Before you go to our list of the best tankless water heaters on the market, you need to know EXACTLY what size tankless water heater you would need for your home. Show
And here’s why: If you choose a too small tankless water heater, you may end up taking cold showers when somebody else in the house is using hot water. But if you buy a too big tankless water heater, it won’t come cheap. You’ll overpay for what you probably will never use. So you may wonder, how do I know how big of a tankless water heater would I need? The answer is in this article! I’ll explain how to choose the right size of a tankless water heater in 3 easy steps, so you don’t overpay for excessive performance. You’ll learn how to properly size a tankless water heater for your home. Use our tankless water heater sizing guide and tables and tankless calculator to figure out what exactly you need. So, here’s how you do it: 1 Calculate the combined flow rate (in GPM)How many gallons per minute (GPM) do I need for a tankless water heater? Go to step 1 2 Determine the temperature rise in your regionUse our groundwater temperature map to determine the temperature rise in your region Go to step 2 3 Put it all togetherPick the brand and the model that meets all the requirements Go to step 3 Before getting into the details, consider checking out this water heater as one of the best “fit-for-all” models. Sale
 Rinnai V65iN Non-Condensing Natural Gas Tankless Water Heater, Indoor Installation, Up to 6.5 GPM
Or this electric alternative: Sale
Ecosmart ECO Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology, White
Now to the useful stuff: Step 1: Determine the combined flow rate (in GPM).With traditional storage water heaters, you could calculate the size of it based on the number of family members and how much water each of them uses. Whereas with tankless water heaters, it’s more important to know how many fixtures it’s required to serve simultaneously. It doesn’t matter how much people are going to take showers if they use it one by one. With tankless water heaters, you’ll have an endless supply of hot water. However, if several people are going to use two or more showers at the same time, an undersized tankless water heater may not be able to handle the demand. That’s why you’ll need to calculate how many gallons of hot water per minute must be heated to supply the peak demand. Although it may sound too “professional,” it’s very easy to do:
If you don’t know the actual flow rates for your shower or faucets, you can use our table of the average flow rates for most types of fixtures:
Or you could apply a scientific method and measure the flow rate by yourself. Take a 1-gallon bucket, open the fixture (showerhead, faucet, bathroom taps, etc.), and measure how long it will take to fill the bucket. Then apply this formula: Flow rate = 60 / seconds a fixture took to fill the bucket If you don’t want to waste several gallons while doing the test measure, fill in a quarter of the bucket and apply this formula: Flow rate = 15 / seconds a fixture took to fill a quarter of the bucket Now let’s see how you determine the total required flow rate by looking at the following example: Let’s say you have two bathrooms. And you want to be able to use both of them simultaneously. Plus a kitchen sink and a washing machine will be used too. If we take the table above as a reference, we’re going to end up with this equation: So if you want to use all the fixtures and appliances at the same time, your tankless unit should be able to provide 8+ GPM of hot water. Keep in mind that you should only count the fixtures and appliances that you want to run simultaneously. Don’t count them just for the fact that you have them. You could have noticed that we took the maximum possible flow rate number from the chart, which is rarely true in real life. But it’s always better to overestimate a little than underestimate. Just to be safe. Now you can decide whether you want to buy one big whole house tankless water heater (like Rinnai RUC98iN) or use a smaller one (like this) and buy additional smaller units for bathroom, shower, or appliances. The decision may depend on one factor: the length of the pipes. The further your fixtures are from the tankless water heater, the longer you’ll have to wait before the hot water gets to the fixture. A small point of use tankless water heaters solves this problem by boosting up the water temperature right where they’re used. Use low flow showerheads to reduce the total flow rate and save money! If you use low-flow showerheads, your hot water demand is going to be lower, and you won’t need a huge and expensive tankless water heater. Modern low-flow showerheads provide the same water pressure and give you the same shower experience as higher-flow models. But there’s also a downside to these showerheads. If the flow rate is too low, the tankless water heater may not be activated since they have different activation flow rates. That’s something to keep in mind when choosing one for yourself. The lower the activation flow rate, the better. Step 2: Determine the temperature rise in your regionNow that you calculated how much water you need to heat per minute, you should determine how hot the water should be. In other words, you have to determine the temperature rise. Temperature rise is the difference between the temperature of the incoming cold water and the outgoing hot water It’s very important to know since the ACTUAL flow rate of a specific