Tankless Water Heater Selection Guide

Tankless water heaters have become very popular in recent years due to their low cost, ease of use, and energy saving design. But with so many different types & models available, for first- time buyers deciding which one is best for them can be confusing. We’ve prepared this guide with first-time buyers in mind to help you choose the right tankless water heater for you!

Introduction to Tankless Water Heaters

Tankless water heater technology has been available for many decades. As the focus on energy efficiency becomes more important, many homeowners have exchanged their old inefficient hot water tank with a tankless model. But tankless water heaters aren’t just for home use, they are now used in cabins, RV’s, boats, construction sites, and even while camping as they are convenient, lightweight, require less space, and use less energy vs a conventional tank heater.

The major difference between a conventional tank & tankless water heater are:

A conventional hot water tank uses energy (gas or electricity) to heat a large volume of water stored in the tank to have ready for use at all times, regardless of whether you need it or not. Although the tank is insulated, it still loses heat over time and will use energy to keep the water heated to the desired temperature.
A tankless water heater is ‘on demand’. When you aren’t using hot water, the tank sits idle using zero or almost no energy (depending on the model). When you turn on your shower or open the hot water faucet, the system detects the water flow and only then uses energy to heat the water immediately to the desired temperature. When you’re finished and turn off the hot water tap, the tankless heater shuts down and waits for the next time you need hot water.

Gas vs Electric Models

Almost all tankless water heaters operate using Propane gas (LPG), with some larger models designed to work with Natural Gas (NG) or electricity. The latter are typically used for larger homes and where Natural Gas & grid electric services are available.

The Cabin Depot™ specializes in off-grid living solutions. As such, we offer primarily Propane Gas (LPG) models as 20lb, 30lb, and 100lb tank options are readily available and portable.

We do offer a variety of larger whole-home electric and Natural Gas (NG) models, but neither are suitable for off-grid applications and are reserved for grid-tied applications only:

Electric models all require 220-240vAC and typically 1-3 x 50A breakers to operate. Generally speaking, the larger the family and the more hot water taps used at one time, the larger the electrical requirement. You will need dedicated wiring to your breaker panel, and an electrician required to install.
Natural Gas (NG) models are a good alternative for larger homes where that service is available.

While the actual operation of gas & electric tankless heaters are very similar, we will only reference gas models for the remainder of this guide.

How do Tankless Water Heaters Work?

Tankless water heaters have a built-in sensor that detects water flow. When sufficient water flow is detected (i.e. you turn on the shower or hot water faucet), the unit will ignite the LPG or NG gas burner. The burner flame heats the cold water which is flowing through the heat exchanger above it. The heat exchanger looks similar to a car radiator, with a winding pipe / coil. By the time the water exits the heat exchanger, the water is hot.

Adjusting the Hot Water Temperature

There are 2 ways that tankless heaters control the water temperature: water flow rate, and flame size.

For manual gas models, you’d adjust the water flow, or the flame size, to adjust the water temperature by the control knobs located on the front of the heater. The slower the water flows through the unit, and/or the higher the flame, the hotter the water. Conversely, the faster the water flow, and/or lower the flame, the cooler the water exiting the unit will be. Manual models like this are usually outdoor / portable. Many customers use these for their seasonal use cabins and plumb them inside. While inexpensive and convenient, customers find it very difficult to regulate the water temperature when trying to mix hot + cold water.

*Note: For optimal energy conservation, if you don’t require high water pressure, you can heat the water to your desired temperature and use less gas by slowing down the water flow.

Above: Manual gas & water flow adjustment on outdoor / portable heaters

For automatic gas models, you’d simply select your desired water temperature using the LED screen pad and the unit will automatically adjust the flame based on the incoming water temperature. Most indoor tankless heaters use this technology today, and they are ideal for situations where you may be mixing hot + cold water, or are using a water source that has wide temperature swings (i.e. lakes, streams, rivers, or rainwater collection systems).

What Size do I Need? LPM/GPM Explained

All tankless water heaters are rated as LPM (Litres Per Minute) or GPM (Gallons Per Minute). But interestingly enough, almost all heaters have their size in Litres built into their model number.

This is because most countries are now using the metric system, and the vast majority of tankless heaters are built in China. So, when you see the Marey 5L, Camplux 5L, or Eccotemp L5 for example, these are all 5 Litre per minute heaters (also sometimes advertised as 1.6 Gallon per minute). But what the heck does that even mean?

