammable vapor retardation)
Installation starts here

Cold side has shut off
Run water and feel which pipe is hot

1) Identify hot and cold sides
Look for markings on top of old tank. Letters H and C are usually stamped into top of tank.
Water heater must be connected Hot-to-hot and Cold-to-cold.
Shut off valve should be located on Cold side. But never ASSUME... always check Hot and Cold sides.
Identify Hot pipe: run hot out of tap for a minute and use hand to check temperature of pipes on top of heater.

1) Turn off water Notice that shut off valve is located on COLD water pipe.
Hot pipe must go to side of heater marked HOT, and cold to COLD or heater will not work.
Disconnect water pipes from water heater.
If you are unsure which pipe is hot, then run hot tap for a minute and feel which pipe on top of water heater is hot
water key No shut off valve
Shut off water to house
Rotate shut off 1/4 turn so valve is perpendicular across water line

Located water meter box, remove lid, dig away dirt to find shut off
Shut off is located on house-side of meter
Use water key or pipe wrench

Buy:
Water keys at Amazon
clean out water heater tank
Drain water heater
2) Drain old water heater using valve at bottom of tank. Air must enter tank to drain water. Open TP valve or open tub faucet on hot side.

Install new heater so hose can connect to drain valve
If drain valve drips, use hose cap to stop drip
Flush open water heater
Water-heater-will-not-drain?
Turn off gas valve
Turn Gas valve OFF
Larger image
Gas valve is ON


3) Shut off gas

Locate gas line.
Gas line is black-colored metal pipe or a yellow-colored flexible tube.
Follow gas line back a few feet away from water heater and find gas shut-off.

When gas is ON, handle is positioned same direction as gas line.
Turn gas OFF, rotate shut off handle 1/4 turn.
When shut-off handle is perpendicular across gas line, then gas is off.
gas line to water heater
Keep end of pipe clean
4) Disconnect gas line from control valve using crescent wrench or pipe wrench.
Keep end of gas line clean. It is OK to reuse old gas line.
It must be kept clean. Carefully remove old sealant with clean rag ... do not get dust, debris, teflon tape, pipe sealant, water or anything into gas line. Any debris or moisture that enters gas control valve will cause malfunction of gas control. A gas control has internal valves, small carefully sized ports, wires and electromagnets that will fail if not clean.

If you have flexible gas line, take care not to twist or kink tube so you can use it again.
Note size of gas line: If you buy same BTU heater, then gas line is correct size.
If you buy heater with more BTUs, check that gas line is large enough.

Tip: Home center sells yellow-colored flexible gas line.
Back of flex-line package has BTU chart to help select correct size gas line.
New flex gas line can cost about $30 so use old one when possible.
Buy:
Knipex channel locks
Irwin pliers
sediment trapBlack pipe, and sediment trap
Yellow approved gas line and black pipe are acceptable materials for gas line.
Galvanized pipe is NOT acceptable: chemicals contained in gas will reacts with galvanized, causing flakes to come off pipe and enter gas valve, resulting in gas valve failure.

3" sediment trap is necessary to catch moisture, debris etc so the gas line stays clean.
No action is needed if sediment trap is present.
If pipes are very old, consider installing fresh sediment trap.
Use yellow approved sealant or yellow teflon tape.
Do not add any sealant or tape to last two threads of any gas line.
Black pipe union
Black pipe union
Keep pipe clean
Union
Gas line, and water lines can be connected with UNION. Use black pipe for gas.
Loosen large nut. Take apart union using two wrenches.
To re-install union:  Clean connection surface with rag and apply thin film of approved pipe sealant to each surface using finger to help pick up last bits of debris and to help seal pipe.
No teflon tape needed on threads of big nut.
Thread sealant must be rated for gas... read product label. Apply sealant to beveled surface of union.
Apply thread sealant completely over the surfaces that will connect together when union is reattached.
Keep parts clean so debris does not enter gas control valve
-or- replace union with flexible gas line.
Disconnect vent pipe
5) Disconnect vent pipe from draft hood
Support vent pipe with wire so it will not fall down.
Flue pipe joints should have 3 sheet metal screws at each joint.

Purpose of vent pipe is to remove combustion gases from house
Flue pipe hazard 6) Inspect vent pipes/ Do not use aluminum vent pipe
Vent pipe must be approved material as shown in product manual. For example galvanized or stainless steel or PVC.
Aluminum vent pipe is not code, and is unsafe for gas appliance vents. Use aluminum on dryer only.. never for water heater.
Install 3 sheet metal screws per joint, and then add metal tape over screws if required by local code.
Taping vent joints without using screws is not code.

