Rinnai Tankless Water Heater Sizing Calculator
Find the ideal Rinnai tankless water heater based on your hot water needs, number of fixtures, and climate zone.
List of the Best Rinnai Tankless Water Heater:
Rinnai Tankless Water Heater Sizing Calculator: Find the Perfect Fit
This Rinnai tankless water heater sizing calculator helps you quickly determine the best Rinnai model for your household needs. Rinnai offers some of the most advanced and efficient tankless water heaters on the market. With the right model, you'll enjoy endless hot water, energy savings, and precise performance. This guide walks you through flow rate, temperature rise, and how to use this calculator to get an instant recommendation.
Why Choose Rinnai Tankless Water Heaters?
Rinnai is a global leader in residential water heating solutions. Their tankless water heaters are known for advanced technology, reliability, and energy efficiency. Whether you choose a compact unit for a small home or a powerful system for a large family, Rinnai models deliver consistent performance and flexible installation options.
How Does This Sizing Calculator Work?
Our Rinnai tankless water heater sizing calculator uses a simple formula based on:
- Number of bathrooms — Estimating base GPM demand
- Number of simultaneous fixtures — Sinks, showers, dishwashers, etc.
- Incoming cold water temperature — Affects temperature rise
- Desired hot water temperature — Usually set to 120°F
The calculator estimates total gallons per minute (GPM) needed and calculates the required temperature rise. It then recommends the most suitable Rinnai tankless unit.
Understanding Flow Rate (GPM)
Flow rate, measured in gallons per minute, reflects how much hot water your household needs at once. Here are average GPM values for common fixtures:
| Fixture | Average Flow Rate (GPM) |
|---|---|
| Shower | 2.0–2.5 |
| Bathtub | 4.0 |
| Bathroom Sink | 0.5–1.0 |
| Kitchen Sink | 1.0–1.5 |
| Dishwasher | 1.5 |
| Washing Machine | 2.0–2.5 |
For example, if two showers and a washing machine are running at once, you’ll need at least 7 GPM capacity.
What is Temperature Rise?
Temperature rise is the difference between your incoming cold water temperature and the desired hot water output temperature. In most homes, 120°F is ideal. If your local water comes in at 50°F, you need a 70°F rise.
Incoming Water Temperatures by Region (U.S.)
- North: 40–50°F
- Midwest: 45–55°F
- South: 60–70°F
Recommended Rinnai Tankless Models by Capacity
| Model | Flow Rate | Recommended Use |
|---|---|---|
| Rinnai V65iN | 6.5 GPM | 1-2 Bathrooms |
| Rinnai RL75iN | 7.5 GPM | 2 Bathrooms |
| Rinnai RU80iN | 8.0 GPM | 2-3 Bathrooms |
| Rinnai RL94iN | 9.4 GPM | 3 Bathrooms |
| Rinnai RU199iN | 11.0 GPM | Whole-home / Large homes |
Installation Considerations
Rinnai units come in both indoor and outdoor models, as well as condensing and non-condensing types. Keep the following in mind when selecting and installing your unit:
- Indoor units require proper venting (direct vent or concentric vent kits)
- Condensing models offer higher energy efficiency but require condensation drainage
- Ensure your gas line supports required BTUs for your selected model
- Outdoor models must be protected from freezing temperatures
FAQs: Rinnai Tankless Water Heater Sizing
What size Rinnai tankless water heater do I need for a 3-bathroom home?
For 3 bathrooms, the Rinnai RL94iN or RU199iN (9.4–11 GPM) is recommended to ensure you can run multiple showers and appliances at once.
Do Rinnai tankless water heaters work in cold climates?
Yes. Rinnai models are tested to handle temperature rises of up to 80°F and include freeze protection features. Just make sure to select a unit with sufficient GPM at your required rise.
How does the calculator help avoid under-sizing?
By accounting for simultaneous fixture use and temperature rise, this tool avoids low-flow conditions, cold water surges, and underperformance—common issues when units are undersized.
Can I use multiple Rinnai units?
Absolutely. Rinnai's Circ-Logic and EZConnect features support multiple units in parallel, perfect for large homes or commercial properties.
What is the difference between Rinnai V, RL, and RU series?
- V Series: Affordable and compact, good for small homes.
- RL Series: Mid-tier, higher flow and Wi-Fi ready.
- RU Series: High-end condensing, ultra-efficient and ENERGY STAR® rated.
Conclusion: Use This Rinnai Sizing Tool with Confidence
Choosing the right Rinnai tankless water heater ensures you get continuous, reliable hot water for your entire household. Our Rinnai tankless water heater sizing calculator simplifies this process by delivering instant model recommendations based on real-world use cases. Bookmark this page and use it anytime you or your customers need professional-level water heater sizing made easy.