The 5L models are the smallest available, so we’ll use them for this explanation: Simply put, the larger the LPM or GPM advertised, the higher the btu capacity (heating capacity). Most 5L models are rated for 37,500btu. So, when you see 5L or L5 in the model number, it means it will sufficiently heat 5 Litres (1.5 Gallons) of water consistently when passing through it. However, there are many factors & limitations which may impact the ability of the heater to provide “hot” water. The incoming water temperature is the deciding factor as well as the air temperature when used. If you have very cold incoming water, a 5L unit will not give you hot water. You’ll be lucky to get lukewarm water at best. So, with that in mind, our recommendations are:

If using a tankless water heater in the southern US states (excluding high-elevations), the 5L shower kit models should satisfy most hot water requirements regardless of the season or water source. If the heater is being used as a permanent installation or for multiple faucets, the larger 8L, 10L, 12L, or 16L models are recommended with the final size depending on your specific application.

If using a tankless water heater in the northern US states or Canada, the 5L shower kit models will perform well in late spring / summer / early fall. If using lake, stream, river, or rainwater collection systems during early spring or late fall months in particular, you will need at least the 8L or 10L models to provide sufficient water heating for outdoor showers. And for year-round indoor applications & multiple faucets being used at one time, the 10L, 12L, or larger EL22i & equivalent may be needed.

Indoor vs Outdoor Tankless Water Heaters – What’s The Difference?

In North America, there are 2 common types of tankless water heater on the market: Outdoor (also known as Outdoor - Portable) and Indoor. The major differences for LPG models are outlined below:

Outdoor Tankless Heaters:

Are lightweight with models starting at just 13lbs, easy to transport, connect, and use.
Does not require venting
Uses no power when idle.
Use batteries (typically 2 x D or 4 x AA) for the ignition. *Note: These batteries will last 2 years on average depending on how often the heater is used, and should be removed when the unit is put into storage.
Cannot be used during winter months in northern climates. Allowing water to freeze inside the unit will cause permanent damage!
Water temperature selection is manual typically using 2 knobs which adjust the water & gas flow. Incoming cold water temperature changes will require adjustments to these settings to reach the desired temperature.
Are meant to be installed & used outdoors only:

In a camping situation, they are temporarily mounted to be used for showers & hot water for washing hands & washing dishes, and taken down after use. Examples of these kits would be the Camplux 5L, 8L, 10L, Eccotemp L5, and Marey L5 portable and 10L bundle. These kits normally include the tankless heater, propane hose with regulator for connection to a 20lb or 30lb propane tank, a shower head with hose & on/off switch, and adapters that give the option to connect the unit directly to a water line, or via a garden hose.
In a seasonal use cabin situation, some customers mount them outside of the building with the water lines plumbed into the cabin. They can be used to provide hot water for dishes, washing hands, bathing, or showers (although showering may be difficult, see our FAQ section later in this guide for details). They are put up in the spring once freezing temperatures are no longer present, and taken down in the fall, drained, and stored for the next season. These heaters are typically larger in size and do not come with a shower head. Some models may come with the propane hose & regulator for connection to a 20lb or 30lb tank. Examples of these kits would be Eccotemp L10, Marey 5L, 10L, 16L. Camplux also offer models that can be used for this application.

A brief note on installing outdoor / portable heaters inside a building: Many countries with warmer year-round temperature allow the installation of these types of heaters inside using standard venting, but trying to install and use these heaters year-round in colder climates will result in the unit freezing and suffering permanent damage. Indoor models have a powered vent with backflow preventer built in to keep the cold air from entering and freezing the unit. Customers attempting to use these heaters for an indoor installation will find that the cost of the proper venting and accessories will often be the same or even more than the cost of a proper indoor tankless heater. Also, very few of these heaters are certified for indoor use as most jurisdictions now require powered venting to ensure your safety and prevent carbon monoxide poisoning. You will need to check your local building codes before attempting to install.

Indoor Tankless Heaters:

Are larger in size and weight, starting at 33lbs.
Meant for permanent indoor installation and do not come standard with any propane lines or regulator. Propane & water connections will require additional parts (specifically a propane regulator & lines). DIY installations are common and not difficult, but depending on the model, your specific application, and geographical location, you may require additional installation accessories to meet local or national building codes.