If vent pipes are rusted, or covered with white condensate, or have holes, then vent pipes must be replaced.
If top of old water heater has black soot, that can indicate vent pipe is not working correctly. Danger.
A plumber may be necessary to correct vent problems.
Check that vent cover is still on top of vent pipe located on roof and that vent pipe has no obstructions and rises high enough above roof to meet installation specs shown in manual, and that it rises high enough from roof to exceed expected snow fall or ash build-up from local forest fire or volcano.
Read more about vents near bottom this page.
Resource:
Troubleshoot water heater vent
Test water heater vent pipe 7) Check if vent has proper draft by lighting match

See if smoke drafts immediately upward.
The smoke should not linger. It should draw upwards quickly.
If vent does not have draft or if furnace vent is blowing out of water heater vent each time furnace turns on, then vent pipes must be repaired.
Turn on all vent fans, and blowers going to outside, including gas furnace, whole house vent fans, bath fan, range hood fan, etc, and recheck the vent pipe draft.
Bad water heater draft can cause backdraft where toxic byproducts travel down vent pipe, entering home  ... this causes poison CO gas to enter house (instead of poisoning the air outside) ... symptoms of vent problem can be soot on top of old heater, soot on burner of old heater, frequent pilot outage, lazy yellow flame,  headaches that go away when leaving house, and death of occupants. Immediately contact plumber to solve the backdraft problem. Power direct vent water heater might be required if proper venting is not possible.

All gas appliances must vent out of house to avoid CO poisoning. Remove affected people from house, lay people on side and never on back, call for emergency assistance.
Read checking the draft
Convert electric water heater to solar
5. Do the vent draft test
8) Move old water heater out of way.

Resources:
How to remove water heater from attic

Re-purpose water heater
Recycle old water heater
Use old heater for solar water heater
Use old heater for tempering tank
Lift water heater into attic
How to lift heavy water heater into attic
Holly removing anode rod
Holly removes anode rod for periodic inspection Larger image
9) Identify anode rod location on new tank
Make sure anode can be accessed for removal and inspection.

Read manual to exactly locate anode rod on top of tank.
Some anode rods are 1-1/16" hex head
Other anodes are connected to hot water nipple.
Anode rods stop tank from rusting, are key for water heater lasting longer
Power vent models usually have anode port under the blower assembly
Resource:
How to replace anode rod

Hex anodes are standard 1-1/16"
Raise water heater 18" off floor
Larger image
Water heater stands at Amazon

Drip pan
Drip pan saves damage
See drip pan installation
Buy:
Water heater drip pans at Amazon
Buy:
Water detectors at Amazon
Auto-shut-off valve at Amazon
Avoid installing water heater where it is exposed to stored chemicals. Read about corrosive atmospheres

10) Set new water heater in place
Read manual for advisories.
Water heater should sit at least 18" off floor since flammable vapors, such as stored lawn mower gasoline and paint thinners, will gather close to floor.
Leave space so water hose can be connected to drain valve.
Water heater weighs 75-220 lbs empty. 40 gallon steel water heater filled with water weighs approx 400-500+lbs.

If area is prone to high water, set heater higher.
Warranty is void if water heater floods. Manufacturers recommend replacement of flooded heater. Do not touch water heater that has been flooded. Electric shock danger. Turn off breakers.

Use earthquake straps as required by code.
Earthquake straps at Amazon

Set water heater in drip pan.
If air intake is on bottom, then stand heater on bricks.
Drip pan cannot be deeper than 2", and must be 1-2" wider on all sides than water heater so the pan does not interfere with air supply entering water heater. Install 3/4" or larger drain connection that goes to a drain.
Many people don't use drain pan. Tank failure can render home unlivable until repairs are made. Leaking water heater
Water heater vent hood
Larger image
11) Connect draft hood to new water heater
2 or 3 sheet metal screws directly into top of heater
Install vent hood pdf from AO Smith

Gas water heater vent pipe
Attach vent pipe to draft hood using sheet metal screws.  See image
12) Attach vent pipe to draft hood using 3 sheet metal screws per joint, and then add metal tape over screws if required by local code.
Single wall vent pipe cannot be used for water heaters located in attics and may not pass through attic spaces, crawl spaces or any confined or inaccessible location. A single wall metal vent connector cannot pass through any interior wall.

Taping vent joints without using screws is not code.

Vent must fit over draft hood and be attached to draft hood with screws
See more images farther down on page.

