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Your Guide to Home Heating and Cooling Systems

15 Best Tankless Water Heaters of 2022 - Complete Buying Guide

Last Updated on March 28, 2022

Over the course of this article, I’ll go over WHY, correctly, this is the best (starting with how these water heater works, and then what to look for in a tankless water heater) so you’ll feel more informed as to where recommendations come from.

So How Does It Work, Anyway?

It’s pretty darn simple. All tankless water heaters have some heating element in them. They run on electricity, propane, or natural gas the last two are sometimes interchangeable) and use that to heat up whatever device they use to heat the water often heating coils or radiant heat from a flame, but sometimes quartz crystals and other more esoteric means)

Once the heating element has heated up, it begins heating the water as it comes through the pipes that pass through the heater box, flashes boiling the water in the milliseconds it takes for it to pass through the small heating area.

You can set your temperature at whatever you want (though the colder the water is naturally, the more powerful of a heater you’ll need to crank it up) and when you turn on a faucet, it starts heating the water as it runs. This means there’s usually a bit of a delay between turning on the water and warm water coming out, but it also means you’ll always have hot water available.

Depending on the type of water heater you have (and where you’re installing it) this process changes slightly, but the basic idea is the same no matter what.

Now, one last thing before we get into the reviews proper:

Some Ground Rule:

So many of these units share space, and I want to give a lot of good ones to shine, so here’s the main rule:

Each group (the best from all products available and our winners by brand) will only appear on this list once.

While they may be strong contenders for multiple categories on what size to choose, it wouldn’t be beneficial if I just put the same 15 units on here a few times each, would it?

Now, without further delay, here are the reviews of the best tankless water heaters.

15 Best Tankless Water Heater Reviews

1. EcoSmart ECO 27 Electric Tankless Water Heater – Best Overall

This is the model I use myself, for my home and office. It has the highest power on the market, and it’s an excellent electric model that’s cheap and perfect for a high demand of hot water between multiple applications.

Where I am (warm groundwater, low water usage) it gets me roughly 3.5 GPM and 115 degrees of heat (~30-45 degree rise), which is perfect for my needs. Better, it fits in a tiny broom closet (17” x 17” x 3.75”), so I don’t need to dedicate much space to it.

While there are other, better, more powerful units around, most are much more expensive (this one is generally under $500 from most vendors), and it has one of the best cost to effectiveness ratios around. I highly recommend this for any small business that needs hot water fast…but not for anyone else.

It just doesn’t have the power to service a more significant business or home that has massive water needs, or anywhere that’s unusually cold (you just won’t get much out of it there).


  • Compact size saves valuable storage space

  • Savings of up to 50% on water heating costs

  • Designed for efficiency, durability and easy replacement

  • 99.8% Energy efficiency

  • Limited lifetime warranty


  • Customer service is not good

2. Rheem 240V Heating Chamber RTEX-13 Tankless Water Heater

As a whole home model, it kinda flops. But as a point of use, it EXCELS. For most units, I wouldn’t give the benefit of this doubt, but since the price lies in the range of a point of use as well (usually under $400), I’ll let it slide.

It achieves roughly 3 GPM at a 40-degree rise, perfect for what a point of use should be used for: Heating a single sink or shower. This makes it an excellent install for a restaurant looking for a cheap way to heat their water, or someone with a small apartment with a single sink and shower in it (as long as both aren’t running at the same time, it will do you just fine).

Is it the best model? No. But for a particular type of person, it can be the best model for you.


  • Easy installation

  • Self-modulating power control

  • 99.8% energy efficient

  • External adjustable digital thermostatic control with LED display


  • Not the best unit for larger households

  • Not a unit for the coldest climates

3. Stiebel Eltron Tempra Plus 36 kW Tankless Water Heater

Aha! We found an electric model suitable for cold weather. It’s a bit pricier than most others here (generally set you back around $800 from most sellers), but it’s entirely worth it if you live somewhere with cold groundwater. Even at freezing temperatures, it can heat your water up to 105 degrees while still outputting 3.6 GPM.

That’s impressive for any model, but for an electric heater it’s doubly so; as mentioned before, they lose most of their heating power in cold weather.

In warmer weather, it’s an absolute powerhouse, getting 7.5 GPM when it only needs to raise the temperature about 40 degrees. For its price, that’s entirely phenomenal, with most units with that performance or above being nearly double the cost.

