Undersink water heaters are a convenient way to get instant hot water right from your sink. They are compact, easy to install, and can provide hot water on demand without having to wait for water to travel from a distant hot water heater. But are they really as good as they seem? Here is an in-depth look at the pros and cons of undersink water heaters.
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How Do Undersink Water Heaters Work?
Undersink water heaters are installed under the sink and connected directly to the hot and cold water supply lines. They are powered by electricity and use a heating element to instantly heat water as it passes through the unit. The water is heated on demand, meaning hot water is ready when you need it without having to wait for it to travel from a centralized water heater.
Most undersink heaters have a small storage tank that keeps a small reserve of hot water ready at all times. However, the majority of hot water is heated instantly as it flows through the heater. Flow rates are typically around 1.5 gallons per minute.
Undersink heaters range in power from about 500 watts up to 1500 watts. Higher wattage means faster heating but also higher energy costs. The wattage needed depends on factors like your home’s water temperature and desired output temperature.
The Pros of Undersink Water Heaters
Here are some of the main benefits that make undersink water heaters an appealing choice for many homeowners:
Endless Hot Water
The on-demand heating of an undersink unit means you never run out of hot water. As long as the water supply is on, hot water will keep flowing. This makes them great for busy households where hot water demands might exceed a conventional tank water heater’s capacity.
Faster Hot Water
You don’t have to wait for hot water to travel from a distant central heater with an undersink unit. The water is heated instantly, so you get hot water significantly faster. This reduces wasted water from having to wait for hot water to arrive at the faucet.
Energy Efficient
Undersink heaters only heat water as needed, rather than maintaining a large tank of hot water ready 24/7. This on-demand operation is more energy efficient compared to traditional tank heaters which can lose heat over time.
Compact Size
With their small footprint, undersink heaters fit conveniently under most sinks and can be installed in tight spaces. This makes them ideal for small homes or remote sinks far from the central water heater.
Lower Upfront Cost
Purchasing and installing an undersink heater is typically much less expensive than installing a whole-house tankless water heating system. The upfront cost savings make them accessible to more homeowners.
Zoned Heating
Undersink heaters allow for zoned water heating by installing units only where needed, like in a remote bathroom. This is more efficient than heating water for the whole house.
Simple Installation
In most cases these units can be installed under the sink without major plumbing modifications. Many homeowners can handle installation themselves. Installation costs are minor compared to a whole-house system.
The Cons of Undersink Water Heaters
While undersink heaters have some clear advantages, they also come with some downsides to be aware of:
Limited Flow Rate
The small size and power limits the hot water flow rate from an undersink heater, typically to about 1.5 gpm. This may not be enough for applications with high hot water demands like filling a large tub.
Must Run Hot Water Faucet
Since they heat on demand, you must turn on the hot water tap and let it run for the heater to activate. You can’t just turn on the hot tap and expect instant hot water like with a recirculating system.
Higher Operating Costs
The electricity demands of continuous on-demand heating mean undersink heaters are more expensive to operate long-term than centralized tank heaters.
Temperature Fluctuations
Output temperature can fluctuate with varying incoming water temperature and flow rate. This means you may experience some temperature instability as you use the hot water.
Risk of Scaling
In hard water areas, the heating elements can accumulate scale over time and require descaling maintenance to keep operating efficiently.
Single Point of Use
They only provide hot water at a single sink rather than the whole house. You may still need a centralized water heater depending on your needs.
Output Temperature Limitations
Safety features typically limit the maximum temperature to around 120-140°F. This may be inadequate for some high-temp applications.
Key Factors to Consider
Here are some important things to keep in mind when deciding if an undersink water heater is right for you:
Your Hot Water Requirements
Consider your daily routine and hot water needs. Frequent use or high demand applications may exceed an undersink heater’s capacity. But for a single sink’s basic needs, it can work well.
Incoming Water Temperature
The colder your incoming water, the more power is required to heat it. Very cold supplies may limit the heater’s output.
Energy Costs
These heaters have higher electrical costs than centralized heaters. Consider the operating costs factored over the heater’s lifetime.
Existing Plumbing
Your existing plumbing must accommodate installing shutoff valves and connecting the heater. Old galvanized piping may need replacement.
Maintenance Needs
Factor in descaling and element replacement maintenance that may be needed over time. Check that the unit is accessible for maintenance.
Safety Features
Look for models with overheat protection and check they are certified to meet safety standards like UL 499/CSA C22.2 No. 64.
Installation Considerations
Proper installation is key to ensure your undersink heater works safely and effectively. Here are some important installation tips:
- Follow all local plumbing codes for permits and inspections.
- The unit must be securely mounted under the sink.
- Shutoff valves on hot and cold supplies are required.
- Use unions and flexible lines for easy disconnect if servicing is needed.
- Ensure electrical is properly sized and grounded.
- Connect overflow pipe to drain pan if included.
- Flush pipes thoroughly to clear debris before connecting heater.
- Seal connections tightly to avoid any leaks.
- Test thoroughly and check for leaks before leaving site.
Hiring a professional plumber is highly recommended, especially if you lack plumbing experience. Paying for proper installation is worth avoiding potential issues down the road.
Top Undersink Water Heater Models
Here is a comparison of some of the best undersink water heater models on the market:
| Model | Power | Tank Size | Flow Rate | Price Range |
|---|---|---|---|---|
| Bosch ES2.5 | 500W | 2.5 Gallons | 1.3 GPM | $250-$350 |
| EcoSmart ECO 11 | 1300W | 2.5 Gallons | 1.5 GPM | $150-$250 |
| Stiebel Eltron DHC-E12 | 1250W | 3.17 Gallons | 1.5 GPM | $350-$500 |
| Rheem RTE 13 | 1500W | N/A | 1.5 GPM | $250-$400 |
As you can see, there is a range of power levels, tank sizes, flow rates, and pricing available. Consider your needs and compare specs to choose the right model for your application.
Sizing Recommendations
Choosing the right power level is important for optimum performance. Here are some general sizing guidelines:
- 500-750W: Hand washing, single bathroom
- 800-1200W: Small apartment, light kitchen duties
- 1300-1500W: Medium household, light simultaneous uses
- 1600W+: Busy household, high demand applications
Also factor in your household size, incoming groundwater temperature, and typical hot water usage patterns.
Energy Efficiency Tips
Here are some tips to maximize efficiency and savings with your undersink water heater:
- Set temperature only as high as needed. 120°F is hot enough for most uses.
- Insulate hot water pipes to minimize standby heat loss.
- Use low-flow fixtures like faucet aerators to reduce heating demands.
- Limit simultaneous hot water use to stay within heater capacity.
- Turn off dedicated circuit breaker when away for extended periods.
- Have a plumber service and descale the heater annually.
- Replace heating element as needed per manufacturer instructions.
Safety Tips
Observe these safety precautions when using your undersink water heater:
- Check for leaks and immediately repair any issues.
- Don’t block access to reset button or cover the unit.
- Keep flammable products away from under the sink.
- Test GFCI outlet monthly and replace if faulty.
- Never activate the heater when dry or empty.
- Monitor for excessive humidity under sink that could cause corrosion.
- Turn off water supply and power if extended time away from home.
Conclusion
Undersink water heaters can be a convenient and cost-effective way to get hot water right where you need it. For moderate hot water demands at a single point of use, they present a useful alternative to centralized heaters.
Carefully consider your family’s needs and household water heating requirements before deciding if an undersink heater is right for you. Proper sizing and installation along with safe operation practices are key to getting the best performance and value from these compact heaters.
Used appropriately, undersink heaters can be an energy efficient and handy source of instant hot water for your busy home.