Vent hood on new water heater and vent pipe diameter must match
3" vent hood
Most residential water heaters use 3" diameter vent pipe.
Some higher-BTU water heaters require 4" vent pipe
Some local codes require 4" vent.
Do not use 3" vent pipe on 4" draft hood. Larger vent is ok, but smaller is not. Electric water heaters do not require vent.
Buy:
3M Hi-temp silver flue tape at Amazon
solder 12a) Solder for copper water pipe
Use 95/5 tin-antimony solder or other equivalent when soldering copper water pipe.
Use non-lead solder
Do not use 50/50 tin-lead solder or lead-based solder for potable water lines.
Do not solder on connection that is attached to water heater nipples. Solder parts and then connect to heater.
How to solder pipe
Hot to Hot and cold to cold
Look for markings on top of heater
If water pipes are reversed, water heater will not work
Which is cold pipe? Cold pipe has the shut off valve

Use flexible copper for EZ connection
Buy:
Flexible water heater connection
c

Larger image
12c) Connect water pipes to new heater >> cold goes to side marked cold.
Hot to hot. If hot-cold pipes are reversed, water heater will not work.

Buy Di-electric nipple
Dielectric nipples at Amazon

Resource:
How to remove short water heater nipple
Use di-electric nipples so tank will last longer. Read more  Read
Buy new flexible copper or stainless water connector pipes at home center for easy installation of water pipes.
New copper or stainless flex connectors are recommended because old ones leak.
Heat trap pipe installation saves $2 per year.
Heat trap nipples provided by manufacturer can clog and cause low water pressure. Low water pressure   New water heater making noise

Copper ground wire added between hot and cold to avoid stray current corrosion.
Read about stray current corrosion
Reconnecting gas line: cautions
''Make sure piping is clean and free from scales and burrs.
Apply small amount of good quality pipe thread compound to the gas inlet of the control.
Use only AGA approved Teflon tape or Teflon pipe compound on gas inlet connection.
Teflon tape and compounds should be used sparingly on male threads only, leaving the first two threads clean. No teflon tape of pipe compound on first two threads..
Teflon tape or thread compound should never be used on female threads as it may be pushed into the control body, possibly causing the valve to stick or fail to close.
DO NOT OVERTIGHTEN.''

Use PTFE yellow teflon tape on gas pipe joints
14) Gas lines ... use yellow teflon tape
Connect gas line exactly as it was connected before.

      Apply yellow teflon tape, and leave first two threads clean with no tape.
Do not let dirt, stray teflon, or any debris enter gas line. Make sure gas line is clean.
If you can install water line successfully, you can connect gas line. Gas line has less pressure than water line.

When using pipe joint compound, use approved compound for gas. Do not over-dope pipe so compound can enter gas control valve.
Make sure inside diameter of pipe is clean and free of cuttings and loose dirt.

Don't overtighten gas line to gas control valve or damage to gas control valve can occur.
Do not overtighten connection at gas control valve
Just make it tight, but do not 'crank down' on the wrench or gas control valve can be damaged

You will perform a gas leak test on last step, so take it easy on the big big wrench when attaching pipe to gas valve.
Gas line connection
Do not overtighten
       Re-use yellow flexible gas line
If product manual requires solid pipe, do not use flexible connection.
For example hybrid, or tankless etc might require solid pipe so gas flow is maximum, and gas flow is not restricted by bends in pipe.
Local code might require solid pipe, otherwise flexible gas line is easier to install.
Do not use copper pipe for water heater gas connection. Gas will react with copper. There are regional exceptions that allow copper pipe, when the regional gas supply does not react with the copper. Check local codes.

Use yellow teflon tape on gas line connections
Home center sells yellow flexible gas line for easy installation.
Back of flex line package has BTU chart. Match flex-line diameter with BTUs of new heater.

3" drip leg (or sediment trap) is required to keep moisture and contaminates from entering gas control valve
Gas connection for water heater
Do not overtighten pipe at gas valve
      Use 'black pipe'/ do not use galvanized pipe for gas
Black pipe is for gas
Do NOT use galvanized pipe. Galvanized is reactive to gas.
Zinc flakes will come off galvanized pipe and enter gas valve causing malfunction.
Put yellow teflon tape on each pipe joint. Yellow-colored teflon tape is for gas pipes.
Do not overtighten pipe to gas control valve
Union and other black pipe joints can be very tight.
Re-install union:  Clean connection surface with rag and apply thin film of approved pipe sealant using finger to help pick up last bits of debris and to help seal pipe.
No teflon tape needed on threads of big nut.
Gas pipe capacity .pdf
water heater overflow tube
Install overflow tube
TP relief valve provides 2 in 1 protection against excessive pressure and excessive temperature in emergency conditions. Mechanical spring-loaded TP valve is reliable and fully automatic protection for hot water storage tanks and heaters.'

