Can a tankless water heater be installed under a sink?

Installing a tankless water heater under a sink is possible but requires careful planning and consideration. Tankless water heaters provide hot water on demand without a storage tank, making them an efficient option for small spaces like under a sink. However, there are important factors to weigh before deciding if a tankless water heater is right for your under sink installation.

The Pros of a Tankless Water Heater Under a Sink

Here are some of the main benefits of installing a tankless water heater under a sink:

  • Compact size – Tankless water heaters are much smaller than conventional tank models, making them a viable option for fitting under a sink.
  • On-demand hot water – Tankless heaters provide hot water only when needed, eliminating the wait for a tank to heat up.
  • Efficiency – Tankless models heat water directly without storing water, which is more energy efficient.
  • Endless hot water – The continuous on-demand flow of tankless models provide unlimited hot water.
  • Lower operating costs – The increased efficiency of tankless heaters leads to lower energy bills.

The ability to install a water heater in a small under sink space while still providing a steady flow of hot water is the main appeal of going tankless.

The Cons of Installing a Tankless Water Heater Under a Sink

However, there are also some downsides to consider with installing a tankless water heater in this type of location:

  • Upfront costs – Purchasing a tankless unit costs significantly more than a conventional water heater.
  • Venting requirements – Tankless heaters require special venting to the outdoors, which can be difficult under a sink.
  • Flow limitations – Sink applications may not meet the flow rate requirements for activating tankless heaters.
  • Space constraints – Fitting tankless heaters, valves, and plumbing under a sink is a tight fit.
  • Professional installation – The complex venting and gas lines of tankless heaters make professional installation a must.

The increased upfront investment and the need for proper venting, gas lines, and space requirements are the main drawbacks to installing a tankless water heater in this situation.

Requirements for Installing a Tankless Water Heater Under a Sink

Due to the compact under sink space, you need to select the right size and type of tankless water heater model. Here are some key requirements to consider:

  • Small unit size – Select an appropriately sized compact tankless unit designed for tight spaces.
  • Gas-powered – Electric tankless heaters may lack the power needed, making gas models the best choice.
  • Venting capabilities – Ensure the model has adequate venting options for under sink installation.
  • Minimum flow rate – Choose a unit with activation flow as low as 0.5 GPM.
  • Low clearances – Opt for a model requiring minimal service clearances for easier under sink fitting.
  • Energy factor – Pick a highly efficient model to maximize energy savings.

Choosing a tankless water heater specifically engineered for compact installation with flexible venting, a low activation flow rate, and high efficiency is key to making it work under a sink.

Water Heater Venting Options Under a Sink

Proper water heater venting is critical for safety and performance. Venting for under sink tankless heaters requires careful planning due to minimal space. There are a few venting options to consider:

  • Direct venting – This vents exhaust gas directly through an exterior wall via a two-pipe system. One pipe brings in combustion air while the other vents exhaust gas outside. This avoids competing for indoor air.
  • Power venting – This uses a fan to assist in venting exhaust through plastic piping that can be routed to an outdoor location. The fan enables venting with smaller diameter pipes.
  • Single pipe venting – Some models can vent exhaust and bring in combustion air via a single pipe. The exhaust and inlet airflow do not mix.

The most compact method is using flexible single pipe venting, if permitted by codes and the tankless water heater specifications. Power venting also allows flexible routing through smaller spaces.

Gas Supply Requirements for Tankless

Gas supply is another critical consideration when installing a tankless water heater under a sink. Here are a few key requirements:

  • Gas line sizing – The gas line must be sized properly to deliver the BTU demand needed for the tankless unit’s maximum hot water flow capacity.
  • Regulators – Any regulators in the gas line must be adequately sized for the increased gas demand.
  • Shut-off valves – Easy to access shut-off valves are required on the gas supply line for safety and service.
  • Flexible connectors – Use flexible gas lines under the sink to connect to the tankless unit and allow it to be removed as needed for maintenance.
  • High gas pressure – If gas line pressure is too low, a booster pump may be required to increase tankless water heater performance.

Consulting with a qualified plumber is advised to ensure the gas supply system is designed specifically to handle the gas flow rate needed by the tankless water heater.

Water Connections for a Tankless Water Heater

Connecting a tankless water heater into the sink’s plumbing lines also requires special considerations.

Here are some guidelines for the water connections:

  • Hot and cold lines – The tankless heater will need inlet and outlet connections for both hot and cold water lines.
  • Bypass valve – This valve diverts water flow when the tankless unit needs service.
  • Connection size – Use the recommended connection pipe size stated by the tankless manufacturer.
  • Isolation valves – Install isolation valves to easily shut off water to the heater for service.
  • Backflow preventer – This device prevents reverse flow back into the water lines.
  • Unions – Use union fittings for easy connecting and disconnecting of water lines.

Getting the plumbing configured correctly will ensure optimal water flow through the tankless heater.

Electrical Requirements for Under Sink Tankless Installation

Electrical capabilities are another important consideration for under sink tankless water heaters:

  • Voltage – Select a unit that runs on the voltage power supply available.
  • Amperage – Ensure the electrical system can supply the amperage required by the tankless unit.
  • GFCI outlet – The heater should be plugged into a GFCI outlet for safety.
  • Cord length – Make sure the power cord will reach an outlet without stretching.
  • Manual switch – Have a manual on/off switch to disconnect power for servicing.

A qualified electrician can assess your electrical system capabilities and recommend any necessary upgrades to support the electrical demand of the tankless water heater.

Installation Cost for an Under Sink Tankless Heater

One drawback of installing a tankless water heater under a sink is the higher installation cost compared to a standard storage tank model. Here are some of the factors affecting the installation cost:

  • Tankless water heater unit – The under sink tankless unit itself will cost $200 to $1000.
  • Venting materials – Special venting pipes and terminations will add $200 to $500.
  • Gas line installation – Connecting new gas lines can range from $50 to $300.
  • Plumbing modifications – Installation labor for water connections can be $200 to $800.
  • Electrical upgrades – Updatingwiring and circuits can cost $100 to $250.
  • Permits – Plumbing and building permits can be $50 to $150 total.

In total, installing a tankless water heater under a sink often runs $1000 to $3000. Hiring a professional plumber is recommended due to the complexity, which affects the overall cost. The high upfront investment may pay off long-term through energy savings and endless hot water.

Maintenance for an Under Sink Tankless Unit

While tankless water heaters generally last up to 20 years, regular maintenance is key to ensuring longevity and efficiency. Here are maintenance tips for under sink tankless units:

  • Inspect inlet filter – Clean or replace any inlet water filters annually.
  • Flush heat exchanger – Flush mineral deposits from the heat exchanger yearly.
  • Clean burner – Inspect and clean the burner surface when needed.
  • Check gas supply – Confirm gas pressure and flow meet specifications.
  • Test operation – Verify temperature settings and performance.
  • Check vents – Ensure vents are clear of any obstructions.

Consult your owner’s manual for the recommended maintenance schedule. Trained professionals can best perform more complex maintenance tasks.

Conclusion

Installing a tankless water heater under a sink is certainly possible with careful planning and proper installation. The compact size can provide an efficient water heating solution. However, the higher upfront cost, venting challenges, potential flow limitations, and maintenance requirements make it impractical in some situations. Consulting with qualified plumbing professionals is highly advised before deciding if an under sink tankless heater is the best option for your specific needs and home setup.