If you have ever run out of hot water halfway through a shower, you may have wondered whether there is a better way to keep the hot water flowing. Tankless water heaters offer a different approach from traditional systems by heating water when you need it instead of storing a large supply in a tank.
So, how does a tankless water heater work? When you open a hot water faucet, the unit detects water flow and activates a gas burner or electric heating element. Cold water passes through a heat exchanger, where it is rapidly heated to the desired output temperature before traveling to the faucet or fixture.
Once you turn the faucet off, the unit stops heating water. This on-demand operation can reduce standby heat loss and provide continuous hot water when the system is properly sized for the property.
Here is a closer look at how tankless hot water heaters work and what San Diego homeowners should know before deciding whether one is right for their home.
What Is a Tankless Water Heater?
A tankless water heater is a compact system that heats water on demand. It is also commonly called an on-demand water heater.
Traditional tank-type water heaters maintain a supply of heated water inside a storage tank. Depending on the system, a conventional hot water tank may repeatedly use energy to maintain the water at the selected temperature, even when nobody is using hot water.
Tankless water heaters operate differently. Instead of maintaining a stored supply, the unit starts heating water when you open a hot water fixture.
We offer both gas tankless water heaters and electric tankless water heaters. The best option for a particular property depends on factors such as available utilities, hot water demand, electrical capacity, installation requirements, and the desired flow rate. Our tankless water heater installation team can help you compare options.
How Does a Tankless Water Heater Work Step by Step?
Although tankless systems contain sophisticated components, the basic process is relatively straightforward.
1. You Turn On a Hot Water Faucet
The process begins when someone opens a hot water faucet or starts an appliance that requires hot water.
Cold water begins moving through the plumbing system and into the tankless unit.
2. The Flow Sensor Detects Water Movement
A flow sensor inside the unit recognizes that water is moving through the system.
Once it detects the required flow, the water heater activates its heating components. This automatic process allows the unit to operate only when there is demand for hot water.
3. The Unit Begins Heating the Water
How the water is heated depends on the type of tankless system.
Gas tankless water heaters typically use a gas burner fueled by natural gas or propane. Electric tankless water heaters use an electric heating element or a series of heating elements.
The system transfers heat to the incoming water as it moves through the unit.
4. Water Passes Through the Heat Exchanger
The heat exchanger is one of the most important components in a tankless water heater.
As incoming water travels through the heat exchanger, energy from the gas burner or electric heating element raises its temperature. The system monitors conditions and adjusts operation to reach the selected output temperature.
The amount of heating required depends partly on the incoming water temperature and the desired temperature rise.
For example, colder incoming water requires the system to add more heat to reach the same output temperature.
5. Heated Water Travels to Your Fixture
After reaching the appropriate temperature, the heated water leaves the tankless unit and travels through the home’s plumbing.
You may still have a short wait before hot water reaches the faucet. A tankless system eliminates the need to maintain hot water in a storage tank, but it doesn’t eliminate the distance water must travel through the pipes between the heater and the fixture.
6. The Unit Shuts Down When Demand Stops
When you close the hot water faucet, the flow sensor detects that demand has ended.
The system then stops heating water until another fixture calls for it.
This operating cycle is a major difference between tankless and tank-type water heaters.
Gas vs. Electric Tankless Water Heaters
The basic idea behind gas and electric tankless water heaters is similar, but they produce heat differently.
Gas Tankless Water Heaters
Gas tankless water heaters use natural gas or propane to generate heat. When you request hot water, the burner ignites and heats the heat exchanger.
Because burning fuel produces combustion gases, gas systems also require venting. Correct venting is an important part of installation and safe operation.
Installation requirements vary by unit and property, so follow the manufacturer’s specifications and applicable codes.
Electric Tankless Water Heaters
Instead of combustion, electric tankless water heaters use electrical resistance heating.
Water flows past an electric heating element or multiple elements, which transfer heat to the water before it leaves the unit.
Electric models do not produce the same combustion gases as gas-fired units, but their electrical demands can be significant. Whether a property can accommodate a particular unit depends on the home’s electrical system and the heater’s specifications.
What Does Flow Rate Mean for a Tankless Water Heater?