15) Install TP overflow tube
that runs down to at least 6 inches of floor.
Use pipe off old heater.
Overflow tube must be same diameter as valve discharge connection. Do not downsize pipe into smaller pipe. Overflow tube can have maximum 4 elbows and 30 feet length.
End of overflow tube cannot be threaded.
Tube cannot be lower than top edge of drip pan. Tube must terminate 6" above open drain. TP valve can draw water back into water heater if overflow tube is under water.
Do not cap off TP valve or obstruct overflow tube
Overflow tube cannot have shut off valve installed, or any obstructive valve
TP valve is first line of safety for water heater.
TP valve releases water when pressure or temperature is too high, and prevents possible water heater explosion
Resources:
How to test and replace TP valve
TP valve code
Install gas water heater Tank is installed
Water heater set 18" above floor in drip pan
 Vent hood and vent pipe connected with 3 screws at each joint. Aluminum tape over each joint.
Water pipes installed
Gas line connected to water heater control valve.
Overflow tube connected to TP valve

Next:
Turn on gas
Check for leaks
Fill tank with water
Turn on burner
Wall outlet surge protector
Type 3 surge protection outlet must be grounded
Wall outlet surge suppression/ protection for electronic gas controls and gas water heaters with blowers
Check product manual for electrical recommendation
Two outlets/ Both outlets surge-protected/ can also protect other outlets in the circuit
Meet standard for new water heaters that plug into outlet
Hot, neutral and ground wire needed/ can replace any ordinary outlet
Locate outlet within 10 feet of water heater ... do not use extension cord
Do not use GFCI ... can cause malfunctions, short-cycling with power vented water heaters.
Buy:
15 amp surge suppressor receptacle
Leviton J-box surge protection kit
15 amp duplex surge protector
Surge block
Resources
Types and installation for home surge protection
Outlet surge suppression manual
Surge protection outlet manual
15a) Water heaters that connect to electrical outlet.
If water heater has power vent blower etc, it will connect to electrical outlet.  Check product manual for electrical recommendation on surge protector. New gas valves and electronics can be damaged by simple power outage. Surge can happen when power turns off, then resumes.
  How to wire Whole house surge
Outlet must be wired correctly, with correct polarity and ground. See chart
Best result is dedicated outlet that does not connect to other circuits inside home, and does not have fluorescent lights on same circuit.
Use cheap circuit analyzer from hardware to test outlet. See image
Use multi-meter and test continuity between manifold tube on gas control and ground prong on plug.
Gas controls are damaged by surge: Use surge protector.
Troubleshoot power vent water heater
Gas valve is ON
Gas valve is ON
16) Turn gas ON
Rotate gas shut-off handle until parallel with gas line. This lets gas flow to water heater control valve.
Now that gas is ON: 
NO SMOKING, no flame, do not turn light switch on-or-off
OK to have lights ON, just don't turn ON any other electrical appliance until leak test is completed
You can easily smell gas. LP gas is heavier than air, so smell close to floor. NG is lighter than air and will rise.
Be prepared to leave house immediately if you smell gas.
LP gas falls to floor level, so smell close to floor. NG rises so you can smell NG leak when standing.
Do not worry excessively
Test for gas leak
Larger image
Give gas time to show bubbles.
Gas pressure is low, so it take time for leak to show.
17) Test for gas leak
 Leak test with main burner “OFF” and “ON”. Coat pipes and tubing joints, gaskets, etc. with a soap solution. Bubbles indicate leaks that must be corrected. DO NOT TEST WITH FLAME.

a) Test pipes: Mix liquid soap with water and use brush to put around around gas line joints to see if there are bubbles. Use plenty of soapy water. May take some time for bubbles to appear since gas is under low pressure.
Soap bubbles coming from joint indicate leak: retighten pipes, use teflon tape on yellow flex pipe and black pipe.
Do not overtighten pipes or damage can occur to gas control valve.

b) Test factory-installed connections located below gas control valve
Manifold and pilot tube connections located under the gas control valve do NOT use teflon tape.
See image of manifold and pilot tubes
If either tube under gas control valve is leaking, just tighten a little bit. Do not overtighten.
Manifold and pilot tube: look for reverse thread on LP water heater. Regular thread on NG water heater
Remember: Natural gas and propane gas both have less pressure on the line than water pipes, so gas pipes are easy to seal with ordinary wrench. If you can install water line without leaking, you can do the same with gas line. Do not over-tighten connections.
Gas odor will be present if gas line has leak. Smell close to floor since some gas can be heavier than air and will settle downward. If gas is present, leave house immediately and call gas company. Turn off main shut-off at gas meter.

