Rinnai Tankless Water Heater Sizing Calculator
Use this tool to determine the correct Rinnai tankless water heater model based on your flow rate and temperature needs.
List of the Best Rinnai Tankless Water Heater:
Why Use a Rinnai Tankless Water Heater Sizing Calculator?
Rinnai is one of the world’s leading brands in tankless water heating systems, known for their performance, durability, and innovation. But choosing the right model isn’t just about brand trust — it’s about proper sizing. That’s where our Rinnai tankless water heater sizing calculator comes in. This tool helps homeowners, contractors, and installers determine the best Rinnai tankless water heater model for their home, based on two key factors: hot water demand (GPM) and temperature rise.
How the Rinnai Sizing Calculator Works
The calculator takes three main inputs:
- Total Flow Rate (GPM): Gallons per minute needed during peak hot water usage.
- Incoming Water Temperature: Groundwater temperature, which varies by region.
- Desired Output Temperature: Usually set between 115–125°F for comfort and hygiene.
Using this information, the calculator estimates the required heating power and compares it to Rinnai models to suggest a match.
Why Sizing Accuracy Matters for Rinnai Tankless Heaters
If your unit is too small, you’ll run out of hot water during peak times. If it’s too large, you may overspend on the unit itself, as well as operating and installation costs. Rinnai heaters are high-efficiency systems, but only when properly sized to your household’s water usage patterns.
Rinnai Tankless Models Overview
| Model | Max GPM | Temp Rise at Max GPM | Fuel | Application |
|---|---|---|---|---|
| V65iN | 6.5 | 35°F | Natural Gas | Small homes, 1-2 bathrooms |
| V75iN | 7.5 | 35°F | Natural Gas | 2-3 bathrooms |
| RL94iN | 9.4 | 35°F | Natural Gas | 3-4 bathrooms |
| RU160iN | 7.0 | 60°F | Natural Gas | Cold climates, higher rise |
| RU199iN | 9.8 | 60°F | Natural Gas | Whole house, multiple showers |
Common Fixture Flow Rates
Estimate your household’s peak GPM using these average fixture values:
- Shower: 2.0–2.5 GPM
- Bathroom faucet: 0.5–1.0 GPM
- Kitchen sink: 1.0–2.2 GPM
- Dishwasher: 1.5–2.0 GPM
- Washing machine: 2.0–2.5 GPM
Example Usage Scenarios
If you’re running two showers and a kitchen sink simultaneously, that’s a demand of around 6.5–7.5 GPM. If your incoming water is 50°F and you want 120°F output, your required rise is 70°F. In this case, only Rinnai’s high-output models like the RU199iN would be appropriate.
Climate and Temperature Rise
Temperature rise is crucial. In warmer climates like Florida or Southern California, groundwater might enter at 65°F, meaning less rise and smaller unit needed. But in northern states like Minnesota or Maine, groundwater can dip to 35–40°F, requiring much more power to reach usable temperatures. The calculator automatically takes this into account.
Installation and Efficiency Tips
- Always install your Rinnai heater as close as possible to the point of use to minimize delay.
- Consider Rinnai recirculation systems to avoid cold water “sandwiches.”
- Use a water softener if you live in a hard water area to prolong heater life.
- Install low-flow fixtures to reduce peak GPM demand.
- Have your system professionally installed and inspected.
FAQs About Rinnai Tankless Water Heater Sizing
Can I install a Rinnai tankless heater outdoors?
Yes, Rinnai offers indoor and outdoor models. Make sure you select the correct variant for your climate zone and installation site.
Is it safe to oversize a Rinnai water heater?
Moderate oversizing is okay, but it can lead to reduced efficiency and higher costs. Proper sizing is always recommended for best performance.
Can I connect two Rinnai units in parallel?
Absolutely. Rinnai offers systems and accessories to link multiple heaters for high-demand applications like large households or commercial settings.
What maintenance do Rinnai units require?
Flush your heater annually to remove scale buildup, especially in hard water regions. Rinnai heaters are low-maintenance but benefit from routine inspection.
Final Thoughts
Using our Rinnai tankless water heater sizing calculator is the best way to eliminate guesswork and ensure long-term satisfaction. Whether you're replacing an old water heater, upgrading for energy efficiency, or installing a new system in a cold climate, correct sizing is the key to reliability, performance, and comfort. Rinnai’s wide range of models means there’s always a perfect fit — and our calculator helps you find it with confidence.