Tankless Water Heaters

Before considering which tankless water heater to purchase, it is important to verify the type of fuel source you will be using. Tankless water heaters come in electric, natural gas, and liquid propane versions. Select the fuel source for the water heater that corresponds to the fuel source that you have. Natural gas is commonly written as NG, while propane is written as LP.

Tankless heaters are sized based on the gallons per minute (GPM) they are able to produce. Each tankless heater has a GPM rating associated with it. The best way to size a heater is to determine the maximum flow rate that you'll have at any time. You can assume that each shower requires 2.5 GPM. You may also need to consider any appliances that use a lot of water such as certain types of dishwashers or washing machines. The chart on this help section labeled Tankless Heater Selection will give you a better idea of which heater you need.

Tankless heaters use less energy than traditional tank style heaters. Traditional tank type heaters sit with 40 or 50 gallons of hot water in them all day, this is known as stand-by loss. They are wasting energy keeping this water hot until someone needs it. Tankless water heaters produce hot water only when it is needed. By using less energy tankless heaters will save you a significant amount of money in the long run.

Many of the tankless water heaters qualify for the 2009 energy efficiency tax rebate. The rebate pays back 30% of the cost of the item plus installation costs with a maximum rebate of $1500. The heaters need to have and EF rating of .82 or higher, or a thermal efficiency of .90 or higher. Most of the units we carry qualify for this tax rebate.

Tankless water heaters are on-demand units that heat water as it flows through a heat exchanger rather than storing a set volume in a tank. Both gas-fired and electric models skip the standby heat loss that comes with keeping a tank full of hot water around the clock, since the burner or heating element only activates when a fixture calls for hot water. Contractors stock whole-house condensing and non-condensing gas units for full-home replacements, along with compact electric point-of-use models for a single sink, shower, or remote fixture that is too far from the main water heater to justify long pipe runs. A tankless unit's smaller footprint frees up floor space in mechanical rooms and closets, which matters on multi-family retrofits and tight utility spaces. Sizing runs on flow rate and temperature rise rather than tank capacity, so matching a replacement to gas line size and venting keeps an installation code compliant and callback free.

Subcategories

• Gas Tankless Water Heaters: Gas tankless water heaters draw from a home or building's natural gas or propane line and use a burner to heat water on demand, making them a common choice for whole-house installations and full water heater replacements. Condensing models capture extra heat from exhaust gas for higher efficiency and vent with PVC or similar plastic pipe, while non-condensing units need stainless steel venting rated for higher flue temperatures. Both configurations need a properly sized gas line and combustion air supply to fire at full capacity, which matters when swapping in a tankless unit for an older tank-style heater. Multi-unit buildings sometimes stack several gas tankless units together to cover higher simultaneous demand across multiple bathrooms.
• Electric Tankless Water Heaters: Electric tankless water heaters use resistance heating elements instead of a burner, which removes the need for gas piping or exhaust venting altogether. Smaller electric models serve a single point of use, such as a bathroom sink or remote shower, while larger whole-house electric units need a dedicated high-amperage circuit and adequate panel capacity. Because electric units do not vent combustion gases, installers can mount them in tighter spaces than gas models, including closets and under-cabinet locations. Panel capacity is the main constraint on whole-house electric tankless installs, since larger units draw significant amperage during operation.
• Point-of-Use Tankless Water Heaters: Point-of-use tankless water heaters mount close to a single fixture, cutting the wait for hot water at sinks, showers, or laundry connections that sit far from the main water heater. Compact electric models are the most common point-of-use option, since they do not require gas venting and fit inside a vanity cabinet or utility closet. Contractors often add a point-of-use unit as a supplement to a whole-house water heater rather than a full replacement, targeting one problem fixture instead of re-piping the whole building. Placement close to the fixture is what makes these units effective, since long hot water runs defeat the purpose of a point-of-use heater.
• Tankless Water Heater Parts & Accessories: Tankless water heater parts and accessories cover the isolation valve kits, venting components, condensate neutralizers, and water filters that keep a unit running and make service calls faster. Isolation valve kits let a technician flush scale out of the heat exchanger without disconnecting the unit from the water lines, which matters in hard water areas where mineral buildup is common. Condensing gas models need a condensate neutralizer to treat the mildly acidic condensate before it reaches a drain. Matching venting components and filters to the specific unit's manufacturer and model keeps warranty coverage intact.

Buying Guide

Choosing between a gas or electric tankless water heater starts with what utilities are already available at the installation site. A home with an existing gas line and proper venting clearance is usually a straightforward swap for a gas unit, while a location without gas service or with limited panel capacity may point toward an electric model or a point-of-use unit instead. Flow rate demand matters more than tank size when sizing Tankless Water Heaters, since the unit needs to keep up with simultaneous fixture use rather than store a set volume ahead of time. Cold climates raise the temperature rise a unit has to deliver, which can push a borderline gas unit into a larger size or a second unit for a whole-house install. Condensing gas models cost more upfront but usually run more efficiently and vent with lower cost PVC pipe, a consideration on longer vent runs. Electric point-of-use units solve a narrow problem, like a remote bathroom or an addition, without the labor of extending gas lines or venting through the building. Whole-house electric units need a hard look at electrical panel capacity before committing, since undersized service is a common reason a project stalls mid-installation. Replacement jobs should also confirm that gas line diameter and venting material match the new unit's requirements, since reusing an old tank heater's undersized gas line is a frequent source of underperformance.

Frequently Asked Questions

Can a tankless water heater run out of hot water like a tank model?

No. A tankless water heater heats water as it flows through the unit, so it does not run out the way a storage tank does. Output is limited by flow rate instead, meaning too many fixtures running at once can drop the water temperature rather than cut off hot water completely.

Do gas tankless water heaters need special venting?

Yes, and the venting type depends on whether the unit is condensing or non-condensing. Condensing units vent with PVC or similar plastic pipe because the exhaust temperature is lower, while non-condensing units need stainless steel venting rated for higher flue temperatures.

Is a bigger tankless unit always better for a whole-house install?

Not necessarily. Oversizing adds cost without improving performance if the flow rate and temperature rise do not call for it, so sizing should match the home's simultaneous fixture use and incoming water temperature rather than defaulting to the largest available unit.

Can an electric tankless water heater replace a gas unit without other changes?

Usually not without an electrical review. Whole-house electric units draw enough amperage that panel capacity needs to be checked first, and a dedicated circuit is typically required, so swapping gas for electric often involves more than a straight unit replacement.

What maintenance keeps a tankless water heater running efficiently?

Periodic descaling through an isolation valve kit clears mineral buildup from the heat exchanger, which matters most in hard water areas. Replacing water filters and checking condensate neutralizer media on condensing models are the other routine tasks that keep a unit performing at its rated efficiency.