Its main downside is it lacks many of the extra features that can act as selling points for certain heaters (like wifi or remote controlled temperature heating, or being able to hook multiple units together), and lacks the raw power of certain Rinnai or Noritz models that make them successful commercial models in heat or cold, it’s still perfect for large residential and small to mid-size businesses.


  • Most technologically advanced heater in the market

  • Sleek design fits anywhere

  • Save at least 15-20% of your electric bill

  • No venting required


  • Not budget-friendly

  • Professional installation is needed

A little preface here before the next segment: Just about any commercial (and most residential) tankless water heauter worth its snuff is going to be manufactured with two “sub” models of any model they produce. Any model with a natral gas unit is also going to have an (otherwise identical) unit that is powered by propane instead. However, there are some that fall into only one category or the other. When one with dual functions appears I’ll point out it has equivalent propane or natural gas (whichever is opposite) model, but not repeat them on the list. With that out of the way, onward!

4. Noritz NRC1111-DV-NG Direct 11.1 GPM Tankless Water Heater

Rinnai rounds out our trifecta of well known, well-respected names in the business. Rinnai, in particular, is known for being high performance (many of their residential units double as commercial/business oriented units), high quality…and high price.

This unit is no exception, hitting 9.4 GPM at a 35-degree rise and 8 GPM at a 50-degree increase. While it also runs on natural gas, it burns much, much hotter than the last two on this list with a max BTUh of 199k. This makes it far more suitable for cold weather options since even at a 100-degree rise you can still get a respectable 4 GPM out of this beast.

It comes with a digital controller and operates at an 83% efficiency. Keep in mind that Rinnai units are generally going to be pretty bulky; this one comes in at 9.3” x 14” x 23”, so it’s going to jut out quite a bit from your wall.

Now the sticking point: The price. While close to $1400 might give some sticker shock, it’s what you can expect from Rinnai units. They eke out as much performance as they can, and charge accordingly.


  • Super efficient tankless condensing heater

  • Increases the heater’s efficiency level to over 93%

  • Ideal for reducing carbon footprint

  • Self-diagnostic onboard computer system


  • Expensive

  • Takes a while for you to have hot water

5. Rheem RTGH-95XLN Prestige Tankless Water Heater

This one is an outdoor unit that runs on natural gas, though it does have an indoor version as well. It prides itself on having very low NOx emissions, making it safer and more eco-friendly.

Regarding power, it’s pretty good, touting a 9.8 GPM at a 30-degree rise…though it should be noted that this has a RAPID drop off, falling already to 7.4 GPM at a 45-degree surge and continuing that trend downward the more heat you need.

This heat loss is likely because it is a non-condensing natural gas model (which have around an 80% efficiency most of the time; this one comes in at 82%). This means even though it has a 199k maximum BTUh, it’s effectively only 163k BTUh. It’s still better than 140k BTUh units, but only slightly.

This means it’s great for warm and moderate weather but falters significantly in extreme cold. If your groundwater is below 40 degrees on average, skip this one. For everyone else, somewhere in the range of $900-$1100 is a very fair price for what you get.


  • Easy installation and maintenance

  • Comes with safety features to prevent overheating

  • High energy factor at 0.83 (or 83% efficiency)

  • Energy saving and compact


  • Cost more

  • Not good for coolder areas because pipes can get frozen

6. Takagi T-KJr2-IN-NG Indoor Tankless Water Heater

This one also comes in an outdoor model, and in propane, making it one of the most versatile units out there. It also has some of the best performance for its price range.

Again, it is more a warm weather option, however; it’s a non-condensing natural gas unit with 140k BTUh (and only 80% of that transfers to the water). But for the right person, this is hard to beat model.

In warmer climates it can get up to 6.6 GPM with a 30-degree rise, so for its price tag of a bit over or under $500it is an excellent budget option for almost anyone who doesn’t need an overwhelming heat output.

That lack of cold weather support puts it lower on my list, but it makes a great alternative to the EcoSmart 27 mainly if you already have a natural gas line or propane hook up for your heating and have no desire to switch to electric.

That makes it a nice option, but its combination of price, performance, and flexibility is what earns it a spot on my list.