Requires venting – smaller indoor tankless heaters include a stainless steel horizontal vent kit and wall thimble which ship inside the tankless water heater box. Larger tankless heaters do not come with a vent kit, and when purchased as a bundle they will be shipped in 2 separate boxes.
Are typically installed on an exterior wall and use a horizontal vent kit. Vertical vent kits are available but are made to exhaust through the roof which makes their cost much higher.
Requires 110-120vAC via a standard plug which powers the LED screen, exhaust motor, and ignition circuit. These units are typically rated for just 7 to 30 watts when idle (for powering the LED screen) and around 120 watts when operating (for powering the ignition circuit and exhaust fan) which still makes them an idea choice for off-grid applications using solar power + inverter. They can also be unplugged when not in use.
Can be used year-round provided the indoor space is heated. Most vent kits come with a ‘backflow preventer’ which is a flap inside the venting that closes after use to keep the cold air from entering the unit. However, it’s important to note that in more northern climates where extreme cold temperatures are present, you may need to have the room heated to a higher temperature or add additional exhaust venting to prevent freezing.
Are fully automatic, meaning once you set the water temperature, the unit will adjust the flame size to keep the water temperature at the pre-set level regardless of the incoming water temperature or pressure.
The most common heaters for seasonal use cabins & smaller off-grid homes are the Camplux 12L and Eccotemp i12. The most common for full-time occupied larger homes are the Eccotemp EL22i, 20HI, and 45HI and Marey 16L ETL.

Efficiency Ratings & Rebate Programs

Some manufacturers boast high efficiency ratings and use them to justify substantially higher retail prices. In some US States & Canadian Provinces, energy efficiency programs are available that provide rebates of a few hundred dollars for installing indoor tankless water heaters that achieve an efficiency rating of ‘xx’. Unfortunately, these heaters cost many hundreds or even thousands of dollars more vs a heater that may be slightly less efficient, and usually as part of the qualifications for the rebate the heater must be installed professionally. It is our opinion that while efficiency ratings are important, rarely does paying substantially more $ for a home tankless water heater make economic sense. And here’s why:

Generally speaking, if you’re paying $1,000 for an indoor whole-home tankless water heater, but the unit that qualifies for the rebate costs $2,500 you would need to save $1,500 in energy costs just to break even. It’s not uncommon for a standard indoor LPG tankless water heater paired with a 100lb tank of propane to last more than a year when being used by a couple for bathing, showers, clothes & dish washing. Assuming a $400 rebate, the difference in price would still take more than 20 years to break even. Will you still be using that same tankless water heater in 20 years? Probably not. But if you’re using a lot of hot water every day and have a large family, then paying more money for a higher efficiency unit may make sense.

Frequently Asked Questions

Q: I have a gravity feed water system. Will that work with a tankless water heater?

Most tankless water heaters require a minimum of 22psi of water for the ignition circuit to activate, and 40psi+ for proper continuous operation. In our experience, and as verified by many of our customers using gravity feed systems, the pressure just isn’t enough for the unit to operate properly. There are of course exceptions, but most customers will need to add a small 12v or 24v diaphragm pump. These pumps are low power and on demand, low cost, and very common for off-grid water requirements.

Q: The installation manual for my water heater plumbing connections show several valves, pressure relieve valves, and other accessories needed to install? Are they actually needed?

Manufacturers of tankless water heaters are shipping units all over the world and must adhere to best practices and code requirements. Your heater does not need any of these items to function, you need only to connect the cold water input, and hot water output, and the heater will operate as intended. These parts have no effect on the operation of your unit and in most seasonal or cabin installation situations customers choose not to use them. However, if you are installing a tankless heater in your home to code, depending on your location these parts are usually required to satisfy inspectors.

Q: I see some heaters are CSA certified and some aren’t. What does that mean?

CSA (also known as the Canadian Standards Association) is a company recognized in the US, Canada, and around the world that tests products and provides their certification which is often required by insurance companies and been adopted as the standard used for many building and installation codes. Companies may choose to seek certification; in which case they submit their product to CSA for testing and pay a fee. Specific to tankless water heaters, they will test things like the gas connections, water connections, operating limitations in various environments, risk of fire, and subject the unit to other tests to ensure safe operation. Because of the high cost to obtain CSA certification, many manufacturers choose only to certify some models. This does not mean the products that don’t carry the CSA sticker aren’t safe, in many cases the design of the unit and internal parts used are identical. If you are installing a tankless water heater, and want to ensure you’re meeting local building codes and insurance requirements, you will want to have a heater that is CSA certified.

