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5 Best Tankless Gas Water Heaters – (Reviews & Guide 2021)

It is well known that tankless water heaters save you money in the long run – even if they come with a higher initial cost. Naturally, this is not the only benefit that you will enjoy if you purchase a tankless water heater.

For starters, a gas tankless water heater can help you save an average of $108 per year, in energy costs. Of course, they do save more than their tank counterparts. If you were to choose from the best gas tankless water heaters out there, you would end up saving much more, especially if you use it economically.
But how could you be sure that you chose the best model available? Well, here is where we come and help you.

In the following lines, we’ll present you with some gas tankless water heater reviews, after which we will move on to a rather comprehensive guide. In short, get ready for all the information about gas tankless water heaters that you can handle!

Best Gas Tankless Water Heaters Comparison Chart

Rinnai RUC98iN Ultra Series

Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater

  • Price: $$$$
  • Dimensions: 10 x 18.5 x 26″
  • Weight: 82 pounds
  • Flow Rate: 9.8 GPM
  • BTU: 199,000
View On Amazon
Rheem RTGH-95DVLN Indoor Direct Vent

Rheem RTGH-95DVLN Indoor Direct Vent Tankless Natural Gas Water Heater

  • Price: $$$$$
  • Dimensions: 18.5 x 9.8 x 27.5″
  • Weight: 79 pounds
  • Flow Rate: 9.5 GPM
  • BTU: 199,000
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Rinnai RUC98iP Ultra Series

Rinnai RUC98iP Ultra Series Propane Tankless Water Heater

  • Price: $$$$
  • Dimensions: 10 x 18.5 x 26″
  • Weight: 82 pounds
  • Flow Rate: 9.8 GPM
  • BTU: 199,000
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Eccotemp i12-NG

Eccotemp i12-NG Tankless Water Heater

  • Price: $$$
  • Dimensions: 16 x 16 x 11″
  • Weight: 28.9 pounds
  • Flow Rate: 3 GPM
  • BTU: 25,000 – 80,000
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Gasland BE158 1.58GPM 6L

Gasland Outdoor Portable Gas Water Heater

  • Price: $
  • Dimensions: 11.8 x 6.1 x 17.3″
  • Weight: 15.5 pounds
  • Flow Rate: 1.58 GPM
  • BTU: 41,000
View On Amazon

Best Tankless Gas Water Heater Reviews – (Top-Picks)

1. Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater

Rinnai RUC98iN Ultra Series Gas Tankless Water HeaterThe first product on our list is the Rinnai RUC98iN, which comes with a rating of 4.5 stars. Reportedly, it is a new model from this manufacturer, capable of delivering more efficiency to its users.

The product itself is imported, with a concentric model and with the option of a PVC venting. When it comes to looks, this tankless water heater has a sleek design with a metallic finish. It fits best with appliances that have the same silver finish.

On top of that, its design is also space-saving, thus allowing the heater to be installed indoors.
It features up to 0.96 Energy Factor and up to 0.92 Uniform Energy Factor. Reportedly, the product has ultra-low NOx emissions and is capable of up to 199,000 BTU.


  • 199,000 BTU
  • Ultra-low NOx emissions
  • Up to 0.96 Energy Factor
  • It has a space-saving design
  • 95% Thermal efficiency


  • Concentric exhaust requires additional OEM parts

Read More : Rinnai RUC98iN Ultra Series

2. Rheem RTGH-95DVLN Indoor Direct Vent Tankless Natural Gas Water Heater

Rheem RTGH-95DVLN Indoor Direct Vent Tankless Natural Gas Water HeaterThis gas tankless water heater from Rheem comes with a 4-star rating, making it one of the most popular – and best – water heaters on the market. The product comes with something every buyer would want to hear, 94% energy efficiency.

On top of that, the heater has its condensing heat exchanger made from stainless steel, hence the energy efficiency coefficient. It also features intelligent electronic controls, which are specially designed to increase the heater’s energy efficiency, as well as safety.

This specific model is, as reported by the manufacturer, a low NOx version – so, you don’t need to worry about any harmful emissions. The heater is compatible with a two-pipe direct vent system that is designed for PVC pipe.