  • Most versatile unit

  • Compact size fits anywhere

  • Quite affordable

  • Designed observing safety precautions


  • Not a good option for large house

  • Limited warranty applied only if there is professional installation

7. Rinnai RL94eN Natural Gas Tankless Water Heater

This wrong boy clocks in at a base 9.4 GPM at a 30-degree rise, dropping to 8 GPM at 50 degrees (and scaling at about that rate the hotter you need to go, capping out at 4 GPM for a 100-degree rise). Like many natural gas units, it also comes in propane flavor (side note: Do not try to eat or drink propane. It’s not healthy.).

It is a non-condensing unit and ekes out an 83% efficiency rating; slightly higher (by a percent or three) than other non-condensing units.

It can also be digitally controlled, like many Rinnai units so that you can fix any temperature deficiencies from the comfort of your home; always a nice feature to have.

Now for the two main downsides: Bulk and price.

It is a pretty broad unit (9.3” x 14” x 23”), and an odd shape at that, being quite long but relatively slender, and about twice as thick as other units (meaning it juts out from your wall those 9.3”). Almost as significant is its price: In the ballpark of $1400 from many vendors, which is what ultimately makes the next water heater on our list edge it out for the victory in the natural gas category.

Sorry Rinnai, make way for…


  • Save 80% on energy

  • Easy to setup and install

  • Compact design

  • Get you hot water fast


  • Bulky

  • Yearly maintenance is a must

8. Takagi T-H3-DV-N Indoor Tankless Water Heater

Takagi T-H3-DV-N

And our winner is Takagi! Just edging out Rinnai in this category, for reasons that will soon become apparent. It’ll run you about $1200, give or take, but what it does more than justifies the cost.

It can output 199k BTUh of heat, and unlike some of the others on this list is a condensing model, putting its efficiency at over 98%; very nearly as good as an electric model. It can hit temperatures of up to 185 degrees, with a base 10 GPM.

This reduces to a still respectable 6 GPM in colder climates, making it useful for an all-weather option for both commercial and residential use (though smaller businesses mostly, 1-2 floors and four bathrooms at most).

On top of that, it comes bundled with a load of safety features and considerations, including “ultra-low” NOx emissions, freeze protection, overheat protection, and automatic emergency shut-offs!

For someone looking for a powerful (but not too compelling) machine with a lot of useful safety features, at a relatively bargain price point, you can’t go wrong here.


  • Ensure durability and longevity

  • Compact and saves space

  • Computerized safety features

  • Very low NO2 emission levels


  • High installation cost

  • Slow in providing hot water at first

9. Ecotemp L10 2.6 GPM Portable Tankless Water Heater

I love the sheer chutzpah of this thing. It’s a portable water heater with more juice than some residential, permanent fixtures, able to output 176k BTUh of heat, and can handle 2.6 GPM at max. That’s pretty insane for what it is, even if it is hampered slightly by a measly 76% efficiency (though that still puts it at 133k effective BTUh, only somewhat under most residential units).

It runs on propane (of course) but is ignited by a pair of D batteries, and is mostly meant to be used as an RV unit, though it is portable…technically. It’s very bulky and heavy(8” x 14” x 25.5”, and weighing in at 27 lbs.) meaning I wouldn’t suggest taking it on a hike with you, but stopping at a campground or something? You can hardly do better.

The price is nothing to scoff at either; often sold for under $300 for a portable machine more powerful than anything else in that price range? You’re going to be hard-pressed to find something better.

Thankfully, you are not me, so I do have one other that is better…with an asterisk:


  • Perfect for outdoor showers

  • Easy to setup and use

  • Works with any shower head and hose

  • Provide instant hot water


  • Can only support one household faucet at a time

  • Unable to check current water temperature because there is no visual thermostat

10. EZ Portable Propane Tankless Water Heater

This one also runs on liquid propane and is ignited by a pair of D batteries. It is also more potent in specific scenarios than the Eccotemp L10 (though between $20 and $50 more expensive than the L10 from particular vendors), managing to achieve 3.1 GPM…at a 45-degree rise.

In warmer climates, that means this thing is all around superior. It has a higher GPM, the same adequate heat, and it’s WAY more portable (26” x 14.5” x 6”, and 12 lbs lighter at a much more manageable 15 pounds). But of course suffers in colder weather, meaning it’s more for a nice shower after a long day of hiking a temperate forest or swimming at the beach, not so much for a long day of tromping through a winter wonderland or skiing in the mountains at your winter cabin.