tankless water heater largely depends on the temperature rise. You can’t get an 11 GPM flow rate with Rinnai RUR199iN in Boston in winter. But you surely can in Miami. So just in case, you didn’t know this, the flow rate that manufacturers put in the description of tankless water heaters is the maximum possible flow rate for that particular model. The number is only true for warmer climates with a very small temperature rise (where the groundwater is warmer). So if you live in the northern states where the groundwater is colder, you’re going to get a couple of gallons of hot water per minute less with the same tankless water heater. The groundwater temp varies in different states throughout the USA. Using our groundwater temperature map, you can easily determine the temperature rise. Just hover over the map to see the groundwater temperature for your region. Desired Outlet Temperature (F) Ground Water Temperature (F) Required Temperature Rise (F) enter the groundwater If you’re still confused, do this:
For example, if you live somewhere in Kansas, your average incoming cold water temperature is about 52°F. So to get 110°F hot water in your shower, you’ll have to heat the water by 110 – 52 = 58°F. So the temperature rise for your region is 58°F. You can use the calculator. Now that you’ve calculated the temperature rise for your region, you’re ready to go to the next step: Step 2.5: Consider peak time usageThis section should have been a part of step 1 as it’s about the flow rate. It’s just a quick reminder. So if you haven’t considered the peak time usage on step 1, please go back and recalculate the number. So what’s it all about? The main point is that when you’re calculating the flow rate when trying to size your tankless water heater, you should consider the peak load and not the average demand. I hope I made it clear. You don’t want to end up getting a cold shower in the busy hours because your tankless couldn’t keep up. You should be prepared for the worst. It wouldn’t hurt much to overestimate your average hot water demand a little bit. Step 3: Put it all together.Ok, at this point, you know your hot water demand and the required temperature rise. Your next move is to go and choose a tankless water heater that meets the requirements. Let’s say you want to find the best tankless water heater to heat the water for a shower, a kitchen sink, and a washing machine all at the same time. And you live in South Carolina. How big of a tankless water heater do I need? The answer is simple: you’ll need a tankless water heater that can provide a temperature rise of 50°F for about 6 gallons of water per minute. The best gas option, in this case, would probably be Rinnai V-series. Remember, the maximum flow rate that manufacturers mention in the description is not what you’ll get at your place. The lower the incoming water temperature, the lower the flow rate a tankless unit would be able to provide. Keep in mind that it’s always better to oversize the unit than buy the one that can’t supply enough hot water. You can check the actual flow rate for your temperature rise in the specifications of a model or in the review section on our round up page. Also, feel free to ask anything in the comments. Our experts will try to help you with sizing if you provide maximum information. Sizing Guide For Tankless Water Heaters: Equivalents Table
This is a rough estimation of how big of a tankless water heater you would need for your situation But there’s more to the sizing process than just a table. You would need to calculate the demand and the temperature rise in your state to properly size a tankless water heater. Tankless water heater sizing calculatorWe thought it would be easier for you to calculate the flow rate and the temperature rise if you could have a simple calculator. So here’s how you can d etermine GPM for a tankless water heater. Just select the number of fixtures and appliances that you are going to use simultaneously, and we’ll calculate the total GPM (based on average numbers). What size tankless water heater do I need to replace a 50-gallon water heater?If you're looking to replace your old tank 50-gallon water heater, you would need a good tankless equivalent for it. So here it is: Sale
Rinnai RL75iN Natural Gas Tankless Hot Water Heater, 7.5 GPM
But before you go and buy it, you need to learn something: You can't size a tankless water heater by the standards of the storage water heater. They don't work that way. With a tankless, you can have endless hot water, so it doesn't matter how big your storage was. If you want to upgrade your water heater size from 40- or 50-gallon storage water heater or replace it, you won't necessarily need a big tankless water heater. The right size is a tankless water heater that can heat enough gallons of water to a specific temperature per minute to keep up with the demand. It's the flow rate and the temperature rise that matter. Now that may sound confusing or/and complicated. Let me put it simply: the size totally depends on the flow rate and the temperature rise. Count all the hot water fixtures in your house that you want to run simultaneously.That's pretty easy to do. Remember that it doesn't matter how many bathrooms your house has. What matters is how many of them you're going to use at the same time. Add up their flow rates.The flow rate is the amount of water that goes through the fixture per minute in gallons. If you don't know the exact numbers, run a test.