  • It features a digital display
  • The two-pipe direct vent system
  • Built-in electric blower
  • It has a digital remote control
  • It comes with freeze protection
  • 94% energy efficiency


  • A bit noisy
  • Max water temp of 120
  • Low flow turn on

Read More: Rheem RTGH-95DVLN

3. Rinnai RUC98iP Ultra Series Propane Tankless Water Heater

Rinnai RUC98iP Ultra Series Propane Tankless Water HeaterThis is the second water heater on our list from Rinnai, but this one uses propane instead of natural gas. The model features the same silver/metallic finish, making it suitable for areas that share the same colors – or just for your basement.

The product comes with a max BTU of 199,000 and with an up to 0.96 energy factor. On top of that, it has little to no NOx emissions, due to some special technology it employs.

In terms of venting, it features options for both PVC or concentric venting. It comes with a 12-year-old warranty on the heat exchanger, 5-year on parts, and 1-year on labor, with the option to increase it to 5 years.


  • A flow rate of 9.8 GPM
  • 199,000 max BTU
  • 0.96 energy factor
  • Ultra-low NOx emissions


  • Some customers claimed that it takes up to one minute for hot water to reach their faucets.

Read More: Rinnai RUC98iP Ultra Series

4. Eccotemp i12-NG Tankless Water Heater

Eccotemp i12-NG Tankless Water HeaterEccotemp has a water heater with a very pleasant design. Sleek and modern, this tankless water heater could be placed almost anywhere in your house. Its front panel is made of black tempered glass which has LED display controls as well. Kitchen or lobby – it would be a perfect fit!

The heater is whole-house and rated at 3 GPM, which activates only on-demand, and it doesn’t require any pilot light. Because of this, this product can help you reduce energy consumption.

On top of that, the fully automatic temperature controls have an energy-saving mode as well – besides the child-lock technology. This makes for an energy-efficient product.
Safety is ensured with the help of a safe electronic ignition system.


  • If features LED display controls
  • Safe electronic ignition system
  • 3 GPM flow rate
  • Horizontal venting
  • It is energy efficient


  • The exhaust can get quite hot
  • Reportedly, the installation process may be a bit difficult – a case in which you can contact the manufacturer’s customer support team.

Read More: Eccotemp i12-NG

5. Gasland Outdoor Portable Gas Water Heater

Gasland BE158 1.58GPM 6L Outdoor Portable Gas Water HeaterOur last entry is the outdoor portable gas water heater from Gasland. In short, it comes with a lot of features!
First of all, we have multiple safety systems in place, such as a flame failure device, anti-freeze protection, as well as overheating protection. If the water pressure goes above 110 psi, the heater will automatically decrease it to keep things safe.

It features a lightweight and compact design, making the product very easy to carry and mount. The back and the top of the heater feature mounting brackets that can be used to install it in a matter of minutes.
In terms of energy savings, the main burner and the propane water heater exchanger are designed with advanced combustion technology in order to decrease burning noise, as well as gas consumption.


  • It has several safety systems in place
  • It features a lightweight, compact design
  • 41/000 BTU/ hour
  • 1.58 GPM
  • Fully adjustable water and heat flow.


  • The instruction manual doesn’t refer to the use of the product’s front dials.
  • Some customers complained that the heater could use at least 2 GPM for a hot – and not just warm – shower.

Read More: Gasland BE158

What Is a Gas Tankless Water Heater?

What is a Gas Tankless Water HeaterObviously, a gas tankless water heater is a type of heater that operates on gas and doesn’t need a tank for water storage. The tankless technology was used in the past and implied water being heated and kept in a tank for later use.

Naturally, tank water heaters would run out of the water pretty quickly – depending on the hot water demand – and you’d have to wait for the gas heater to heat up water and fill the tank again.

On the other hand, tankless water heaters can provide a household with true, on-demand hot water. Basically, such devices heat water while you are actively using the faucet.
True, some models will require you to wait for a couple of seconds before being provided with hot water, but this largely depends on how efficient the said model is. Most are capable of instant hot water, while some will take up to one or two minutes before supplying you with hot water. For instant hot drinking water, please read our reviews on top-notch instant hot water dispensers.

When it comes to fuel, gas tankless water heaters will heat water with the help of either natural gases or propane, depending on the model of your unit.

