Tankless Water Heaters
tankless water heaters heat water as it flows through the unit instead of storing it in a tank. A flow sensor fires the burner or heating elements when a fixture opens and shuts them off when it closes. Units are sized by flow rate in gallons per minute and by fuel type: natural gas, propane, or electricity.
The category covers whole-house gas and electric models, commercial gas units for high-demand buildings, compact point of use heaters, and the parts used to install and maintain them. Each group is built for a specific load, from a single lavatory sink to a restaurant kitchen. Wall-mounted units free up the floor space a storage tank occupies, and correctly sized tankless water heating systems supply hot water continuously as long as demand stays within the rated flow.
Tankless Water Heater Products
Each group of tankless water heaters below matches a fuel type, demand level, or installation task.
Residential Gas Tankless Water Heaters
Residential gas models run on natural gas or propane and are designed for whole-house service. Most residential units are rated up to 199,000 BTU/h, enough to supply two or more fixtures at once. A propane tankless water heater fits homes without a natural gas utility connection.
Commercial Gas Tankless Water Heaters
Commercial gas models are built for restaurants, hotels, offices, and other buildings with sustained demand. Some commercial tankless gas hot water heaters carry input ratings above 199,000 BTU/h, and several units can be connected in a manifold, or cascade, so capacity increases as more fixtures open.
Residential Electric Tankless Water Heaters
Residential electric models connect to 240-volt service and need no gas line or flue. Whole-house electric on demand hot water heaters typically draw from multiple dedicated circuits, so confirm panel capacity first. When comparing electric tankless water heaters for sale, match the kW rating to the required flow and incoming water temperature.
Point of Use Water Heaters
Point of use models mount under or near a single fixture, such as a lavatory sink or hand-wash station. Installed close to the tap, point of use tankless water heaters cut the wait for hot water, and smaller models run on 120-volt circuits. In addition and remote restrooms, they serve as tankless instant hot water heaters without extending the main hot water line.
Tankless Water Heater Parts and Accessories
Tankless water heater parts and accessories include the components that connect, vent, and service a unit: isolation valve kits, vent pipe and terminations, condensate neutralizers, recirculation pumps, and scale-prevention filters. Isolation valves let a technician flush the heat exchanger without disconnecting the water lines.
How Tankless Water Heaters Work and Where to Use Them
How They Work
When a fixture opens and flow passes the activation rate set by the manufacturer, often 0.5 GPM or less, a flow sensor signals the control board. The burner or elements heat water as it moves through the heat exchanger, and the board modulates output to hold the setpoint. Closing the fixture stops the heat source.
Condensing vs. Non-Condensing
A condensing tankless water heater adds a secondary heat exchanger that recovers heat from exhaust gases. This lowers flue temperature and allows PVC, CPVC, or polypropylene venting where the manufacturer approves it, and it requires a condensate drain. Non-condensing units vent hotter exhaust through stainless steel or other approved venting and need no drain.
Residential and Commercial Applications
In homes, whole-house units supply bathrooms, kitchens, and laundry, while point of use models serve remote fixtures. Commercial uses include restaurant dishwashing and food prep, hotel guest rooms, office restrooms, and retail or light industrial facilities, where manifold tankless water heaters handle peak demand and provide backup if one unit is offline.
Key Specifications and Planning Steps
Flow Rate and Temperature Rise
Add the flow of all fixtures that run at once, then calculate temperature rise: target outlet temperature minus incoming water temperature. A 120°F setpoint with 50°F groundwater requires a 70°F rise. Available GPM drops as the required rise increases.
Gas Input and Fuel Supply
Gas units list maximum input in BTU/h. Size the gas line to that input, the meter capacity, and the pipe length under the local fuel gas code. A 199,000 BTU/h unit often needs a larger line than the storage tank it replaces.
Electrical Requirements
Electric models list kW and amperage. A 27 kW whole-house unit draws about 113 amps at 240 volts, split across multiple breakers, so verify service capacity before ordering.
Venting and Location
Confirm the indoor or outdoor rating, clearances, vent material, and maximum vent length in the installation manual. Outdoor models remove interior venting but may need freeze protection in colder regions.
Maintenance
Scale reduces heat transfer and flow. Flush the heat exchanger with descaling solution at the interval the manufacturer specifies, more often with hard water, and clean the inlet filter screen.