Q: Why can’t I use the cheaper outdoor tankless models inside? Many even have a spot to attach a vent on top?

All gas tankless water heaters will consume oxygen & produce carbon monoxide when operating. In Canada and several US States now, laws have been created to protect consumers and reduce the risk of accidental carbon monoxide poisoning. Outdoor tankless heaters do not have the option of a powered vent, which is required to ensure the exhaust gasses are evacuated from the building properly. When you use a heater designed for outdoor use inside, even with a vent, you are still releasing some amount of carbon monoxide inside the building. In colder climates, using this style of heater even with a vent will still freeze and cause permanent damage. And finally – the cost of purchasing an outdoor heater and adding the vent is often more than buying an indoor heater which comes with the proper vent kit.

Q: How long will a 20lb propane tank last?

We get this question a lot, and the answer is – it depends! Most customers with off-grid seasonal use cabins using their heater on weekends mostly will get an entire season of dish washing and showers out of a 20lb tank. If you have an off-grid home and are using the heater every day, your consumption will be much higher. Of course, there are other factors to consider, such as the btu rating of the heater, your temperature setting, and the temperature of the incoming water.

Q: Can I use these heaters for my in-floor heating?

The short answer is = no. The reason is that most of these heaters have safety features that prevent accidental scalding and fires, so they have a 20 minute timer. After 20 minutes of continuous operation, the heater will shut off automatically. You need to turn off your water tap, and turn it back on again for the unit to reset. So for that reason alone, they can’t be used for in-floor heating systems.

Troubleshooting Tips & Tricks

The first thing to note is that if you’re having problems with your new tankless water heater installation, that 99% of problems are caused by insufficient water pressure or flow! It’s that simple.

My heater won’t start / ignite, or goes out shortly after I turn on my water tap / shower:

If you turn on your tap, and hear a clicking sound coming from the heater, skip this section & move on to ‘Section #2 Gas Supply’. If you turn on your tap and don’t hear a clicking sound coming from the heater, use the steps below first to troubleshoot. We’ve listed them in order of what to check first…

Section #1: Water Pressure / Flow

For outdoor models, did you put new batteries in the heater, and install them properly with the (+) and (-) facing the correct direction? For indoor models, did you plug the unit in? These may seem like silly questions, but you’d be surprised how many people don’t think of this… But you did – so let’s move on…
Are you using a water pump that is able to provide the required water pressure? If you have a deep well pump and pressure tank, you certainly should. And all of our diaphragm pumps offered will supply adequate operating pressure. If you’re using a gravity feed system, you probably need to add a pump but there’s other thigs you can try first (see below). So if your pump pressure is fine, let’s move on…
If you’re using a diaphragm pump, have you properly primed it before using? If you aren’t sure, see ‘12v / 24v diaphragm pump priming tips’ below.
Are there any blockages in the water intake? If drawing from a lake or stream, sediment and debris can accumulate in the filter or inlet screen of the heater. Clean the filter, and disconnect the water intake hose from the heater, underneath the heater intake line you will see a small screen, wipe that clean with a cloth and reconnect. No blockages? Let’s move on…
Do you have the water control valve opened up fully on your heater? On outdoor models, this is the knob located on the front of the unit, you will want to set it to maximum flow. For indoor models, there’s a small valve on the cold water intake, just ensure it’s opened fully. Everything is opened up? Ok, let’s move on…
So you have enough water pressure, no blockages, and water valves are opened fully. The next thing to check is your output lines. Any restriction at the tap or shower head will reduce the water flow and prevent proper operation of your heater (if you are using an outdoor heater that came with the shower head and hose, you can move on to the next section). If you installed your heater and are using it for an indoor application, ran water lines to various taps and shower/bathtub for example - almost all tap sets and shower heads come from the factory now with water flow restrictors which look like a little plastic disc with a small hole in the middle (see example below). These water fow restrictors are meant for people on city water service to prevent excess use of water & reduce consumption (and reduce your water bill). In an off-grid situation, water supply isn’t usually an issue as customers are using wells, rainwater collection, lakes, rivers, and streams for their non-potable water. And these restrictors actually work against your tankless water heater and in some cases prevent the unit from igniting as the water flow is just too low for the system to ignite. Simply unscrew the tap head or shower head, remove this ring, and reattach. You will see a significant change to your water flow and with any luck your heater will begin to work normally.

