How Big Of Tankless Water Heater Do I Need
Written by: Gene Fitzgerald // Last Updated:
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Tankless water heaters provide endless hot water on demand. Furthermore, they can reduce your utility bills by more than than 30 percent due to the emptying of standby energy losses, they are about the size of a suitcase and therefore space-saving, and they last up to xx+ years which is near twice as long as what you exit of a regular tank-based unit.
However, tankless h2o heaters are limited by how much water they tin heat at any given fourth dimension. Choose too small of a organization and information technology won't have the capacity to provide plenty hot water to encounter your household needs. Get too big and you lot volition overpay. This is why proper sizing is cardinal – before making a purchase.
This buying guide volition walk you through the process of sizing a tankless water heater and likewise shed light on other aspects that you lot take to consider when shopping.
Contents
- How to size a tankless h2o heater
- Step 1: Menses rate – how many gpm for a tankless water heater
- Stride 2: Temperature rise
- Step 3: Putting it all together
- Video
- Size nautical chart
- Example size chart
- Tankless water heater sizing calculator
- Frequently asked questions
How to Size a Tankless Water Heater
Simply put, tankless a.chiliad.a. on-demand water heaters are rated by their maximum output water flow charge per unit at a specific temperature rise.
So, in club to size a tankless h2o heater you have to consider 2 things:
- How many gpm (gallons per minute) of hot h2o you need at times of peak consumption. Remember, tankless water heaters don't store any h2o just heat it every bit it flows.
- The required temperature ascension which is determined by feed water temperature and output water temp settings.
What if you undersize?
Bad idea! If the required hot water demand surpasses the possible maximum, even if just temporary, almost water heaters volition throttle the flow automatically. This ways less hot water at every outlet and therefore a temperature and/or pressure level drop.
In addition, a tankless water heater that runs at full speed all the time is more likely to break down prematurely.
What if you lot get too big?
Oversizing is not that big of a deal. The only issue is unnecessary upfront toll.
Stride 1: Flow Rate – How Many GPM for a Tankless H2o Heater
Permit'southward start by figuring out your peak hot h2o need. You can use the chart below for this. It lists the standard flow rates of different types of water outlets sold in the U.S. Of form, yous could also expect up your specific fixtures etc. online or check their product manuals.
Just determine which devices yous want to exist able to run simultaneously and how many of them. And then add upwards their flow rates.
For case, if yous need i shower and 1 kitchen faucet running at the same time your required maximum water menstruum is:
2.5 gpm + two.ii gpm = 4.vii gpm
For WaterSense-certified products, the required flow rate is:
two.0 gpm + i.5 gpm = 3.v gpm
Pretty simple! But earlier yous get started, here are a few more tips:
- By planning for maximum demand at peak hours like in the morning you tin can ensure that yous ever accept hot water at the ready no affair what. Above that, a tankless water heater that does non have to run at full capacity all the time is likely to terminal longer. At the same time, a piffling planning will allow you to reduce your top need significantly. This includes taking turns when showering, letting the dishwasher do its thing while everyone is out of the house, and preparing your nutrient earlier or afterwards the showers are finished.
- Obviously, you have to accept into business relationship not but the number of bathrooms in your home, but also how many people are living under 1 roof. 2 people tin only utilise two showers at the same time, even in a v-bath mansion.
- Ask yourself: Will the water heater serve your entire abode or just parts of it?
- The menstruum rates listed below indicate total water output, so hot h2o PLUS cold water. In other words, showering with a ii.5 gpm shower caput does non mean that all of the water will be hot. It is more likely that you mix in some common cold to get the desired temperature. Thus, the actual hot water demand is somewhat lower.
- To reduce flow rates you could install low-flow aerators or fixtures.
| Water Outlet | Standard Period Rate |
|---|---|
| Manus washing sink | 0.5 – 1.5 gpm |
| Shower caput | 2.five (2.0*) gpm |
| Bathroom faucet | two.2 (1.5*) gpm |
| Bathtub faucet | 3.0 – 4.0 gpm |
| Kitchen faucet | 2.2 gpm |
| Washing machine | 23+ gallons per load, gpm hard to determine |
| Dishwasher | 6 gallons per load, gpm hard to determine |
*WaterSense certified products
Please note: Older fixtures are likely to have higher flow rates.
As you lot can see, nosotros did not include flow rates for washing machines and dishwashers. This is because we establish information technology very difficult to get reliable data on this. Some sources say ii to iii gpm, others i.5.
What you could do is run each apparatus separately and monitor your h2o meter and measure out time. This will give you lot a rough idea of how much menstruum is needed.
Speaking of measuring, for a more scientific approach to determining your acme water flow you tin can take a one-gallon bucket and track how long it takes your shower head, kitchen faucet, bathroom taps, etc. to make full it. Then use the following formula to calculate the flow rate for each outlet:
Flow rate = sixty / Seconds required to fill up bucket
If you don't want to waste product a total gallon per outlet, only fill up a quart and employ this formula instead:
Catamenia rate = 15 / Seconds required to make full ¼ bucket
Pace 2: Temperature Ascent
The adjacent step is to determine your required temperature rise. Hither all you have to practise is subtract the temperature of your feed water from the desired output h2o temp.