Choosing the Right Tankless Water Heater
The first question for tankless water heaters, gas or electric, comes down to the utilities already on site. Gas models deliver higher flow per unit and suit buildings with existing gas service. Electric models avoid venting and gas piping but depend on available amperage. For one or two fixtures, a point of use unit is often simpler than a whole-house installation. Smaller demands may be covered by a 4 GPM unit, while larger homes and businesses typically need 8 to 10 GPM or multiple units. When replacing a 50-gallon storage tank, plan for the gas, venting, and electrical changes listed above.
Frequently Asked Questions
Where can I find tankless water heaters with gas, electric, and point of use options in one category?
This category groups residential gas, commercial gas, residential electric, and point of use tankless water heaters, along with installation and maintenance parts. That lets a contractor match the unit, venting, and valves for a job from one set of product groups.
What specs should I check before ordering a propane tankless water heater?
Confirm the unit is rated for propane or field-convertible, then check maximum BTU/h input, GPM at your required temperature rise, venting type, and indoor or outdoor rating. Size the propane supply line and regulator to the unit's full input.
Should I choose tankless water heaters, gas or electric, for a residential replacement?
Gas suits homes with existing gas service and higher simultaneous demand. Electric suits homes without gas or venting options, provided the panel has the required amperage. Choosing between tankless water heaters, gas or electric, usually comes down to available utilities and peak flow.
What is the difference between a condensing and non-condensing tankless water heater?
A condensing tankless water heater uses a second heat exchanger to recover exhaust heat, vents through approved plastic pipe, and needs a condensate drain. Non-condensing units vent hotter exhaust through stainless steel or other approved material. For retrofits, condensing models often simplify vent routing.
When does a point of use tankless water heater make more sense than a whole-house unit?
Point of use tankless water heaters fit single fixtures far from the main heater, additions, and hand-wash stations. They cut the wait for hot water without new supply runs. Whole-house units fit when several fixtures run at once.
What size tankless water heater do I need for two showers running at the same time?
Two showers at about 2 GPM each require roughly 4 GPM at your temperature rise. With 50°F incoming water and a 120°F setpoint, choose a unit rated for at least that flow at a 70°F rise, plus margin for other fixtures.
Do I need to upsize the gas line when switching from a tank to a tankless unit?
Often, yes. Tankless gas hot water heaters commonly draw up to 199,000 BTU/h, far more than a typical storage tank. Size the line to the unit's maximum input, meter capacity, and pipe length under the local fuel gas code.
What electrical service does an electric tankless water heater need?
Whole-house electric on demand hot water heaters typically run on 240 volts across multiple dedicated breakers. A 27 kW unit draws about 113 amps. Check the manufacturer's breaker and wire size requirements against available panel capacity.
Why does a tankless water heater lose efficiency over time?
Mineral scale builds up on the heat exchanger, reducing heat transfer and flow. Flush with descaling solution at the manufacturer's interval, more often with hard water, and clean the inlet filter. Isolation valve kits from tankless water heater parts and accessories make flushing faster.
How do I size a commercial gas tankless water heater for a restaurant?
Total the peak GPM of the dishwasher, prep sinks, and hand sinks, then size for the required outlet temperature. Many restaurants install several units in a manifold so capacity follows demand and service continues if one unit is down.
How do electric on demand hot water heaters work compared to a storage tank?
Electric on demand hot water heaters energize their elements only when flow passes the activation rate, heating water as it moves through the unit. A storage tank keeps a full volume of water hot and loses heat while idle.
Can I replace a 50-gallon tank water heater with a tankless water heater?
Yes, when the tankless unit is sized for peak flow at the required temperature rise. Plan for a larger gas line or added electrical capacity, new venting for gas models, and a condensate drain for condensing units.
What venting does a condensing tankless water heater use?
Condensing models typically vent through PVC, CPVC, or polypropylene pipe where the manufacturer approves it, since exhaust temperatures are lower. Non-condensing models require stainless steel or other approved vent material. Always follow the installation manual for length and terminations.
What parts and accessories should I have on hand when installing tankless water heaters?
Common items include isolation valve kits, vent pipe and terminations, condensate neutralizers, gas connectors, pressure relief valves, and scale-prevention filters. Recirculation pumps are added where fixtures sit far from the unit.
Can tankless water heating systems supply a hotel or multi-unit building?
Yes. Large buildings typically use multiple commercial units connected in a manifold, sized to peak simultaneous demand. Manifolded tankless water heating systems add capacity as fixtures open and keep hot water available during service on one unit.