Section #2: Gas Supply

Have you connected your propane tank and opened the valve? You may think this is a stupid question as well, but some people do forget to do this…
Do you have propane in your tank? Another stupid question, of course you do…
Are you using the regulator that came with the unit (outdoor model) or have you purchased a regulator large enough for your heater (indoor model)? If your regulator is undersized, it won’t supply the correct amount of propane gas to your heater.
If you just installed a new regulator and longer propane line to your heater, it may simply need to be bled. Continue to try the heater, if you still hear a clicking sound after several attempts but it hasn’t lit, you will need to contact the manufacturer. Let them know all of the testing you’ve done up to this point, it will save a lot of time when processing a warranty claim.

12v / 24v diaphragm pump priming tips:

Most diaphragm pumps such as the SEAFLO, Shurflo, Flojet, and Eccoflo will self-prime. This means they will pull water vertically up to the pump from a distance of 6-10 feet (depending on the model).
When priming for the first time, make sure your inlet connections are tight as any air will prevent the pump from priming. Do not attach your outlet side of the pump until you’ve primed the pump, it will make the process much faster!
These pumps will push water over long distances easily. We have many customers with 100’+ runs using ½” or ¾” PEX uphill 30’ and even 50’ vertically to their cabin. However, the pumps have a built-in check valve which will fail prematurely because of the added pressure of the water being held back. For longer runs and any with vertical lifts of more than 10’, the addition of an in-line check valve or foot valve is highly recommended.

I’m mixing hot + cold water to make warm water for my indoor shower, but I can’t keep the water temperature regulated. Why?

This is a common problem, especially when using smaller diaphragm pumps with a set of taps to run a shower. Those using larger well pumps and pressure tanks won’t have this issue, but then again, you also just paid thousands of dollars to have a well drilled and invested in the required hose, wiring, well pump, submersible pump, etc. So of course, it will work…

But if you’re like most seasonal cabin users and have an $89 diaphragm pump drawing water from a lake, stream, or water collection system and are having issues with regulating your shower temperature, here’s why… Most diaphragm pumps will provide lots of pressure, but are low flow (lower LPM / GPM) and are designed to supply water to a single tap at a time. You can find these types of pumps in RV’s, boats, and they are very common nowadays in off-grid seasonal cabins.

When using outdoor / portable heaters that have been plumbed into the cabin, remember that the hot water temperature is regulated by both the flame and water flow which you set manually using the knobs on the front of your heater. When you turn on the hot water tap for the shower, and feel the water is too hot, you obviously will turn on the cold to make it warm – right? But when you do this, the water flowing through the tankless water heater slows down because the diaphragm pump isn’t able to keep up to the flow demand, and when the water flow slows down the water passing through the heater gets hotter. But it takes time for that water to reach the shower head, so thinking you’ve adjusted the taps for the perfect shower temperature you jump in, but just as you do, the ‘hotter’ hot water now reaches the shower head, and the next thing you know the water is too hot again. So you turn the cold water on even more to compensate… this process will repeat itself and you will never be able to ‘balance’ the water to the right temperature. When using an outdoor / portable heater this way, there’s only a few ways to help prevent this:

Set the water temperature on the heater to your desired showering temperature, and then just use the ‘hot’ water tap when showering. This isn’t very convenient since the water temperature will still fluctuate as the outdoor air temperature and incoming water temperature changes. So each weekend you arrive you have to reset your heater to provide the desired hot water temperature.
Install a pressure tank on your main line after the diaphragm pump. This will work for quick showers unless you install a larger tank, otherwise the flow will slowly drop until it reaches the pump pressure. So for quick showers, this is a good solution. It takes a bit of know-how to set this up as well.
Separate your hot & cold feed lines, and install a 2nd pump to service your hot water line exclusively. This will work, but after all of this time & expense, option #4 will make more sense…
If you’re showering this often and want to have a shower the temperature you want, buy a proper indoor tankless water heater! It will automatically adjust your water temperature for you and maintain it. The most common way to shower when using an indoor heater is to remember what temperature you like you water. I like my showers at 100F, so I just select 100F and turn on the hot water and jump in. I’m a happy camper… my wife prefers her shower & bath water the temperature of molten lava, so she will turn it up to a much higher setting, but again only uses the hot water tap. If you still want to mix hot + cold water to shower, you can, but the flow will be exactly the same, and you’ll just be burning more propane to heat up and then cool off your shower water.