The plan
Illustrative example. Not a real job or customer.
A household adds a primary suite at the far end of a long single-story house. The existing tankless unit sits in the garage at the opposite end. Hot water already takes a while to reach the back bathroom, and the new suite will be even farther.
- The family lists peak demand after the remodel: two showers, a soaking tub and the kitchen.
- A licensed plumber reviews the existing unit's flow rating, gas line and pipe routes.
- The plumber lays out two options in writing.
The family compares the options on comfort, gas supply and how the work fits the remodel.
The two options
One larger unit in the garage
- Replaces the existing unit with a higher flow rating
- Gas line likely needs upsizing for the bigger burner
- Long wait for hot water at the new suite unless recirculation is added
- One unit to flush and maintain
A second unit near the new suite
- Short pipe run, faster hot water at the suite
- Needs its own gas branch, vent route and outlet
- Existing unit keeps serving the rest of the house
- Two units to flush in hard water
What tipped the decision in this example
- IfThe remodel already opened the wall near the suiteThenRunning a gas branch and vent there was simpler than expected.
- IfThe existing unit was still young and healthyThenKeeping it avoided replacing a working heater.
- IfThe family disliked waiting for hot waterThenA unit near the suite solved the wait without a recirculation loop.
Planning lessons
In this invented case, timing mattered. Because walls were open for the remodel, adding a second unit cost less disruption than it would have later. The family also confirmed the total gas load for both units and the existing appliances, and the permit covered the new gas, venting and plumbing together.
Two units do mean two maintenance schedules. The family added both to one flushing log so neither would be forgotten.
Questions for your own remodel
- How far will the new bathroom be from the existing heater?
- Can the gas line support a larger unit, a second unit, or neither without upgrades?
- Is this the right moment to add a recirculation return line while walls are open?
Common questions
Is this a real remodel?
No. It is an invented example written to show the trade-offs.
Is a second unit always better for a far bathroom?
Not always. It depends on gas, venting, cost and how the house is laid out.
Does a second unit need its own permit?
It is often covered with the remodel permit, but check with the City of Fullerton for your project.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.