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10 Best Tankless Hot Water Heaters
From leading brands and best sellers available on the web.
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Buying Guide for the Best Tankless Hot Water Heaters
Choosing a tankless hot water heater can feel a bit overwhelming, but it doesn't have to be! The main advantage of these systems is that they heat water on demand, so you'll never run out of hot water and you can often save on energy. To find the model that fits your household best, it's helpful to understand the main factors that affect performance, efficiency, and comfort. By focusing on a few key specifications, you can match a tankless water heater to your needs and enjoy reliable hot water for years to come.Flow Rate (Gallons Per Minute, GPM)Flow rate measures how much hot water the heater can provide per minute. This is important because it determines how many faucets, showers, or appliances can run simultaneously without losing water temperature. Values usually range from about 2 GPM (suitable for a single sink or shower) up to 10 GPM or even higher (for large homes or multiple uses at once). When picking the right flow rate for your home, consider how many hot water sources you'll likely use at the same time—like taking a shower while the dishwasher runs. Count up the estimated GPM you'll need during your busiest hot water periods, and look for a heater that meets or slightly exceeds that demand.
Energy Efficiency (UEF or EF Rating)Energy efficiency ratings (sometimes shown as UEF—Uniform Energy Factor—or EF—Energy Factor) tell you how effectively the heater converts energy into hot water. A higher rating means more efficient operation and lower energy costs over time. Ratings usually sit between 0.80 and 0.99—where numbers closer to 1.0 are best. If you're environmentally conscious or want to lower utility bills, look for heaters with higher efficiency ratings. However, efficiency should be balanced with performance needs; don't sacrifice necessary flow for a marginal gain in efficiency if your household needs more hot water.
Fuel Type (Gas or Electric)Tankless heaters are powered either by natural gas/propane or electricity. Gas units generally heat water faster and handle larger demands, making them ideal for bigger households or multiple bathrooms. Electric units are typically easier to install and fit smaller spaces, but may suit homes with lower hot water demand or if you don't have gas lines. The right choice depends on your home's setup: check your available energy sources and typical hot water needs before deciding.
Required Electrical/Gas SupplyEvery tankless water heater requires a certain amount of power or gas to work properly. Electric models need specific voltage and amperage—often higher than a standard outlet—while gas models need the right pipe size and adequate venting. This spec is vital because an insufficient supply can cause the heater to underperform or even fail. Before picking a heater, make sure your home’s existing electrical or gas infrastructure can handle the unit’s demands; sometimes upgrades may be necessary.
Temperature RiseTemperature rise is the difference between the water’s starting temperature and your desired hot water temperature as it leaves the heater. This spec is important because colder incoming water (common in winter or colder regions) means the heater has to work harder. Manufacturers typically list flow rates based on specific temperature rises. Know your area's typical incoming water temperature and ensure the heater can provide enough hot water at your desired temperature, even during the coldest months.
Size and Mounting RequirementsTankless water heaters are more compact than traditional tanks, but they still require space for mounting, ventilation (for gas), and access for maintenance. The size and installation location can impact your plumbing layout and how easy it is to access the unit for service. When choosing, check where you'd like it installed—like a closet, basement, or exterior wall—and ensure there’s enough room, proper venting (if gas), and accessibility.
Warranty and Maintenance NeedsWarranties help protect your investment in case anything fails. Tankless heaters normally have warranties for parts and heat exchangers, ranging from a few years to over a decade. Maintenance, like descaling (especially in hard water areas), keeps the unit running efficiently and might be needed annually. A longer warranty can add peace of mind, but also look for models with easily accessible components for simple maintenance. Consider your comfort with basic upkeep or if you'd prefer professional servicing.