Tankless water heaters use burners and heat exchangers to instantly heat water and deliver it through your pipes. This is in contrast to hot water tanks, which continuously heat and reheat large quantities of water.
With a tankless water heater, you heat water on demand; for this reason, they’re sometimes called on-demand water heaters.
What Is A Tankless Water Heater?
How Tankless Systems Differ From Traditional Water Heaters
Traditional water heaters are primarily composed of three parts: A thermostat, a water tank, and a burner. The thermostat measures the temperature of the hot water in the tank; as the water cools below the predetermined temperature, the burner activates, reheating the water.
Tankless water heaters, on the other hand, heat water directly in the pipes. As water travels through the tankless heater, a burner activates, warming a heat exchanger. The cold water passes through that heat exchanger and heats; when demand for hot water stops, the burner in the tankless heater turns off.
The Problem With Hot Water Tanks
A hot water tank (sometimes called a storage tank water heater) holds massive quantities of water: Anywhere from 30 to 80 gallons. That water touches the sides of the tank, which, in turn, touches the air outside the water tank.
The air in your home is, of course, much colder than the water in your tank. This draws heat away from your water heater – and away from the hot water inside it. The temperature drops. Your water heater immediately turns on, heating the water inside it to the right temperature. Then, slowly, heat leaks out again.
There are steps to alleviate this problem; you can, for example, insulate your hot water tank. Unfortunately, there’s no way around heat leeching from your hot water tank.
Looking for energy efficiency? A tankless heater is the way to go; you avoid all of the problems caused by the effect we described above, known as standby heat loss.
Benefits Of On-Demand Hot Water
Almost anyone who uses a hot water tank regularly has experienced the biggest downside of traditional water heaters: Running out of hot water.
Tankless water heaters don’t have that problem; as long as they’re properly rated to the water usage in your home, you will never run out of hot water short of a power outage.
Another key advantage of tankless water heaters is that they’re more energy-efficient. Hot water tanks have to reheat water frequently; every time they heat up water when it’s not needed, energy is being expended unnecessarily.
Tankless heaters heat water on demand, so fuel is only used when necessary. The result: Lower energy bills and a lower carbon footprint.
The Inner Workings Of A Tankless Water Heater
Step-By-Step Breakdown Of The Heating Process
The step-by-step heating process of a tankless water heater varies somewhat depending on the fuel source used; gas and electricity are both commonly used fuel sources for tankless heaters. Regardless of the fuel source, however, some steps remain the same:
- A hot water tap is turned on
- Cold water enters the heater
- A flow sensor detects the water and turns on the system
- Heat is provided:
- Through a gas burner connected to a heat exchanger for gas systems
- Through a heating element connected to a heat exchanger for electric systems
- Water circulates through the heat exchanger, heating it to the appropriate temperature
- The hot water is delivered to the faucet or appliance
- When the hot water tap is turned off, the tankless heater shuts down
This step-by-step process is something of a simplification; there are fans used to exhaust flue gases and intake fresh air, condensate drain lines, pressure relief valves, and other parts that keep the tankless heater working. In gas heaters, a secondary heat exchanger may also be used to draw heat from flue gases and heat the water a second time, saving energy.
How It Provides Hot Water Instantly Without A Tank
In truth, tankless water heaters do not provide hot water instantly; they provide it nearly instantly – an important distinction. Tankless heaters work quickly, but there will always be water between the tankless heater and your faucet or appliance. This means that when you turn on your hot water tap (which triggers the flow sensor to turn on the heater), cold water will come out first.
The reason that they don’t need a tank is quite simple: Our technology is much more sophisticated than it used to be, and we can now use flow sensors to trigger the activation of gas, burners, heating elements, and fans – and use those same sensors to turn off all of the above.
Gas Vs. Electric Tankless Water Heaters
How A Gas Tankless Water Heater Works
Gas tankless heaters use natural gas (or sometimes other gas fuel sources, like propane) to heat water. When the flow sensor triggers the unit to turn on, gas valves open and the gas begins to flow; it is then ignited (usually with an electric ignition system) in the burner. The burner then heats a heat exchanger, through which the cold water flows.
Many gas tankless water heaters also feature a secondary heat exchanger. Exhaust gases (including water vapour) are sent through pipes to the secondary heat exchanger, which draws heat from those gases to heat the water further. This process reduces the amount of heat the burner needs to produce. A consequence, however, is that the exhaust gases have less energy; as such, flues must be installed lower in the building for proper ventilation. Additionally, PVC pipes are needed, as these flue gases are typically more corrosive.
How An Electric Tankless Water Heater Works
Electric tankless water heaters are simpler: They heat water using an electric element. This makes them incredibly efficient. Here in Winnipeg, however, gas tankless water heaters may still be more cost-effective. Gas is incredibly good at producing heat, so the heating per dollar ratio tends to be better with gas heaters.
Pros And Cons Of Tankless Water Heaters
Tankless water heaters have a lot of pros:
- They’re extremely energy-efficient compared to tank water heaters, saving you money
- When properly sized, they provide enough hot water to continuously feed all of the hot water needs of a home
- They’re more environmentally friendly
- They take up substantially less space
- They have an excellent lifespan
There is, however, one big con to tankless water heaters: They cost more to install than hot water tanks. This cost can be offset by energy savings (and sometimes, government rebates). Additionally, tankless water heaters need to be replaced less often – a lot less often.
Tankless water heaters can last for 20 to 30 years, while hot water tanks typically last 8 to 15 years. The cost of a tankless water heater is often about twice the cost of a hot water tank, including labour. The lifespan of a tankless heater is about twice that of a hot water tank; however, that means the cost over time is usually about the same.
Of course, tankless water heaters are more energy-efficient than hot water tanks. This means that, for many households, getting a tankless water heater means saving money. Coupled with the convenience that tankless heaters provide, they’re a clear winner for many families.
Common Issues With Tankless Water Heaters
Like hot water tanks, tankless water heaters can develop problems over time; routine maintenance can help alleviate many of these issues. Problems include:
- Mineral buildup from hard water
- System overload if the water heater is not properly rated
- Blocked air supplies which prevent proper combustion in gas heaters
- Breakers switched off (tankless water heaters can only provide hot water when they are powered)
- Other issues, including fan malfunctions, ignition malfunctions, and more
One of the most common issues with tankless water heaters is the “cold water sandwich”. Remember: Tankless heaters do not heat water instantaneously. Imagine you take a hot shower immediately after a family member. There will be hot water in the pipe between you and the water heater – but the water in the water heater will still be cold. When you turn on the hot water tap, hot water will flow – followed by cold water, then hot water (once the water heater is properly heating the water supply).
The solution? Wait a bit if you feel hot water immediately; cold water is probably coming. Once the cold water has passed, hop into the shower!
Learn More About Tankless Water Heater Systems
Want to learn more about tankless water heaters? Thinking of getting a tankless water heater for your home? Looking for an expert’s thoughts on the gas vs. electric water heater debate?
Call Provincial Heating & Cooling. We’ll help you determine if a tankless water heater is right for you. We can also help you pick the right tankless water heater, decide between gas and electric, and even install, maintain, and repair your new tankless water heater.