Inline water heaters are a convenient way to provide hot water directly at the point of use, such as under a sink or next to a shower. Unlike traditional water heaters that heat water for the whole house, inline water heaters only heat water as it passes through the unit. This on-demand design provides endless hot water without the need to store heated water in a tank. However, some people have concerns about the safety of these compact water heating systems.
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How do inline water heaters work?
Inline water heaters are installed directly into the water supply line. Cold water enters the unit, passes across an electrical heating element or gas burner, and exits the unit hot. The water is heated instantly, on demand, rather than being stored in a tank. This eliminates the standby energy losses associated with storage tank heaters where water cools over time while waiting to be used. Inline heaters provide hot water only when needed.
Inline electric water heaters use one or more electric heating elements to heat the water. The elements turn on whenever water flows through the unit. Electric inline heaters provide between 3-12 kilowatts of heating power and can raise water temperature by 40-60°F. They require a 240-volt electrical connection and are wired directly into the building’s electrical system.
Gas inline water heaters use a gas burner that ignites when water flows through the unit. Natural gas or propane can be used as the fuel source. The heat output of gas inline heaters ranges from around 40,000 BTU/hr for small models up to 199,000 BTU/hr for whole house units. Gas inline heaters require proper gas line sizing and ventilation to operate safely. Both electric and gas inline heaters employ advanced flow sensors, temperature controls, and safety shut offs.
Benefits of inline water heaters
Inline water heaters offer several benefits over conventional storage tank heaters:
- Compact size – Units are only 10-20 inches long and mount directly in line with pipes.
- Endless hot water – Heats water instantly, on demand, for as long as needed.
- Energy efficient – No standby losses since water is heated only when flowing.
- Lower operating costs – Use less energy than storage tank heaters.
- Easy installation – Installs directly inline with water lines. No water storage tank needed.
- Point of use – Provides hot water right where needed, such as a bathroom sink.
The combination of small size, instant endless hot water, and energy efficiency makes inline water heaters an appealing option for light commercial, residential, and even RV applications. Their on-demand delivery of hot water helps reduce water waste by eliminating the need to wait for hot water to reach fixtures.
Safety concerns with inline water heaters
While inline water heaters offer advantages, there are some safety considerations to be aware of:
Overheating and scalding
Because inline heaters can raise water temperatures very rapidly, there is a risk of scalding if the output temperature is set too high or fails to regulate properly. Most models have maximum temperature settings of 140°F or less to help prevent scalding accidents. Using pressure balancing or thermostatic mixing valves can also reduce scalding risks. Proper installation and temperature settings are key.
Electric shock
Electric inline water heaters represent an electrocution hazard, especially if improperly installed or grounded. Only a licensed electrician should install electric inline heaters. Ground fault circuit interrupter (GFCI) protection should be used as an additional safety measure.
Gas leaks and carbon monoxide
Gas inline water heaters can leak gas or produce dangerous carbon monoxide if not properly installed and vented. A gas leak can lead to fire or explosion. Only trained professionals should install gas appliances. Regular maintenance is vital. Using CO monitors provides an extra level of protection.
Thermal expansion
When water is heated, it expands in volume. In a closed plumbing system, this thermal expansion causes pressure to build within pipes. The pressure needs an outlet. Storage tank heaters have built-in thermal expansion tanks. Inline heaters require installing an external expansion tank if one is not already present.
Water hammer
The abrupt on/off heating action of inline heaters can cause water hammer, which is damaging pressure spikes in pipes. Water hammer is exacerbated by quick-closing valves. Installing water hammer arrestors is recommended to protect plumbing.
Safety features of inline water heaters
Reputable inline water heater brands include multiple safety features to help prevent accidents and failures:
- Pre-set output temperatures of 120°F or 140°F
- Temperature limiting valves
- High limit switches that disable heating if temperature exceeds set point
- Pressure relief valves
- Leakage current detection on electric models
- Flame failure devices on gas models
- Overheat cut-off sensors
- Advanced electronic controls
- Built-in diagnostics
Additional requirements include:
- Manual reset thermostats for recovery from unsafe temperatures
- Energy cut-offs to prevent continued heating during abnormal flow conditions
- Water pressure regulators
- UL safety certification of components
- CSA, ETLI, or other electrical safety certifications
When properly installed by a professional with adequate safety devices in place, inline water heaters are generally safe to use. Proper maintenance according to manufacturer guidelines is also important.
Choosing a safe inline water heater
Here are some tips for choosing a safe inline water heater brand and model:
- Select a reputable brand like Eemax, Bosch, Eccotemp, Marey, or Stiebel Eltron.
- Check that the heater is ETL/UL certified for safety.
- Choose an appropriate power level and voltage. Undersized heaters can overheat.
- Pick a temperature-activated flow model for better temperature control.
- Get the right size for the application. Whole house units must be very robust.
- Read product manuals thoroughly to ensure proper installation and use.
- Consider a thermostatic mixing valve for added scalding protection.
- Work with licensed electricians and plumbers for installation.
It’s also important to follow all local building codes and regulations when installing inline water heaters.
Maintaining inline water heater safety
Once an inline water heater is properly installed, there are ongoing maintenance activities that help ensure continued safe operation:
- Visually inspect for leaks or damage during normal use.
- Check water and electrical connections periodically for tightness.
- Clean inlet water filters according to manufacturer directions to prevent obstruction.
- Test temperature regulators annually and replace if needed.
- Have gas heaters serviced by professionals yearly or as recommended.
- Flush heat exchangers to prevent scale buildup.
- Replace heating elements as required.
- Always turn off power/water supply before any maintenance.
Also replace the heater immediately if it exhibits any unusual sounds, smells, or improper functioning. Following the manufacturer’s maintenance guidance helps keep inline heaters operating safely for their full lifespan.
Conclusion
Inline water heaters provide an efficient way to get instant hot water right where it’s needed. While very convenient, they must be selected, installed, and maintained properly to ensure safe operation. Reputable brands include multiple protective features, but homeowners should still take steps like:
- Choosing UL/ETL certified heaters
- Having professional installation
- Using thermostatic mixing valves
- Setting appropriate temperatures
- Routinely inspecting and maintaining the heater
Taking these precautions helps minimize any risks and allows enjoying the benefits of inline water heaters safely.