Required temp ascent = Output water temp – Feed water temp
How tin you detect out what temperature your feed h2o has? You take two options:
- Measure with a thermometer
- Use our awesome U.S. average groundwater temperature map
Delight note: These are average temperature estimates. Real temperatures vary with flavour and weather.
As you can see, where you live in the country plays a huge role as far as average groundwater temperature is concerned. In warmer climates in the south, the temperature will naturally be college, up to 77 °F in southern Florida. Whereas in Alaska, parts of Due north Dakota, Minnesota, Wisconsin and other states in far northern regions the groundwater temp tin be every bit low as 37 °F.
At present, this makes a big departure as to how much a tankless water heater has to work to bring water up to the desired temperature. Let's say you live in Michigan with twoscore °F average feed h2o temperature. And y'all aim at 110 °F output temp. The required temperature rise would be
110 °F – forty °F = 70 °F
A water heater installed in a abode in Texas with 70 °F inlet h2o temp has to warm upwards the h2o by as little as
110 °F – 70 °F = twoscore °F
Past the way, 105 to 115 °F output water temp is considered ideal for everyday household use. 105 °F is considered the upper end of the temperature range most comfy for showering. At your kitchen sink you lot desire something around 110 °F.
Step 3: Putting It All Together
Okay, y'all know your hot h2o demand at tiptop hours as well as the required temperature ascent.
The final pace is to leave and look for a tankless water heater that meets these requirements. Basically all manufacturers provide sizing charts with their products that specify maximum menstruum rates at a given temperature ascension or vice versa. Some manufactures also list menses rates for different input/output h2o temps.
You want to cull a unit size that either meets or exceeds your tiptop hot water demand.
Be aware, though, that manufacturers like to promote their products using all-time-case scenarios, and then have the information with a grain of salt. Some companies tend to exaggerate with what their systems can do…
Ready for the next pace? Bank check our electrical tankless water heater reviews to find a system that perfectly fits your needs!
Video
Prefer video? Bank check this out:
Size Chart
Check out a few size charts and you will quickly notice that gas or electric makes a huge difference. Generally speaking, tankless gas water heaters are more powerful, meaning that they tin produce higher gpm than electric units at the same temperature rising.
For example:
If your required temperature rise is 70 °F, a large tankless gas water heater can supply 5.0 – 5.v gallons per minute. The largest electric unit (36 kW) maxes out at footling more than than 3.0 gpm.
Example Size Chart
For reference, this is what a tankless h2o heater sizing chart looks like:
This particular heater can provide 6.vi gpm at a 50 °F temperature rise and 4.8 gpm at 70 °F.
Popular Tankless Water Heaters
These are some real-life examples of popular tankless water heaters:
(Mobile Hint: Swipe to Scroll)
| Model | Fuel Type, Power | Temp Rise | Max GPM | # of Bathrooms |
|---|---|---|---|---|
| Rinnai V75iN | Natural gas, 180,000 BTU | 70 °F | 4.iii gpm | 1 – 2 bathrooms |
| fifty °F | 6.0 gpm | two – 3 bathrooms | ||
| Rinnai RU199iP | Propane, 199,000 BTU | 70 °F | 5.five gpm | ii bathrooms |
| 50 °F | 7.half dozen gpm | iii bathrooms | ||
| Stiebel Eltron Tempra 36 Plus | Electric, 36 kW | 70 °F | iii.5 gpm | 1 bathroom |
| fifty °F | 4.75 gpm | 1 – 2 bathrooms | ||
| Rheem RTEX-18 | Electric, xviii kW | 65 °F | 2.0 gpm | i bathroom |
| 55 °F | 2.0 gpm | 1 bathroom | ||
| EcoSmart ECO 11 | Electric, 11 kW | 68 °F | ane.1 gpm | 1 bathroom |
| 48 °F | 1.56 gpm | one bathroom |
Frequently Asked Questions (FAQ)
1. What Size Tankless Water Heater Do I Need for a Family of 5?
This is almost impossible to tell. It depends on how many bathrooms and water using appliances you accept, and the required temperature rise. Become through steps one to iii in this sizing guide or use our tankless h2o heater sizing estimator and yous volition get an answer to your question – guaranteed!
ii. What Size Tankless H2o Heater Do I Need to Replace a 50-Gallon H2o Heater?
Once again, this is simply non enough data to give a reliable answer. Information technology depends on how many bathrooms and h2o using appliances y'all have, and the required temperature rise. We recommend you go through steps one to 3 in this sizing guide or employ our sizing calculator!
3. How Many Tankless Water Heaters Exercise You Need?
How many tankless water heaters you need depends on your peak hot water demand and required temperature rise (bank check sizing guide above).
In general, one tankless gas water heater should be enough to supply a mid-sized family/abode. Electric tankless water heaters are perfect for smaller families and apartments.
In case of very high demand, consider installing ii or more than heaters, either at the point of employ and so they work separately from one another or in ane key spot to work in tandem operating equally a unmarried unit.
Furthermore, although more expensive upfront, adding ii smaller units in serial can sometimes brand more sense than installing i large one.
If you lot have whatever thoughts or questions almost how to size a tankless water heater please don't hesitate to leave a comment below!
How Big Of Tankless Water Heater Do I Need,
Source: https://www.best-osmosis-systems.com/tankless-water-heater-sizing/
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