How Efficient Are Gas Tankless Water Heaters?

First of all, gas tankless water heaters are very efficient mainly due to the fact that you do not have to constantly pay to keep your water hot. You would have done this if you had a tank model installed in your home.

Given that tankless models start heating water only when you open a faucet, you spend no money while you are not using hot water.

Moreover, tankless units come with a longer lifespan, in terms of both units and components. With yearly maintenance, you will most likely not change your current unit in the following 15 to 20 years. Also, regular maintenance will keep the tankless water heater efficient. Ultimately, natural gas/propane is cheaper than electricity. Moreover, while gas is believed to keep a steady price in the upcoming years, analysts think that electricity will see a surge in costs.

Long story short, there are gas tankless water heaters that can reach 96% efficiency, while most of them do not go lower than 87% efficiency. Therefore, if you choose your water heater properly, you will end up saving money and enjoying an efficient product.

Gas Tankless Water Heater Buying Guide

Now that you know the basics of gas tankless water heaters, it is time for you to make a purchase.
However, if you think that the models that we’ve talked about earlier don’t fit you or your needs, this means that you will need a tad more information in order to make a wise purchase.

Therefore, in the following lines, we’ll tell you everything that you need to know about gas tankless water heaters. In the end, we hope this information helps you make a wise and proper purchase!

What Should You Consider When Buying a Gas Tankless Water Heater?

As expected, it is not easy to buy a gas tankless water heater. You have to take a lot of things into consideration before being able to say that you finally found the perfect fit for your home.

On top of that, you might also want to consider the design and ease-of-use of your future water heater, especially if you want to place it on sight and use it as additional home decoration, so to speak.
In any case, we are here to answer every question you may ask when buying a gas tankless water heater.

  • Power Input

    In terms of tankless water heaters, power and size are relatively equal, so to speak. For example, you will need a water heater with a size that can offer your household enough hot water.

    In addition to that, you will need a model that is powerful enough to effectively increase the water temperature and bring it to what you and your family want. In short, you have to make sure that the water is hot enough to satisfy both your needs and expectations.

    To make sure you choose the right water heater, consider this – the more power, the better. For example, small spaces will require as little as 10,000 BTU’s, while large – or commercial – ones may require as high as 1,000,000 BTU’s.

  • Flow Rate

    The power input of the heater handles the right temperature. Flow rate, on the other hand, is what determines the amount of water the heater can deliver to you.

    The flow rate should be chosen according to how many devices you have in your home, or you want to power. For example, if you want to supply a single faucet with hot water, then a flow rate of 1 GPM should be enough. However, if you want to supply all of your water-based appliances – or your entire home – with instant hot water, then you will need a heater capable of more than just a couple of gallons per minute. We’ll talk more about this issue when we show you how to properly size your gas tankless water heater.

  • Venting

    Obviously, venting is an important part of every indoor gas water heater – be it tankless or with a tank. The heater eliminates hazardous gases that must be eliminated and then removed from the property. A venting system will ensure additional home intake from the exterior, if necessary. Gas tankless water heaters usually come with two venting options:

    • Power Venting – this type of venting requires an exhaust pipe. Before you install such a venting, make sure that the installation area has a fresh air circuit.
    • Direct Venting – this type of venting requires an exhaust pipe, as well as an intake pipe. The exhaust pipe gets rid of all carbon monoxide and hazardous gases, while the intake pipe ensures sufficient air intake.
  • Energy Factor

    The energy factor of every gas tankless water heater can help you calculate the unit’s energy efficiency. Basically, you will learn more information about the heater’s average cost of operation.
    In order to come up with the annual operation cost of a water heater, you have to multiply the fuel cost by 41045 and then by 365. Lastly, the end result will have to be divided by the unit’s energy factor x100,000. Keep in mind that most units do have their energy factors listed in the product description.

  • Condensing and Non-Condensing?

    It is well known that condensing gas tankless water heaters can save you a lot of money on installation. On top of that, they will become more energy-efficient and emit exhaust air that’s cooler than non-condensing models.

    Moreover, condensing water heaters can also use PVC – instead of metal – which can really make a difference when it comes to expenses. On the other hand, non-condensing water heaters are perfect for outdoor placement. These models are usually cheaper, as well as slightly smaller. Reportedly, they represent a perfect fit for cabins, mobile homes, and even camping.