That puts it just about tied for the L10. Better, warmer, lighter, and more efficient in warm weather…but a dud in colder weather.


  • Easy to use and install

  • Consistent and continuous hot water at a 45°F rise

  • No plug-in is required

  • Energy efficient and saves money


  • No tank hose and regulator included, need to buy it

  • Need an exhaust vent

11. Rinnai V53DeN Natural Gas Outdoor Tankless Water Heater

First off, this is a strictly warm weather option. I wanted to highlight that early because it’s primarily crucial for outdoor models: If you try to use this in colder climates, it is very prone to freezing.

Other than that, it’s pretty good. Both this and the next on this list are propane powered units that can be installed in manufactured or mobile homes; a vital niche not many models correctly fill.

It’s a reliable 82% efficient with 140k BTUh, and a 5.3 GPM in ideal conditions (only need to raise the temperature by about 40 degrees), and perhaps most importantly: Touts itself on being very easy to install.

That’s impressive performance and convenience for something often sold for under $600, but if you’re looking for something a little stronger, the V53 has a brother that lifts:


  • Compact design

  • Affordable

  • Use 40% less energy than traditional tanks

  • Combination of high efficiency, comfort and value


  • Need to wait for a while to have hot water

  • Cost expensive in repair

12. Rinnai V65EP 6.5 GPM Outdoor Tankless Propane Water Heater

While Rinnai V65EP will run you a bit more (usually a little over $700, sometimes less), it’s also a much better unit all around if you have a larger budget.

It has a 6.5 GPM and a 150k BTUh heat output, making it stronger and better in all regards than the V53.

While this one also has no freeze protection, it also has an advantage over its brother: It has an indoor unit variant, meaning if you buy that kind it won’t have the same issues with freezing. Still, it is a better warm weather unit so I’d stick with one there unless you have no other choice (though living in a mobile home or trailer does limit your options some).

Still, for all its downsides you can do a lot worse than 6.6 GPM for less than $1000, and its versatility (indoor and outdoor install, propane or natural gas hook up) makes it a sort of all in one for those needing something they can easily install in their trailer home.


  • Compact and Easy-to-install

  • Reliable and perfect for outdoor locations

  • Use less energy and conserve water

  • Smart technological advancements such as WiFi monitoring


  • Have to wait for a while for the hot water

  • Repair Cost expensive

13. Rheem RTGH-95DVLP 9.5 GPM Tankless Water Heater

It is a 9.5 GPM (at a 35-degree rise; 8.4 GPM at a 45-degree surge) condensing machine, making it a 94% efficient heater (which is a bit low for a condensing heater, but still better than any non-condensing machine). It will often run you between $1000 and $1500.

The RTGH-95 has freeze protection to -30 degrees, which makes it one of the better cold weather options out there, heating aside (though the heating is right in that scenario as well), and does come with remote and digital tuning.

It prides itself on something we don’t talk about much: minimum flow rate. While a significant figure, the vast majority of tankless water heaters operate at .6 GPM to .8 GPM at a minimum (meaning if there’s something wrong with your water, or you’re just trying to run a trickle, it’s not going to heat up correctly). This Rheem kicks on at a .26 GPM to .40GPM minimum flow, nearly half the average. This is great if you need to run a shallow volume sink or something.

It’s the features that win this. Most tankless water heaters run in pretty predictable ranges of efficiency, heat, and GPM which this one meets for the higher end models quickly; it just goes above and beyond, which also neatly brings us to our next category…

This section is going to be a bit different. Many of these units will be ones we’ve already talked about, so for those, I will be explaining exactly why it beats out other competition in its brand, for the most part.

For companies we haven’t talked about, I’ll give a bit more detail and the specs for their best units.


  • 94% Energy efficient

  • Easy installation

  • Special low-NOx system reduces fumes and emissions

  • Smart technological advancements


  • Quite pricey

  • Minimum flow rate of 0.26 GPM

14. Sio Green SIO18 v2 Infrared Electric Tankless Water Heater

Sio Green SIO18 v2

I just like how this thing works. It doesn’t use heating coils like most other units to heat the water. Instead, it uses quartz crystals.

