Why gas sizing matters more for tankless
A tank heater warms water slowly over time, so its burner is modest. A tankless heater has to raise cold water to shower temperature in the few seconds it takes to pass through, so its burner draws far more gas while it is firing. If the pipe from the meter is too small or too long for that demand, the unit can starve for gas when the furnace, range or dryer is running too.
Starved units tend to show ignition or flame codes, deliver lukewarm water at high flow, or work fine alone and fail when other appliances run. The fix is in the piping, not the heater, which is why gas sizing should be checked before any tankless install or when these symptoms appear.
Terms you will hear
- Gas line sizing
- Matching pipe diameter and length to the total gas demand of every appliance on that line.
- Meter
- The utility's gas meter outside the house. SoCalGas owns and services the meter; piping after it belongs to the home.
- Sediment trap
- A short capped leg at the appliance connection that catches debris before it reaches the gas valve.
- Vent termination
- Where the exhaust pipe leaves the house through a wall or roof.
- Condensate
- Acidic water produced by high-efficiency units, which needs a proper drain route.
Signs the gas or vent may be the problem
How a plumber usually checks it
List the gas load
Add up the input ratings of every gas appliance on the system.
Measure the run
Trace pipe size and length from the meter to the heater.
Test under load
Check gas pressure at the heater with other appliances running.
Inspect venting
Confirm the vent material, length, slope and termination clearances match the manufacturer's instructions.
Explain findings in writing
Describe what is undersized or incorrect and what would correct it.
What affects cost
- Pipe route
- Distance from the meter and how many walls or floors the line passes.
- Meter capacity
- If more total gas is needed, SoCalGas may need to be involved; ask the plumber to coordinate.
- Vent changes
- Rerouting or replacing vent pipe can involve exterior walls.
- Permits
- Gas piping work commonly needs a permit; check with the City of Fullerton.
Questions to ask
- Is my gas piping sized for every appliance running at once, including this heater?
- Did you test gas pressure at the heater with other appliances on?
- Does the venting match the manufacturer's installation instructions?
- Will this work need a permit and inspection?
- Do I need to contact SoCalGas about the meter?
Common questions
Can I check the gas line myself?
You can note symptoms and look at the vent from outside. Gas piping should only be opened, changed or tested by a licensed plumber.
Who handles the gas meter?
SoCalGas services the meter. Piping on the house side of the meter is the homeowner's responsibility.
Is a carbon monoxide alarm a good idea near a gas heater?
Yes. California generally requires CO alarms in homes with fuel-burning appliances; check that yours are installed and working.
General information for Amerige Heights, not a quote or professional advice. In an emergency, call 911.