What Size Tankless Water Heater Do I Need for a 2/3/4 Bathroom House

Read our comprehensive sizing guide here

You just want a quick answer, don’t you? If you’re in a hurry, mind checking out the end of this page (or click here). I’ve put my product recommendations there.

For the rest of you, who really want to understand what size tankless water heater would be the best choice for their house, – keep reading.

In this article, I explain in simple words (and images) how to find the best tankless water heater for your needs and not overpay.

How to read the specifications

First of all, you need to know what are the most important specifications of tankless water heaters. What you should look at when choosing one.

There’s only one most important thing. It’s the flow rate at given temperature rise.

The greater the flow rate, the more hot water a tankless can provide per minute.

To find out what’s your preferred flow rate, you need to determine the peak load for your house and family and find out the temperature rise in your region. Then just choose a tankless accordingly.

An undersized tankless water heater would not be able to provide enough hot water for your needs. An oversized unit is going to cost you a fortune.

We’ve covered the sizing process in our very detailed guide here.

In short, you determine the peak demand by adding up the flow rates of all the fixtures you’re planning to use at the same time.

Most likely, you have no clue how to do it. If that’s the case, use the calculator below. Enter the number of fixtures and you’ll get the total flow rate. Feel free to ask any questions in the comments section, if you still don’t know what to do.

Fixture TypeQuantity
Bathroom Faucets
Bathroom Faucets
Hand Washing Sink
Hand Washing Sink
Bathtub Faucet
Bathtub Faucets
Kitchen Faucet
Kitchen Faucets
Washing Machine
Washing Machine
Total Flow Rate
Total Flow Rate

Now that you know your demand, you need to determine the temperature rise.

The temperature rise is the difference between your set output water temperature and inlet water temperature. Subtract the groundwater temp from the preferred shower temp and you'll get your temperature rise.

The shower temperature is usually about 110-115°F. You can find the groundwater temperature in your region in our map below. Hover over your state (or tap on it from a mobile device) and you'll get the number.

Desired Outlet Temperature (F)
Ground Water Temperature (F)
Required Temperature Rise (F)
enter the groundwater

Great! You know the two most important things you'll need to choose the best tankless water heater for a 2 (or 3, or 4) bathroom house.

Now just go to our main rating and find a model that would fit your requirements.

Keep in mind, that the flow rate you see in the table is the maximum load a tankless can handle in perfect conditions. Use the table for navigation, but make sure that the model you choose can supply enough hot water at your temperature rise.

Best tankless water heater for 2 bathrooms

Again, it all depends on your requirements. My recommendation may not be the right choice in your situation.

But just to give you a starting point for further research, I recommend Rinnai V65iN.

Rinnai V65iN Indoor Gas Tankless Water Heater

Rinnai V65iN Gas Indoor Tankless Water Heater Features and Specifications:
  • UEF (Efficiency Rating): 0.8
  • Product dimensions: 13.9 x 8.8 x 23.6 inches
  • Flow rate: 6.5 GPM
  • Activation Flow Rate: 0.26 GPM
  • Energy Star® certified
Read Verified Customers Reviews

Rinnai V65iN can provide astonishing for its price range 6.5 GPM. It is a perfect tankless water heater for 2 bathroom house. It would best fit for middle-sized homes in states with a warm or moderate climate.

For homes in the northern states, I'd recommend a more powerful model from this series (click the link to check it out).

If the natural gas is not an option in your area and you need an electric unit (although I always prefer gas/lp over electric), I would recommend this one:

EcoSmart ECO 27 Electric Tankless Water Heater

EcoSmart ECO 27 Electric Tankless Water Heater:
  • Max. Flow Rate: 5 GPM
  • Activation Flow Rate: 0.25 GPM
  • Dimensions: 17"H x 17"W x3.75"D
  • Service Requirements: 113 amps (3 double pole x 40 amp breakers)
  • 99.8 Energy efficient
Read Verified Customers Reviews

Best tankless water heater for 3 bathrooms

In a 3 bathroom house, you'd typically want to use at least 2 showers simultaneously. But let's not forget about other appliances like washing machine or dishwasher which may require up to 2 gallons per minute of hot water each.

For this level of demand, you'd want something really powerful. Especially at the times when you need all 3 baths or showers. The peak demand is probably between 7 GPM and 9 GPM.

Considering the great performance and the maximum flow rate of about 9.4 GPM and relatively low price, Rinnai RL94iN - a natural gas tankless water heater is the best choice for 3 bathrooms and additional house appliances.

Rinnai RL Series HE+ Tankless Hot Water Heater

Rinnai RL Series HE+ Tankless Hot Water Heater:
  • Fuel Type: Natural Gas or/and Liquid Propane
  • UEF (Efficiency Rating): 0.81
  • Product dimensions: 14 x 10 x 23 inches
  • Max. Flow rate: 9.4 GPM
  • Energy Star certified (may be available for rebates)
Read Verified Customers Reviews

Don't be fooled by the max. flow rate number. Don't forget that it's the maximum possible score for very warm climates. In real life, it would handle just about what you need. That is between 7GPM and 9GPM, depending on the temperature rise.

It's also not the most efficient model. But considering the price, it's probably the best you can get for your needs. If you're in doubt, check out our reviews of the best tankless water heaters and choose what you think would fit best for you.

Best tankless water heater for 4 Bathrooms

It's not very easy to choose tankless water heaters for large homes. Especially if you live in the north of the USA. The climate is cold, the groundwater temperature is low. The right choice must have a great performance score or it would not be able to handle the heavy load of 4 bathrooms.

In my opinion, your best option here is Rinnai RUR199iN. It's very efficient and one of the most powerful tankless water heaters on the market. It's not cheap though.

Please, recheck twice or even three times if it meets your requirements. Otherwise, you may spend a couple of thousands of bucks for lukewarm showers, since the unit may not be able to heat enough water and handle all the load.

If you live in the south or you don't plan on using all of your four bathrooms at the same time (but still be able to use them whenever you need), Rinnai 199iN would be a 100% fit.

🥇 Rinnai RUR199iN Tankless Water Heater for 4 Bathroom House

Rinnai RUR199iN Features and Specifications:
  • Fuel Type: Natural Gas
  • UEF (Efficiency Rating): 0.93
  • Product dimensions: 22.1 x 14.8 x 33.9 inches
  • Max flow rate: 11 GPM
  • Built-in recirculation pump
Read Verified Customers Reviews

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