How Does a Water Heater Work? Inside the Tank Explained by Viking's Plumbers
- Matt Littau
- 9 hours ago
- 5 min read
What's Happening Inside Your Water Heater Right Now?
Most homeowners don't think much about their water heater—until they step into a cold shower.
Yet your water heater is one of the hardest-working appliances in your home. It operates 24 hours a day, 365 days a year, heating and storing dozens of gallons of water while quietly supplying your showers, sinks, dishwasher, washing machine, and more.
Understanding how your water heater works can help you recognize potential problems early, improve efficiency, and extend the life of your system.
Let's take a look inside.
The Basic Job of a Water Heater
The purpose of a water heater is simple:
Take cold water from your home's water supply, heat it to a set temperature, and store it until you need it.
Most residential water heaters in Wisconsin store between 40 and 80 gallons of water and maintain temperatures between 120°F and 140°F.
Whether your system uses natural gas, propane, or electricity, the overall process is remarkably similar.
How Water Moves Through a Water Heater
When you turn on a hot water faucet, hot water leaves the top of the water heater and travels through your home's plumbing system.
As that hot water exits, cold water enters the tank through a component called the dip tube.
The dip tube extends near the bottom of the tank and directs incoming cold water away from the hot water already stored at the top.
This design helps prevent cold water from immediately mixing with the hot water supply.
Without a properly functioning dip tube, you may notice that your hot water runs out much faster than expected.
The Hidden Component Most Homeowners Never See...
The dip tube is one of the most important—and least understood—parts of a water heater.
Its purpose is to:
Deliver incoming cold water to the bottom of the tank
Maintain temperature stratification
Maximize hot water availability
Improve heating efficiency
When a dip tube cracks, deteriorates, or disconnects, cold water enters near the top of the tank, causing inconsistent water temperatures and shorter shower times.
Many homeowners mistakenly assume they need a new water heater when a failed dip tube is actually the culprit.
How the Water Gets Heated
Gas Water Heaters
Gas water heaters use a burner located underneath the tank.
When the thermostat senses that water temperature has dropped below the set point, it signals the gas valve to open.
The burner ignites and transfers heat through the bottom of the tank.
Heat then rises naturally through the water until the entire tank reaches the desired temperature.
A central flue running through the middle of the tank allows combustion gases to safely vent outside.
Electric Water Heaters
Electric units use heating elements positioned inside the tank.
Most systems contain:
An upper heating element
A lower heating element
The upper element heats the top portion of the tank first, ensuring hot water is available quickly.
The lower element then heats the remainder of the stored water.
Because electric systems do not rely on combustion, they operate differently but achieve the same result.
Why Sediment Is Your Water Heater's Biggest Enemy
If you live in Wisconsin, you've probably heard about hard water.
What many homeowners don't realize is that hard water can significantly impact the performance and lifespan of a water heater.
As water is heated, naturally occurring minerals such as calcium and magnesium separate from the water and settle at the bottom of the tank.
Over time, this creates a layer of sediment.
This buildup can:
Reduce heating efficiency
Increase energy consumption
Cause popping or rumbling noises
Slow hot water recovery
Shorten equipment life
In severe cases, sediment can create insulating layers that force burners or heating elements to work harder, leading to premature failure.
The Most Important Part You've Never Heard Of: The Anode Rod
If there is one component responsible for extending the life of your water heater, it's the anode rod.
The inside of a water heater tank is made primarily of steel.
Since steel naturally corrodes when exposed to water, manufacturers install a sacrificial metal rod—typically magnesium, aluminum, or zinc.
This rod intentionally corrodes before the steel tank does. Think of it as a bodyguard for your water heater.
The anode rod attracts corrosive elements and sacrifices itself to protect the tank.
Once the rod is depleted, corrosion begins attacking the tank itself.
Many water heaters fail simply because the anode rod was never inspected or replaced.
What Is an Expansion Tank and Why Do Some Homes Need One?
When water is heated, it expands.
In homes with closed plumbing systems, that expansion creates additional pressure.
An expansion tank absorbs this pressure and protects:
Water heaters
Faucets
Valves
Appliances
Plumbing fixtures
Without proper expansion control, excess pressure can contribute to leaks, fixture damage, and premature equipment wear.
Why Water Heaters Make Strange Noises
Many homeowners become concerned when they hear:
Rumbling
Popping
Cracking
Knocking
In most cases, sediment buildup is the cause.
Water trapped beneath mineral deposits becomes superheated and creates steam bubbles that collapse as they rise through the tank.
The result is the popping or rumbling sound many people hear.
While not always an emergency, these noises often indicate it's time for maintenance.
How Long Should a Water Heater Last?
Typical lifespan depends on several factors:
Water Heater Type | Expected Lifespan |
Standard Tank Water Heater | 8–12 Years |
Well-Maintained Tank Water Heater | 12–15+ Years |
Tankless Water Heater | 15–20+ Years |
Factors affecting longevity include:
Water quality
Hard water levels
Maintenance frequency
Anode rod condition
Installation quality
Household usage
Signs Your Water Heater Needs Attention
Watch for:
Inconsistent hot water
Rust-colored water
Water pooling around the unit
Reduced hot water supply
Higher utility bills
Unusual noises
Rotten egg odors
Fluctuating water temperatures
Addressing these issues early can often prevent more expensive repairs later.
The Bottom Line
Your water heater may sit quietly in the basement, utility room, or garage, but it's performing a complex job every day.
Inside that tank, dip tubes direct water flow, burners or heating elements generate heat, anode rods fight corrosion, and expansion tanks manage pressure—all while delivering the hot water your family relies on.
Understanding how these components work not only makes you a more informed homeowner, but can also help you recognize problems before they turn into costly failures.
At Viking Plumbing, we help Wisconsin homeowners maintain, repair, and replace water heaters every day. Whether you need a professional inspection, annual maintenance, or guidance on selecting a new water heater, our team is here to help.
Need help with your water heater? Contact Viking Plumbing today to schedule an inspection and keep your hot water flowing year-round.