It heats the crystals up (to around 200 degrees), and they radiate heat into the water without ever touching it.
This one’s a good choice just for the novelty of telling people you have a water heater that shoots lasers into your water, but besides that, it’s also only a functional unit for warmer climates.

Outputting 4.0 GPM with a modest 30-degree rise, and 2.5 GPM with a 60-degree rise, its usage depends on location. 4.6 GPM is quite good for the price (often hovering around $800), and I recommend it if that fills your needs, as the benefits of a non-corroding unit cut the hassle and cost of maintenance significantly.

However, that’s just too pricey for 2.5 GPM; you could easily buy a point of use unit that can do the same job for under $300 at that point, so it’s not worth it if you live somewhere cold.


  • Compact design

  • No venting required

  • No maintenance needed

  • Offers refund or replacement if not 100% satisfied


  • Pricey

  • Professional installation needed

15. Sio Green IR260 v2 POU Infrared Electric Tankless Water Heater

Sio Green IR260 v2

One more point of use model before we get to our winner. This one again from SioGreen, with the infrared quartz crystal based heating source.

This one is much smaller, only handling about 1.5 GPM at 30-degree. This makes it flow very light for regular use…but in an RV, that makes it quite useful. It’s small, and its power drain is relatively low, so installing it in an RV, or somewhere else where low water flow is expected is the perfect use for this little beauty.

My main issue is it’s a reasonably large unit for what it is (13.5”x8.5”x3”), but that’s a minor gripe for something that will set you back less than the price of an Xbox One, relatively efficient, cool little water heater. Again, is it the best for everyone? Not.

But it’s the best for SOMEONE, which makes it all right in my book.


  • Operational Longevity

  • Superior Heating Efficiency

  • No Maintenance required

  • Adjust to your exact needs


  • Suitable for low flow applications

  • Not suited for installations with multiple fixtures

Top Pick By Brands

1. Rinnai C199EN

Rinnai C199EN

The Rinnai C199 models are as good as it gets. While a bit pricey (it’s almost always going to cost you over $1600), their combination of efficiency just over their competitors, consistent power in all weather, and (probably the most prominent factor that helped it pulls a small victory over the top two competitors), easy adjustment for heavy commercial use that allows linking multiple units together.

What this does mean though is this: While this is, in my opinion, the best overall unit, from a purely residential perspective, for the average person with a medium sized home, the Rheem RTGH-95DV beats it. But I value being used in multiple settings here, and in that regard, the Rinnai C199 models are unmatched in power, features, and versatility.


Rheem is one of the most respected brands in the business, and it’s easy to see why. They provide a wide range of top quality models at what I feel are fair prices. While a Rinnai beat them, they (in my opinion) give a much better mix of value to performance across the range of their models than any other company on this list.

No option in their catalog exhibits this more than the RTGH-95DV models, in my opinion, having high performance at a price that doesn’t bust the bank, and features that most brands and models struggle with (particularly the freeze protection). The main reason the Rinnai C199 beats it is that it ekes out just ever so much more efficiency and power than this Rheem that I felt it was the best all around, even if it comes only to the edge of where I’d say fair pricing for it ends.

This is a solid second choice, and if you need to save a few hundred bucks, you can’t go wrong with this one, mainly for residential use.

3. Takagi H3-DV-N

Takagi T-H3-DV-N

Don’t let this placement fool you, this was a close race, with all three coming in very, very close to each other. They’re very nearly a tie in every regard, all three having somewhat similar performance, and certain ones having specific features that recommend them to others.

In this case, the T-H3 sits at the top 3 because of the three it makes the worst commercial option, whereas the Rheem and Rinnai winners perform admirably as both residential and light commercial (for the Rheem) or medium business (for the Rinnai).

For the safety conscious person in colder climates looking to heat the water in their home, the Takagi is the clear winner, but the added versatility in the usage of the other two edges it out.

4. Ecosmart ECO 18

While it’s not the most potent unit Ecosmart has (that would be the Eco 36), it has the best power to cost ratio in my opinion, and it gets an edge out of the slight bias I have for owning and using it daily.

Ecosmart in general just makes good stuff. There are more powerful units out there, but particularly in the realm of electric groups (which are relatively sparse in the selection, to begin with), it stands out as a good heater, with a high price tag.