Flow rate is critical when selecting a tankless water heater.
Tankless capacity is commonly discussed in GPM, or gallons per minute. This measurement tells you how much water moves through the system over a given period.
Every fixture contributes to total demand. If a shower, sink, and another hot-water fixture operate simultaneously, their combined gallons per minute determine how much hot water the heater must handle at that moment.
A properly sized system needs to accommodate the property’s expected simultaneous demand while producing the required temperature rise.
If demand exceeds the unit’s capabilities, performance may not meet expectations. This is why choosing a tankless water heater based only on household size can be misleading. Fixture demand, incoming water temperature, and required temperature rise also matter.
Can a Tankless Water Heater Provide Continuous Hot Water?
One of the most appealing features of tankless hot water heaters is their ability to provide continuous hot water within their operating capacity.
A traditional storage tank contains a limited volume of heated water. Once that supply is depleted, the system needs time to heat more water.
An on-demand water heater does not rely on a stored reservoir. As long as water continues to flow within the unit’s capabilities and the heater has the necessary energy supply, it can keep heating water.
However, “continuous” does not mean “unlimited capacity.”
Every tankless unit has operating limits. Running several high-demand fixtures at the same time can exceed the system’s available flow rate or heating capacity. Proper sizing is therefore essential.
Are Tankless Water Heaters More Energy Efficient?
Energy efficiency is one reason homeowners consider switching from a traditional hot water tank to a tankless system.
Storage systems can lose heat on standby because heated water remains in a tank while waiting to be used. An on-demand system avoids maintaining the same large reservoir of heated water around the clock.
Actual energy use and savings vary by equipment, installation, household hot water habits, fuel source, local utility costs, and other factors. The U.S. Department of Energy’s guidance on demand-type water heaters explains how those variables affect real-world efficiency.
For homeowners comparing systems, it is better to evaluate the efficiency specifications of individual models rather than assume every tankless unit will provide the same savings.
What Are the Benefits of Tankless Water Heaters?
Tankless water heaters can offer several advantages when selected and installed properly.
One is their space-saving design. Without a large storage tank, the equipment can have a much smaller footprint than a conventional tank-style system.
Another potential benefit is energy efficiency. Because the system does not continually maintain a tank full of hot water, standby heat loss can be reduced.
Tankless systems can also provide continuous hot water within their rated capacity, making them attractive to households concerned about depleting a traditional tank.
Lifespan can also matter when comparing water heaters, but actual service life depends heavily on equipment quality, water conditions, installation, usage, and maintenance.
What Are the Drawbacks of Going Tankless?
Tankless water heaters are not automatically the best choice for every property.
The upfront cost can be higher than replacing a conventional tank-type unit, particularly when the installation requires changes to gas lines, venting, electrical service, or other components.
Capacity also requires careful consideration. A unit that is too small for the property’s peak demand may struggle when several fixtures require hot water at the same time.
Installation can also be more involved when converting from a storage tank to a tankless system. A plumber should evaluate the existing setup and the proposed equipment’s requirements before determining what work is necessary. Compare it against a standard water heater installation before deciding.
Hard Water and Tankless Water Heaters
Water quality is an important maintenance consideration for tankless systems.
Hard water contains dissolved minerals that can contribute to mineral buildup inside plumbing equipment. Over time, deposits can accumulate in areas such as the heat exchanger and potentially interfere with efficient heat transfer or water flow.
Because of this, maintenance may include descaling the tankless water heater.
The appropriate maintenance schedule depends on the equipment manufacturer’s recommendations, water quality, and usage conditions. A professional can help assess the system and determine an appropriate service schedule.
In some situations, homeowners may also consider a water softener or other water treatment equipment. Whether that makes sense depends on the property’s water conditions and other factors.
Does a Tankless Water Heater Deliver Hot Water Instantly?
“Tankless” and “instant” are sometimes used interchangeably, but they do not necessarily mean hot water reaches every faucet immediately.
The heater starts operating when it detects water flow, but the heated water still has to travel through the plumbing between the unit and the fixture.
If the bathroom is far from the water heater, there may still be a delay before hot water reaches the faucet or shower.
The exact wait depends on the plumbing configuration and other installation-specific factors.