FLOW RATE = 15 / Seconds to fill a quarter of the bucket Determine the temperature rise for your region.To determine the temperature rise subtract your groundwater temperature from the temperature you want to have in the shower. For details, refer to our guide here. Pick the right model that meets the requirements.It's not an easy thing to do. With so many trusted brands and models on the market, you can easily get confused. Knowing what requirements it should meet helps to narrow down the list to several brands and models for different power sources and various budgets, of course. We've tried and come up with a list of the best models for most use cases. But if none fits your situation, let us know in the comments please. A sizing exampleFor example, you live in Texas. You want to be able to run two showers plus let a washing machine do its job. And all of this should be running at the same time. Now, let's do the math. The flow rate of an average showerhead is 2-2.5 GPM (gallons per minute). Two of them would be 4-5 GPM. A washing machine consumes about 2 GPM on average. The groundwater temp in your region is between 60°F and 67°F. That results in a temperature rise of about 110°F - 60°F = 50 °F. Now go to our list of the best tankless water heaters and see which one fits your needs best. It should be able to provide 6 to 7.5 gallons of hot water per minute at a temperature rise of 50°F. What size tankless water heater do I need to replace an 80-gallon water heater?Again, if you want to choose the right tankless water heater to replace an 80-gallon tank water heater, you would need to determine the GPM and temperature rise first. If you have a large house and you want to buy a big whole house tankless water heater, go for Rinnai RUR199. It's probably the most powerful tankless water heater on the market. And it's able to supply a large three bathroom house even if you are planning to use them all at the same time plus a washing machine. If this model is too expensive for you, Rinnai RUR160 is the equivalent of an 80-gallon tank water heater (there are both natural gas and propane options). It's cheaper and still very powerful. And if that unit also doesn't fit into your budget, give a look at the Takagi model that's capable of providing up to 10 gallons of hot water per minute. It's much cheaper, but it also works worse than Rinnai in cold climates. And it's old. What Size Tankless Water Heater Do I Need For A Family Of 2, 3, 4, 5
As we've mentioned earlier, with tankless water heaters, it doesn't really matter how many people are there in your house. What matters more is how many of them are going to use hot water at the same time. Let's talk about this in detail. What's the difference?First of all, you need to understand the difference in sizing methods between tank water heaters and tankless water heaters. With old storage water heaters, your showers and hot water usage were limited to the amount of preheated water in the tank. Tankless water heaters provide endless hot water on demand. And I literally mean it. Once the hot water reaches the fixture, you and your family don't have to worry that it's ever going to run out. It's heated on the go. So as long as you have electricity on and the groundwater keeps flowing in, your hot water is going to be there. But as great as it sounds, there are some limits to tankless water heaters. Their performance totally depends on the amount of heat they can provide to heat the water on the go. In other words, the more BTUs, the better. But two similar tankless water heater models may have the same BTU, although one of them may be more efficient than the other. That's why it's more convenient for a consumer to look at the flow rate at the given temperature rise. It shows how much hot water it can supply per minute. And the temperature rise is defined by the difference between the output water temp and groundwater temp. Sounds way too complicated, isn't it? Let me make it easier for you. How big of a tankless water heater do I need?We've already covered most of the necessary info earlier. If you have time, we recommend reading the whole guide. If you don't, I'll try to explain everything really short. So, to determine the right size of a tankless water heater for a family of 5, you'll need to calculate the peak flow rate in your house. And find a tankless model that would be able to handle the load at the needed temperature rise. Let me show how to do it with an example: Let's say you live in California or Texas. With a big family of yours, you'll probably want to be able to use two or three showers simultaneously. Also, you'll want to leave some additional capacity for unpredictable situations. Like using a washing machine or a kitchen sink. The average flow rate for showerheads is 2 GPM. The total flow rate is: (2-3 showerheads * 2 GPM) + 2 GPM for washing