Tankless water heaters 101
Quick answer
Tankless heaters make hot water only when you need it, so they never run out. But a tankless is only as good as the gallons per minute it can produce: three showers on a unit sized for one means lukewarm water for everyone.
Tankless vs. Tank Water Heater (Complete Guide)
Cost
San Diego's mild climate is great for tankless, because the heater doesn't work as hard. But they're more complex, and installed they can cost 4 to 5 times as much as a storage tank. An existing tank hookup won't supply enough gas, tankless needs new venting, and some homes need a new gas meter and line.
Space and efficiency
Tankless units are much smaller than storage tanks, and only use gas or electricity while hot water is flowing. A storage tank keeps water hot around the clock.
Sizing
Add up the flow of everything running at once: a bathroom faucet is 3 gallons a minute, a kitchen faucet, a shower and an appliance 4 each. A shower, a faucet and an appliance together need at least 11 gallons a minute.
Then the temperature rise: the difference between incoming water and the temperature you want. In Southern California, ground water is near the average air temperature, so for a 110°F shower with 70°F water, the rise is 40°F.
Rather we did it?
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