How Long Do Tankless Water Heaters Last?
The lifespan of a tankless water heater depends on several variables, including the model, installation quality, frequency of use, water quality, and maintenance.
Routine maintenance is especially important in areas where mineral buildup develops inside the system.
Rather than relying on a universal lifespan estimate, homeowners should consult the manufacturer’s documentation for their specific equipment and have the system evaluated if they notice performance changes.
Signs Your Tankless Water Heater May Need Service
Like other plumbing equipment, tankless systems can eventually develop problems.
Changes in water temperature, reduced hot water performance, unusual system behavior, error codes, leaks, or difficulty maintaining the desired output temperature can indicate that the unit needs attention.
Mineral buildup can also reduce performance over time, especially when routine descaling is neglected.
Some problems are relatively straightforward to diagnose, while others can involve gas, electrical, venting, water-flow, or internal component issues. Professional water heater repair can help identify the cause instead of relying on guesswork.
Is a Tankless Water Heater Right for Your San Diego Home?
Choosing between tankless water heaters and traditional tank-type water heaters requires more than comparing equipment prices.
Consider how much hot water your household uses, how many fixtures may operate simultaneously, available gas or electrical capacity, installation requirements, maintenance expectations, and upfront cost.
Also consider the required temperature rise and flow rate when sizing equipment. A unit that works well for one household may not suit another.
A professional plumbing assessment can help determine which type and size of water heater fits the property’s actual hot water requirements.
Get Help With Your Tankless Water Heater in San Diego
Understanding how a tankless water heater works is the first step. Selecting, installing, and maintaining the right system requires attention to your property’s details.
Trustworthy Plumbing provides plumbing and sewer services for San Diego residents and businesses, including water heater service. If you are considering a tankless system or need water heater repair, contact Trustworthy Plumbing to discuss your options.
Senior and veteran discounts are available.
Frequently Asked Questions About Tankless Water Heaters
How does a tankless water heater work?
A tankless water heater heats water on demand instead of storing heated water in a tank. When a hot water faucet opens, a flow sensor detects demand and activates a gas burner or electric heating element. Water moves through a heat exchanger, reaches the target output temperature, and travels to the fixture.
Do tankless water heaters run out of hot water?
Tankless water heaters don’t deplete a stored supply the way a traditional hot water tank does. They can provide continuous hot water while operating within their rated capacity. However, simultaneous demand can exceed the unit’s flow rate or heating capability.
What does GPM mean on a tankless water heater?
GPM means gallons per minute. It measures flow rate. When sizing a tankless water heater, consider the expected GPM from fixtures that may operate at the same time.
Do tankless water heaters use natural gas?
Some models do. Gas tankless water heaters can operate using natural gas or, depending on the model, propane. Other tankless systems use electricity instead of a gas burner.
Do gas tankless water heaters need venting?
Gas-fired tankless water heaters produce combustion gases, so proper venting is an important installation requirement. Venting requirements vary by equipment and installation, so follow the manufacturer’s specifications and applicable codes.
Do electric tankless water heaters have a heat exchanger?
Tankless systems transfer energy into flowing water rather than maintaining a storage tank. Electric units use electric heating elements to provide that energy, while gas models use combustion-based heating. Component design varies by manufacturer and model.
Does hard water damage tankless water heaters?
Hard water can contribute to mineral buildup within plumbing equipment. Scale accumulation can affect components such as the heat exchanger, which is why descaling may be part of tankless water heater maintenance.
Should I install a water softener with a tankless water heater?
That depends on water quality, equipment requirements, and the property. A water softener can reduce hardness minerals, but homeowners should evaluate their specific water conditions and follow the water heater manufacturer’s recommendations.
Is a tankless water heater more energy efficient than a storage tank?
Tankless systems can reduce standby heat loss because they do not continually maintain a large tank of heated water. Actual energy efficiency and operating costs depend on the specific equipment, usage patterns, fuel source, and installation.
What is the biggest consideration when choosing a tankless water heater?
Proper sizing is one of the most important considerations. Evaluate flow rate (gallons per minute) along with incoming water temperature, required temperature rise, simultaneous hot water demand, and the unit’s capabilities.