5. BOSCH Tronic 3000

Bosch Thermotechnology has a tiny selection, all of which is a small point of use models (many of which are little water heater tanks, not tankless water heaters). However, their 3000 series are pretty reliable (and very, very cheap) models.

All are electric, and run off 240v of power save the 3.4 kW model which runs off 120v. All are also the same size (6.5” x 12.25” x 3”), and 98% efficient.

They come in four variants, ranging in price from under $150 to a bit under $200 from most sellers:

  • 3.4 kW: .5 GPM at a 45 degree rise.
  • 7.2 kW: 1.1 GPM at a 45 degree rise; .7 GPM at a 75 degree rise.
  • 9.5 kW: 1.4 GPM at a 45 degree rise; .9 GPM at a 75 degree rise.
  • 12 kW: 1.8 GPM at a 45-degree rise; 1.1 GPM at a 75-degree rise.

As you can see, they’re not precisely powerhouses (and wouldn’t quite make my cut under normal circumstances), but for the price the 12 kW model is a good buy if you just need to power a single sink in your garage, tool shed, or similar workspace.

6. EEMax HA008240

Eemax HA008240

Like Bosch, Eemax is a relatively small brand that mostly makes a low point of use heaters. Unlike Bosch’ 3000 series though, this little guy has a bit of power to it, with a max of 3 GPM instead of under 2 GPM like the 3000s.

14” x 18” x 4.5” is…quite large for a point of use model, but the price isn’t, usually sets you back under $200. I’m not sure I’d wholeheartedly recommend this unit, but I wouldn’t advise against it either. It’s a solid middle of the road model that could be the perfect fit for someone with reduced water usage needs at a single space, like an industrial sink or chemical shower or something.

While it wouldn’t be my first recommendation if I were talking to someone in person, it also wouldn’t be my last; if somebody said they wanted a small, cheap point of use device this would be close to the top of the short list for models that fit the bill and perform the job well.

It might be a lesser known brand, but that doesn’t change that this is a quality model.

7. Noritz EZTR40NG

Noritz EZTR40NG

Suffice to say I like this model, and I love Noritz’ general design philosophy: Function over form.

It’s not pretty, and it doesn’t have the bells and whistles of other competitors but it’s got a lot of power in a lot of situations, for a reasonable price, and that deserves respect on its own.

The main thing is, other competitors have similar or better performance…and ALSO bells and whistles and a slimmer design you can better fit in specific spaces, which edges it off the top spot. But still, this model (and company) are a great option if you feel like saving a couple of hundred bucks on stuff you may think is unnecessary.


This is natural gas or liquid propane unit with 150k BTUh of heat output, and a max 8.4 GPM at a 35-degree rise, torquing down to 3.8 GPM at a 77-degree increase. It is a condensing model with 98% efficiency and low NOx emissions. This makes it a solid middle of the road option, but…

The main issue is I can find very few sources of information about Navien, making personal opinions on the thing scarce enough that I hesitated to put it on the list, and ended up dropping it because best case scenario, there are better documented Rheem, Rinnai, and Takagi models on the market with similar or better specs anyway.

Mainly since it falls in the roughly $1100-$1200 range, there’s too much competition for me to wholeheartedly recommend this one without a better sense of how it stands up in actual use. While the specs sometimes speak for themselves, I like to have SOMEBODY’S word to stand behind it besides the company’s; a customer review can often bring to light issues in construction or fragility in the long term that just would not be listed in a seller blurb.

Similar model: Navien NCB 240 Review

How Do I Pick The Right Tankless Water Heater?

1. Traditional vs. Tankless

Let’s take a hot (heh) second to explain why you want to go tankless over a traditional tank, the primary reason being:

You’ll always have hot water. Tankless heaters don’t “run out” because they don’t store water, they just heat is as it comes through. As long as you have water in your well or are correctly connected to the city’s system, you’re golden. It also doesn’t hurt that you’re saving money in the long term. My step-mom used to turn off the water heater any time it wasn’t in use to save some cash, but it took 30 minutes to an hour for the water to heat back up after that.

A tankless water heater combines cost-saving idea with convenience: You don’t have this device running all day long, but you also don’t need to wait forever after turning it on to get your hot water.