  • Other

    Naturally, you will want a product from a reputable brand. Not only that these last longer but this also ensures the fact that the manufacturer will respect the warranty. There have been some cases in which certain brands seemingly did their best to nullify a customer’s warranty.

    Furthermore, you will want to pay attention to certifications. For example, if you want to install the heater in a mobile home, you may require certain permits, depending on the state. Lastly, if you desire increased convenience, you may want to buy a model with a thermostat and remote control.

The Most Important Gas Tankless Water Heaters Features and Specifications

Best Gas Tankless Water HeaterIn the following lines, we’ll introduce you to a list of the most important features and specifications that a gas tankless water heater should come with.
Make sure that you are able to tick as many features as possible before you purchase a certain unit. After all, more features and specifications, associated with a reputable brand, can make for the best gas tankless water heater.

  • Suitable Gallons per Minute – Water Flow
  • Exhaustion Properties – Proper Venting System
  • Condensing/Non-Condensing
  • Anti-Freeze/Cold Safety
  • Warranty on Heat Exchanger/Parts/Labor
  • Energy Factor that results in a low annual operation cost
  • Required Certifications
  • High enough power input

All of the above, depending on your choices, can either make or break your future purchase. It is very important that you take your time to properly choose the gas tankless water heater that will soon have to provide your home with hot water.

Now, to make sure that your purchase is even more well-informed, let’s move on to how you size a gas tankless water heater. Proper sizing will also make you tick a lot of the features and specifications we’ve just mentioned!

How to Size a Gas Tankless Water Heater?

As mentioned above, the size of the water heater is extremely important and should not be taken lightly. The proper unit will be able to ensure maximum efficiency while making sure that you don’t spend more than you should on the installation, usage, and the heater itself.
To properly size a gas tankless water heater, you will need to take into account two things – namely, the flow rate and the temperature rise.

  • Flow Rate – Number of Devices that the Heater will Cover

    Obviously, you will have to take into account all bathroom and kitchen faucets, shower heads, and persons within your household when determining the size of the water heater. All of your water-based appliances have to be considered!

    Each of the above will come with its own flow rate, which you will need to add up to determine the flow rate that your future water heater will have. For example, showers and tubs usually spend around 2.5 to 4 gallons per minute, while the average faucet spends around 0.75 gallons per minute. If you plan to run more than one appliance at the same time, make sure that the heater’s flow rate can keep up.

  • Temperature Rise

    Then, you will have to consider the current water temperature and, most importantly, the preferred output level. The current water temperature will usually be around 50F and most people want their water warmed up to roughly 115 degrees.

    This means that you will need a heater powerful enough to make for a temperature rise of 55 degrees. A less powerful heater will obviously come cheaper, but it won’t be able to heat up the water as much as you’d like. In short, don’t compromise when it comes to expenses or you may be showering in unpleasant, lukewarm water.

Types of Gas Tankless Water Heaters

When it comes to the types of gas tankless water heaters, you will have to choose between condensing, non-condensing, and – in some cases – condensing hybrid. We’ve mentioned this aspect earlier but didn’t go into too much detail.
Now is just the time to tell you everything that you should know about the three types of gas tankless water heaters.

  • Non-Condensing

    The non-condensing units heat water on-demand using a heat exchanger and can reach an efficiency factor of up to 0.85. This is a well-proven technology that has been used in Japan and Europe for decades.
    The main advantage of non-condensing units is that they are very reliable, mainly due to the fact that they’re established products and have few to no manufacturing issues.
    However, such units do come with drawbacks. For example, the exhaust can get quite hot, requiring you to install additional stainless-steel vents and decrease the overall energy efficiency.

  • Condensing

    Condensing units, also known as the second generation of tankless water heaters, use a secondary heat exchanger after their primary one. The secondary one reuses the heat from the exhaust to heat the water even more.
    As a result, the efficiency increases by up to 94%. The main benefit is that such units can be safely vented using PVC. The drawbacks include a higher cost per unit, as well as lower efficiency in short water draws. For example when washing your hands.