machine or a faucet = 6-8 GPM And the groundwater temp in your region is somewhere between 57°F and 67°F. So the temperature rise will be 110-57/67= 53°F to 43°F. Now let's get back to the original question about sizing a tankless water heater. A family of 5 people will require at least a 6 GPM tankless water heater. Here are our recommendations for the best tankless water heaters: In my opinion, the best gas option would be this: If you're looking for electric tankless water heaters options, consider this one: But REMEMBER: electric tankless water heaters almost always will be more expensive in the long run. They usually require serious electric service upgrades and cost more than gas tankless water heaters. So, if gas or liquid propane are available options, I'd go for them. What Size Tankless Water Heater Do I Need For A 2, 3, 4 Bathroom HouseYou just want a quick answer, don't you? If you're in a hurry, check out the start of this article. 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 your house, - keep reading. Below I will explain in simple words (and images) how to find the best tankless water heater for your needs and not overpay. How to read the specificationsFirst 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 a 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 one 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 guide earlier. Mind checking it out? 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. 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 on the map that we presented earlier. Alternatively, just check out the numbers. 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. Example. Let's say you have a one-bathroom house, where you'd want to run one shower and one other appliance at a time. So, if you have a one-bathroom house, you will need a tankless water heater that can heat at least 3 gallons of hot water per minute. We recommend Rinnai or Ecosmart. Best Tankless Water Heater For 2 Bathroom HouseAgain, 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, if you have a two-bathroom house (or two-bedroom house) and you want to run two showers simultaneously, you will need a tankless water heater that can provide at least 5 gallons of hot water per minute. I recommend Rinnai V65iN: Rinnai V65iN Indoor Gas Tankless Water HeaterSale
Rinnai V65iN Non-Condensing Natural Gas Tankless Water Heater, Indoor Installation, Up to 6.5 GPM
Rinnai V65iN can provide astonishing for its price range of 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 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 HeaterSale
Ecosmart ECO Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology, White
Best Tankless Water Heater for 3 Bathroom HouseIn a three-bathroom house, you'd typically use at least two showers simultaneously. But let's not forget about other appliances like washing machines or dishwashers, 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 three 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 HeaterSale
Rinnai RL94iN Non-Condensing Natural Gas Tankless Water Heater, Indoor Installation, Up to 9.8 GPM
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 BathroomsIt'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 Condensing Tankless Hot Water Heater, 11 GPM, Natural Gas, Indoor Installation
Got any questions? Ask them below! Can I replace my 40 gallon water heater with a tankless water heater?Yes. The initial cost of converting your tank water heater to a tankless is expensive. Tankless water heaters are 3x more expensive than your average tank water heater. However, the energy savings and supply of endless hot water can outweigh the cost for many.
How do I choose the right size tankless water heater?The best sizing factor for a tankless water heater is its flow per minute rate. A 3.2 gpm, tankless heater can heat 3.2 gallons of water per minute, which is roughly enough to provide hot water to a shower and a sink. To find the correct capacity, add up all of the fixtures that you expect to use at the same time.
What size tankless water heater do I need to replace a 50 gallon?To replace a 50-gallon water heater, you would, roughly speaking, need: 10 GPM gas tankless heater or at least a 27 kW electric tankless water heater if you live in the northern part of the USA. 7 GPM gas tankless heater or at least an 18 kW electric tankless water heater if you live in the southern part of the USA.
Should I oversize tankless water heater?When it comes to tankless water heaters, size matters. If you install a unit that's too small, you won't have enough hot water to meet demand. On the other hand, an oversized unit will cost more to purchase and operate than necessary, negating one of the biggest benefits of tankless water heaters—energy efficiency!
|
What size tankless water heater to replace a 40 gallon
Related Posts
Copyright © 2024 themosti Inc.