Read More: Tankless vs Tank Water Heaters

2. Fuel Type

You’ve got three primary ways these heaters are powered:

  • Electric 

that pull either 120V or 240V of power to heat coils to heat your water. These lose about 2/3 of their effectiveness in areas with cold groundwater but are often cheaper.

Read More: Best Electric Tankless Water Heater

  • Propane

which is like natural gas, but for when you don’t have a dedicated gas line and need to bring in an outside source. Most natural gas heaters come in a variation that runs on propane instead; there are very few that are strictly one or the other. 

In general:

  • Is more expensive
  • Needs schedule deliveries
  • But is also more efficient (it’s twice as efficient, in fact)
  • Is not a greenhouse gas, so is more environmentally friendly if it leaks into the atmosphere (though both it and natural gas BURN cleanly)
  • Natural gas

which hooks into your gas line to heat water pretty much the same way you’d boil water on a gas stove (but way hotter, and way faster).

Natural gas and propane are roughly equivalent in the grand scheme, though each has a few merits over the other.

In general:

  • Is often cheaper
  • Does not need scheduled deliveries (it’s piped in as long as you pay your bill, just like any other utility like electricity or water)
  • Burns less efficiently (though the cheaper cost makes this point mostly moot)
  • Is a greenhouse gas, and less eco-friendly if it escapes into the atmosphere somehow.

Which you choose is mostly a matter of what your home or business is already set up for. If you’re already set for one or the other, swapping to the opposite will be costly and mostly pointless.

3. Gas vs. Electric

Here’s the main difference:

Electric models are usually weaker than the gas models, made for smaller homes or offices, or prepared to service a single faucet at a time.

My electric model works for me just fine, but if you like to run things concurrently (like shower, wash clothes, and wash dishes at the same time) or have a large house (in size) or household (i.e., people) and multiple showers are running at a time, for example, a propane or natural gas model will probably be your best bet.

Likewise, be aware that electric models usually lose about 2/3 of their efficiency in cold climates. I live somewhere where the groundwater is already above 70 degrees so this isn’t an issue for me, but it can be a deal breaker if you live somewhere the water is usually below 40 degrees.

Likewise, be aware that electric models usually lose about 2/3 of their efficiency in cold climates. I live somewhere where the groundwater is already above 70 degrees so this isn’t an issue for me, but it can be a deal breaker if you live somewhere the water is usually below 40 degrees.

Read More: Electric Versus Gas Tankless Water Heater

4. Cost

Here’s the deal:

A tankless water heater will cost you more up front than a tank, by about 50% or even double depending on the model. However, in the long term, energy savings are significant, and in the short time, they’re SO convenient.

Your water heater is kinda like your bed: Don’t skimp, you’ll only regret it when the cheaper option leaves you uncomfortable and dissatisfied. 

5. GPM

Stands for “Gallons Per Minute,” and is your efficient water output at a given temperature. For example, one water heater might output 3.0 GPM if it raises the temperature by 100 degrees, or 10 GPM if it only raises the temperature by 45 degrees; Another may just increase the heat by 45 degrees at 3.0 GPM because it’s weaker (and probably way less expensive). Determine your water usage and purchase accordingly.

For reference: A shower is between 2.1 and 2.5 GPM, a faucet is between 2.2 and 2.5 GPM (neither are by law allowed to exceed 2.5), a dishwasher is 1 GPM, and a washing machine is .5 GPM.

If you want to run, say, two showers and dishwasher at the same time, live somewhere cold (where the groundwater is 35 degrees) and like your shower at 115 degrees (like I do), you need a heater that can run at a 6 GPM capacity while raising the temperature by at least 80 degrees; a tall order. I’m lucky, my groundwater is already 70+ degrees before it even comes up, but for those that live in colder areas, be informed on your groundwater temperature. 

Read More: What Size of Tankless Water Heater Should You Get

6. BTU

British Thermal Units.” The temperature needed to raise 1 lb of water one degree. “BTUh” (British Thermal Units per hour) is the number that will be most commonly given.

Reference: A gallon of water is 8.3 lbs, so the BTUs needed to raise a gallon of water one degree is 8.3 BTUs.

Most commercial and residential water heaters have a maximum BTUh of 140k to 199k, while RV based units hover between around 40k and 75kBTUh and GPM are pretty closely linked; higher one usually means the other will be higher as well.

Also, read out how to install a tankless water heater guide for easy installation.

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