  • Condensing Hybrid

    These types of units incorporate a small water storage container – usually around 2 gallons. This tank will keep a reservoir of hot water, thus eliminating the efficiency lost for short draws. Basically, this makes for a water heater that can reach an energy efficiency of 0.96.

    Studies have shown that condensing hybrid units can consistently operate at 94% efficiency with almost no degradation caused by short draws. Such units can be vented using PVC as well, making them less expensive.

    However, because condensing hybrid units are a newer technology, they are mostly manufactured by small companies. This results in warranty and manufacturing-quality issues.

The Pros and Cons of Gas Tankless Water Heaters

Naturally, every product out there comes with both pros and cons. When you choose a product for purchase, you will have to determine whether the pros are worth it or if the cons are not that significant.
Let’s see what the advantages and disadvantages of tankless water heaters are;Benefits of Gas Tankless Water Heater


On-Demand Hot Water

Tankless units are known for their ability to deliver instant, hot water.

Energy Efficiency

As mentioned above, gas units can reach even 96% energy efficiency, making them some of the most efficient water heaters on the market. This means saving money on bills!

Increased Lifespan

While tank units can last for up to ten years, tankless water heaters can provide you with hot water for up to twenty years if serviced properly. Even if they are more expensive initially, tankless units help you save money in the long term.


Tankless units are much, much smaller than tank units, and can be placed virtually anywhere. However, it is recommended that they are close to your main water-based appliance in order to reduce hot water lag. Still – you could place a tankless unit anywhere in your home.

Environmental Impact

Even though they run on gas, these units have a reduced environmental impact. First of all, they require less energy to work and, unlike tank units, produce fewer greenhouse gases.

 Standby Losses

Tank water heaters need to reheat the water continuously in order to keep its temperature high while in the tank. Naturally, this makes for a bill that you don’t want to see. On the other hand, tankless units will heat water and consume gas only when you turn on a faucet/shower.

Ideal for Smaller Homes

Tank units didn’t always fit the home of their buyers. Most of the time, people simply said goodbye to hot water mainly because they didn’t have any room left for a tank heater. Obviously, tankless heaters – with their low GPM models – are ideal for one- or two-faucet homes.


High Initial Cost

Traditional heaters cost around $500. On the other hand, a tankless unit will cost you $1,000 or more. Moreover, they also require a professional to install them. On top of that, gas/propane models will also require you to retrofit the venting system of your home – this is not necessary with electric tankless water heaters.

Fluctuations in Temperature

Due to the fact that they have to heat the water on the go, tankless models are usually subject to temperature fluctuations. This issue usually comes up when multiple faucets are being used and the water heater simply can’t keep up with the demand.

Extensive Retrofitting

Obviously, gas tankless water heaters will require you to retrofit the venting and gas systems of your home, as mentioned above. This is because gas units are usually not compatible with the piping and venting in most homes. In the end, you will most likely have to add new venting and even reroute gas lines.

Extra Equipment

Depending on the water you are supplied with, you may need a softener that reduces water hardness. A water softener will not only increase the overall costs but will also take a lot more space than the heater itself.

The Costs Involved by Gas Tankless Water Heaters

While electric units will cost around $1,500 to install, a gas tankless water heater may cost you as much as $3,500 to install. This is because gas models require venting, as well as additional safety measures. After all, you are dealing with either natural gases or propane, which can be very dangerous.

  • For example, natural gas is widely available and comes with an annual cost of $163. To install a gas tankless water heater, you will need to pay an additional $429.
  • On the other hand, propane is widely available and has an annual cost of $163. However, installing such a model in your home will require a payment of $498 in install costs.
  • When it comes to labor, a gas water heater comes with costs of around $1,200. Naturally, you do have to take into account the additional gas line – that’s an extra $500.
  • Moreover, permitting will also cost you between $250 and $500, depending on where you want to install your gas tankless water heater.
  • You will also have to service your heater yearly – this makes for up to $130/year in maintenance costs.

Obviously, the installation cost of a gas tankless water heater will be the one to probably push you away from such products. However, keep in mind that these models can actually save you money in time.
Given their energy efficiency and technology that does not waste any water or fuel, you may save up to $200 per year – depending on usage and hot water demand.

