The starting point
A family in a 1970s two-story house in north Fullerton wants to replace an aging tank water heater in the garage with a gas tankless unit. The gas meter is on the side of the garage, the furnace is in the attic, and the kitchen has a gas range. A previous owner added a gas fireplace in the family room.
The family assumes the swap is a one-for-one replacement. The first contractor they talk to asks for the tankless unit's spec sheet and a list of the other gas appliances before giving any price.
The appliance list the family put together
| Appliance | Location | Notes |
|---|---|---|
| Furnace | Attic | Original-era unit, recently serviced |
| Range | Kitchen | Replaced a few years ago |
| Gas fireplace | Family room | Added by a previous owner |
| Dryer | Garage | Gas |
| Planned tankless water heater | Garage | Large input at full fire |
How the contractor worked it out
- Total the load.Adding the tankless unit's maximum input to the other appliances showed a large jump from the old tank.
- Check the pipe.The pipe leaving the meter was sized for the original appliances. It could not carry the new total over the run to the attic branch.
- Choose a route.Because the meter and water heater were both on the garage wall, a short dedicated line from the meter outlet to the tankless unit was the simplest fix, leaving the existing piping for the other appliances.
- Flag the meter.Because total demand rose substantially, the family was told to contact SoCalGas about whether the meter could supply it.
- Permit and venting.The contractor pulled the permit and planned venting made for the new unit rather than reusing the tank's vent.
How the project unfolded
- Planning
- Load calculation, route, venting plan and a written scope.
- Before install
- Family contacts SoCalGas about meter capacity; permit is issued.
- Install day
- Old tank removed, new gas line run from the meter, unit mounted and vented.
- Test
- New piping pressure tested; inspection completed as the city required.
- Start-up
- Unit fired, tested at high demand with showers running, and other appliances checked.
What would have changed the plan
- IfThe water heater were far from the meterThenA longer dedicated line, possibly through the attic.
- IfThe meter could not carry the new loadThenWaiting on SoCalGas before the install.
- IfThe family planned a pool heater tooThenSizing for both at once.
Common questions
Is this a real job?
No. It is a composite example written to explain how tankless conversions are often planned.
Would every tankless swap need a new line?
Not always. It depends on the existing pipe size, the run and the other appliances.
What about hard water?
Local water can be hard, so ask about descaling and the maker's maintenance recommendations for a tankless unit.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.