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Best tankless water heater: how to choose the right one
By the VettedHeater team · Last updated October 23, 2026 · How we verify
The best tankless water heater is the one sized for how many fixtures you run at once, matched to the fuel your home already has, and installed to code. We don't test, score or rank products. This guide explains what to compare and where to check real specs.
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Quick answer
- Size by flow rate (gallons per minute) and temperature rise, not tank gallons. Tankless units typically deliver 2 to 5 gallons per minute (U.S. DOE Energy Saver, "Which Water Heater Is Right for You?").
- Gas-fired units generally give higher flow rates than electric ones (U.S. DOE Energy Saver, "Which Water Heater Is Right for You?").
- National cost guides put tankless at $2,100 to $4,000 installed (This Old House, "How Much Does Water Heater Installation Cost?" (updated 06/17/2026; cost data from The Home Depot)).
- In the City of San Diego, a tankless install needs a plan-required Plumbing/Gas Permit (City of San Diego, Plumbing/Gas Permit).
What to compare between models
| Factor | Why it matters | Where to check |
|---|---|---|
| Flow rate (GPM) at your temperature rise | Decides how many showers and taps can run at once | Manufacturer spec sheet; see our sizing guide |
| Fuel: natural gas, propane or electric | Sets install cost, venting and electrical needs | Our gas vs electric guide |
| Uniform Energy Factor (UEF) | The standard efficiency rating; higher uses less energy | ENERGY STAR product finder |
| Condensing vs non-condensing (gas) | Affects efficiency, vent material and the need for a condensate drain | Manufacturer spec sheet and your installer |
| Built-in recirculation | Can shorten the wait for hot water at far taps | Manufacturer spec sheet |
| Warranty terms | Heat exchanger and parts coverage differ by brand | Manufacturer warranty page |
Brands to compare
Many brands sell tankless units, including gas and electric models. We don't score them. Compare current certified models by UEF and flow rate in the ENERGY STAR product finder, then ask your installer which brands they install and service locally, since local parts and service support matter for repairs.
Is tankless right for your home?
DOE says demand water heaters can be 24% to 34% more efficient than storage tanks for homes using up to about 41 gallons of hot water a day, and most last more than 20 years (U.S. DOE Energy Saver, "Which Water Heater Is Right for You?"). The trade-off is higher upfront cost and possible gas line, venting or electrical upgrades (This Old House, "How Much Does Water Heater Installation Cost?" (updated 06/17/2026; cost data from The Home Depot)). See tankless vs tank for the full comparison, tankless cost for prices, and licensed tankless installers in San Diego.
Get a shortlist of licensed tankless pros
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Related tankless guides
- Tankless installation in San Diego
- Tankless water heater cost
- Gas vs electric tankless
- Tankless water heater sizing
- Tankless vs tank
FAQs
What is the best tankless water heater?
There is no single best unit. The right one delivers enough gallons per minute at your temperature rise, uses fuel your home already supports, and has a strong UEF rating. Compare certified models in the ENERGY STAR finder.
Is gas or electric tankless better?
Gas units generally deliver higher flow rates, per DOE. Electric units avoid venting but can need a large electrical service. See our gas vs electric guide.
How much does a tankless water heater cost installed?
Nationally, This Old House, using Home Depot data, puts tankless installs at $2,100 to $4,000. San Diego prices may differ.
Sources
- U.S. DOE Energy Saver, "Which Water Heater Is Right for You?" (checked October 23, 2026)
- This Old House, "How Much Does Water Heater Installation Cost?" (updated 06/17/2026; cost data from The Home Depot) (checked October 23, 2026)
- City of San Diego, Plumbing/Gas Permit (checked October 23, 2026)
- ENERGY STAR Certified Water Heaters (product finder) (checked October 23, 2026)