BUYING GUIDE
What Size Tankless Water Heater Do I Need?
Tankless sizing comes down to simultaneous hot-water flow and required temperature rise. Use both values, then confirm the result against the exact model performance information.
KEY POINTS
What to understand first
Simultaneous demand
Add only the hot-water fixtures likely to run at the same time.
Temperature rise
Subtract realistic incoming-water temperature from the desired outlet temperature.
Operating conditions
A headline GPM value is not a promise at every inlet temperature and setpoint.
Utility capacity
Confirm the home can support the selected fuel, voltage and installation requirements.
PLAIN-LANGUAGE GUIDE
Size for the busiest realistic moment
Begin with a normal high-demand period, such as two showers running while a kitchen faucet is used. Record the actual flow of those fixtures instead of relying on a whole-home fixture count.
Next, calculate the temperature rise. Colder incoming water requires more heating, so the same heater may support less flow in winter or in colder regions. Match both numbers to the exact model chart.
PRACTICAL CHECKLIST
Build your sizing worksheet
Use this list to organize the information needed for a model-specific decision.
List concurrent fixtures
Use the fixtures that may realistically overlap.
Measure or verify flow
Use fixture labels, specifications or a simple measured estimate.
Use a cold-season inlet value
Ask the local utility or installer for a realistic low inlet temperature.
Confirm the performance chart
Check the model at the required flow and rise, not its highest advertised output.
Verify utilities
Confirm gas supply or electrical service before purchase.
Review with an installer
Have a qualified professional confirm the final model and site.
WORKED METHOD
A simple sizing relationship
Required temperature rise = desired outlet temperature − incoming-water temperature.
Then compare that rise and the combined simultaneous flow with the exact model performance data.
CURRENT NOVIEEX EXAMPLES
Use verified product data as the final check
Compare how current models describe output and utilities. These are examples for specification review, not automatic recommendations.
GAS EXAMPLE
NOVIEEX Tankless Gas Water Heater – Propane 5.3GPM
- Outdoor
- Propane
- Up to 5.3 GPM
ELECTRIC EXAMPLE
NOVIEEX 18kW Electric Tankless Water Heater – 240V, Instant Hot Water
- Indoor
- 18kW
COMMON QUESTIONS
Frequently asked questions
Should I add every faucet in the house?
No. Add the fixtures that may realistically use hot water at the same time.
Why does incoming-water temperature matter?
Colder inlet water creates a larger temperature rise, which can reduce available flow.
Is the largest model always safer?
No. Oversizing does not replace utility, installation and model-specific checks.
NEXT STEP
View Current Water Heaters
Continue with the current NOVIEEX product information and model-specific requirements.