Two different ways to make hot water
A tank water heater keeps a set volume of water hot around the clock and refills as you use it. When the stored hot water runs out, you wait while the burner or elements catch up. A tankless unit stores almost nothing. It senses flow when a hot tap opens, fires a large burner or heating element, and heats water as it passes through a heat exchanger.
Neither design is automatically better. The right choice depends on how many fixtures run at once in your house, what the gas line and venting can support, how much effort you will put into upkeep, and how long you plan to stay. In Fullerton, where many homes still have the original garage tank location, the existing gas and flue setup often decides how simple a switch will be.
Side by side
General differences between the two designs. Specific models vary, so read the spec sheet for any unit you are considering.
Tank water heater
- Stores a fixed volume of hot water; can run out during heavy use
- Smaller burner that runs longer
- Usually reuses an existing flue and gas line when replaced like for like
- Must be seismically strapped in California
- Sediment collects at the bottom; periodic draining is recommended
Tankless water heater
- Heats on demand; supply depends on flow rate, not stored gallons
- Much larger burner that fires in short bursts
- Often needs a larger gas line, new venting and a nearby outlet
- Wall-mounted per the manufacturer's bracket instructions
- Scale builds in the heat exchanger; flushing on a schedule is important
How Fullerton conditions tip the balance
| Local factor | Effect on a tank | Effect on tankless |
|---|---|---|
| Hard water from blended groundwater and imported supply | Sediment and scale at the bottom of the tank | Scale inside a narrow heat exchanger, which reduces flow and triggers codes if not flushed |
| Garage tank with a roof flue | Straight replacement often reuses it | Usually needs a new vent route sized for the unit |
| Gas line sized decades ago for a tank | Typically adequate for a similar tank | May be too small for the tankless burner at full fire |
| Limited garage space | Tank and strapping take floor area | Wall mounting frees floor space |
Which way are you leaning?
- IfYou often run two showers and a washer at the same timeThenAsk a plumber to size a tankless unit for that combined flow, or compare it with a larger tank.
- IfYour current tank is fine and the gas line is smallThenA like-for-like tank replacement may be simpler when the time comes; get the gas line checked before deciding on tankless.
- IfYou want floor space back in a small garageThenTankless is worth pricing, with venting and gas work included in the quote.
- IfYou do not want to flush anything, everThenBe honest about it. A tankless unit in hard water needs regular flushing to last.
Questions to bring to a plumber
- How many fixtures can this unit serve at once at the temperature we want?
- Is our existing gas line large enough, and how did you check?
- Where will the vent go, and what material does the manufacturer require?
- Will you install service valves so the unit can be flushed?
- What is your CSLB license number?
Common questions
Will a tankless heater give me endless hot water?
It will keep heating as long as demand stays within its flow rating. If too many fixtures run at once, the water may cool or the flow may drop.
Is tankless always more efficient?
It avoids keeping a tank hot all day, but real savings depend on your household's use, the unit, and how well it is maintained in hard water.
Can I put a tankless unit where my old tank was?
Often, yes, but the venting and gas line usually need changes. A plumber should confirm clearances and the vent route for that spot.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.