The Installation and Maintenance of Gas Tankless Water Heaters

Gas Tankless Water Heater ReviewsBefore reading any further, keep in mind that installing a gas tankless water heater is a very difficult process and requires a professional, especially if you don’t know how to handle some of the following steps.

Unless you are extremely sure that what you are about to do is correct, it is highly recommended that you contact a professional.

Installing a Gas Tankless Water Heater

For the installation of a gas tankless water heater, you will need spade drill bits, power drills, adjustable wrenches, screwdriver sets, torches and tanks, and reciprocating saws. Moreover, you will need pipes, valves, gas fittings, gas connectors, tankless gas, black pipes, caulk, and sealants.

  • Install a New Gas Line – if your current gas line has the proper size, then install a valve and/or a tee in the existing line. Then, run a new gas supply line to the point where it can be attached to the heater.
  • Install New Water Lines – you have to tie in new cold and hot water lines with copper pipe and run them to the new heater.
  • Mount the Water Heater – choose a suitable location for your heater and, if required, build a platform for it to stand on.
  • Connect the Water Heater – use the manufacturer’s instructions to make sure that the connections have been made properly.
  • Install the Vent
  • Turn on the Water Heater – open any faucet to full “hot” in order to purge any air left in the water pipes and heater. Remember to insulate the hot water pipe coming out of the water heater.

How to Maintain a Gas Tankless Water Heater

Now that you know how to install a gas tankless water heater, it is time to learn how to maintain it.

  • Turn the gas tankless water heater’s power source off.
  • Close and turn on the three water valves that are attached to the heater.
  • Remove the caps of the purge port valves located on each of the hot and cold water valves.
  • Attach hosing lines to each of the three valves.
  • Open the purge port valves via perpendicular twists to the position of the hot and cold valves.
  • Use roughly 2.5 gallons of undiluted white vinegar when cleaning the heater – avoid using chemical solutions.
  • Perform the draining and flushing procedure by following the instructions from the manufacturer of the heater.
  • Close the purge port valves by twisting the T-shape handles.
  • Disconnect and then remove the hosing lines from the water valves.
  • Replace the caps of the purge port valves.
  • Re-start your water heater.
  • Turn on the sink’s hot water tap in order to allow any air stuck inside to pass through.

Once again, while you can safely clean/maintain your gas tankless water heater on your own, it is highly recommended that you hire someone to install it.
Of course, installing it on your own can save you up to $3,500. However, if you do something wrong, you may be in for a more expensive and severe problem. As mentioned above, unless you know what to do, refer to a professional!

Frequently Asked Questions about Gas Tankless Water Heaters

  1. How much money can I save with a gas tankless water heater?
    Depending on the model of your heater, you can save between 5% and 69% off your water heating bill. Moreover, using certain select models may also help you save up to $300 on your next tax bill.
    In short, given that such a unit heats water only when you are actively using it, you will definitely save a lot of money – up to $200 per year, depending on demand and model.
  2. Do high altitudes affect my gas tankless water heater?
    It is known that gas units start to lose efficiency the higher they are placed. For example, for any altitude over 4000 feet, a gas unit will lose roughly 4% of its BTU for every 1,000 feet above.
  3. Will one gas tankless water heater be enough to heat my entire home?
    Yes, some models – especially gas ones – are powerful enough to heat the water in your entire home. While there are models suited for a single faucet and so on, you can go for a model that could handle, simultaneously, two showers and three faucets.
    However, keep in mind that you have to properly size your water heater, in order to make sure that it can meet the hot water demand. Also, check out our blog post to see how long it takes for a water heater to heat up.

Don’t forget to check out the excellent options for filtering your water!

Wrap Up

Now you know which the best gas tankless water heaters are and much more!
With the help of our gas tankless water heater reviews and additional information that we’ve provided you with, we hope that you will be able to make a smart purchase if you intend to buy a water heater in the near future.

Keep in mind to take into account all of the things we mentioned in the buying guide, as well as the pros and cons of such products. Make sure that you can deal with the costs involved by a gas tankless water heater as well.

However, even if it may seem like an expensive initial investment, remember that there are numerous people claiming that a tankless water heater has saved them money in the long run!

In case you are replacing an old water heater you may also be interested in our article about how to dispose of an old water heater.

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