Bathtub running full stream before lighting water heater
Tank must be full of water or steam explosion could occur!!

18) Fill tank completely with water until water is coming out of tub spout.
Open tub spout on hot side and wait for full stream of water.
Next open TP valve for a moment to bleed last of air from tank.
Turn off tub spout and light heater.
Tank cannot have any air when burner is turned on or damage can occur to tank.

How to light typical gas water heater
Read directions printed on side of your tank
19) Light new water heater as shown in water heater manual
Read product manual for tips and advisories.
How to light gas water heater by type of gas control valve
Keep combustible material away from gas appliance.
Make sure water heater is full of water before lighting pilot.
Test for gas leak before lighting heater, or activating pilot light.
Make sure that no raw gas is present in the surrounding area before putting appliance into operation.

After lighting heater, test for gas leak again using soap bubbles.

Note: New gas heater might have small water leak when first fired up because of condensation
Ignore a bit of water inside combustion area or bottom of tank.
This water is condensation and will disappear as tank reaches set temperature.
Any cold tank can show same condensation when fired up.
Water pipes should not be leaking.
Water should not be dripping down vent pipe: this signals bad venting or other vent problem.
Don't worry excessively, but if needed, post questions on professional water heater forum: The Tank
Test for gas leak 20 Test for gas leak again while burner is ON

Set temperature to 120 degrees
21) Adjust temperature to 120 degrees, or higher if family has more people.
Tank will heat 41 gallons per hour, so expect tank to be fully heated in an hour for example.
How to adjust water heater temperature
How to increase amount of hot water

Intelli-vent gas control valve and Honeywell Gas control valves are increasingly common
Water heater manual 22) Save water heater manual like gold.
Read everything in manual.
Record date of purchase and warranty period
Follow maintenance schedule and installation, operation advisories
Manual will save money and heater will last longer.
Read 9 ways to save with water heater

Installation is complete

Maintain water heater and it will last many years beyond warranty. Read manual and links below.
How to maintain water heater
    1)  Read about anode rods
    2)  Read about stray current corrosion
    3)  How to flush water heater
    4) Inspect for leaks
    5)  9 ways to save with water heater
    6) Water heater safety precautions
    7) Read manual and follow maintenance schedule and precautions
Test water heater ventHow to test water heater vent.
Let main burner operate for 5 minutes.
Then put match near vent hood.
Smoke from match should get sucked into vent
Water heater vent test/ pdf
Checking the draft
Read more at Tank
Attach vent hood to water heater
Flue pipe safety
See larger

During typical water heater combustion, hydrogen content of fuel is burned and the result is hot gases. One of these hot gases is steam or water vapor. Adequate venting or air draw up vent is required so gases vent outside. 
When there is inadequate draw, the water vapor cools and condenses on inside wall of vent pipe. This condensation water is acidic (pH 3-5) and corrosive. It will corrode steel metals and other materials.
Improper venting causes water to drip down vent into combustion chamber of gas water heater. Parts inside combustion chamber rust. Holes develop in bottom of water heater. Inspect combustion chamber for rust and water.

If steel vent pipe is not venting, the vent pipe will rust and get holes, or joints will fall apart. This situation causes hot gases to enter home and poses serious risk of odorless CO poisoning.

Simple test for proper venting: Pipes are not rusted or covered with white condensate. No water on top of tank. Burner inspection does not show excessive rusting. Light match under vent pipe and see if smoke immediately draws upwards. If smoke does not draw, then call plumber.
Flue Pipe Safety
Read manual for flue pipe clearances so hot vent pipe does not touch or come near combustibles.
Rusted flue pipe -or-water on top of gas water heater could indicate serious problem.
Call a plumber if you are uncertain.
Check pipes and flexible connectors for leaks.

If water coming from flue pipe:
1. Vent cover could be missing > rain water entering flue (replace cover)

2. Flue pipe clogged with bird nest or come apart or damp from improper venting: danger of odorless Carbon Monoxide poisoning

Serious danger from CO poisoning, a plumber should be called if you are uncertain about vent pipe water leak
Read troubleshooting at forum
See u-tube video
Read about CO detector

Glass lined steel water heater
How to replace anode rod
Stick man pointing
Woo Hoo
How-to-troubleshoot-gas-water-heater.html
Click link for gas water heater resources including troubleshoot by type of gas control valve.

Troubleshoot electric water heater

How to install under-counter water heater

How to flush gas water heater

Troubleshoot electric water heater

9 ways to save with water heater

How to test elements
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