Hot water is a basic requirement, but the range of tank-based and tankless systems now available can make choosing the right water heater a real challenge. Though traditional water heater tanks remain popular, modern tankless models could offer a number of advantages. Installation costs are modest, and the machines are highly energy efficient, so you’ll save money upfront and in the long run. What’s more, a tankless model can often be installed in places where a tank isn’t practical. There are even models designed for RVing and camping.
A tankless water heater supplies hot water “on demand,” meaning that it heats the water you need when you need it. This way, there’s no danger of the tank running out and no energy wasted keeping water warm all day and night. Gas-fired models are particularly efficient. For those living in areas where natural gas isn’t available, propane offers a flexible and affordable alternative. Use this guide to learn what to look for when shopping for the best propane tankless hot water heater, and find out why the models discussed here are considered among the best propane tankless water heaters on the market.
- BEST OVERALL: Rheem 9.5 GPM Propane Indoor Tankless Water Heater
- RUNNER-UP: Rinnai 7.5 GPM Propane Interior Tankless Water Heater
- BEST BANG FOR THE BUCK: Rheem 7.0 GPM Propane Indoor Tankless Water Heater
- BEST FOR SMALL HOME: Rinnai Indoor Tankless Water Heater Propane 6.3 GPM
- BEST FOR LARGE HOME: Rheem Performance Platinum 11 GPM Water Heater
- BEST FOR CAMPING: Eccotemp L5 1.5 GPM Outdoor Tankless Water Heater
- BEST FOR RV: Camplux Pro 1.58 GPM Tankless Propane Water Heater
What to Consider When Choosing the Best Propane Tankless Water Heater
Propane tankless water heaters offer hot-water solutions for numerous situations. These versatile units can supply an entire home or be a cost-effective solution for a guest accommodation. There are even models you can strap to a tree when camping. To choose wisely, it’s best to understand the technical aspects detailed below.
Indoor vs. Outdoor
Propane tankless water heaters are available as indoor or outdoor models. Indoor models are compact enough to fit in much smaller spaces than a typical water tank, but consideration must be paid to obtaining the gas supply from outside, where it is almost invariably stored. Additionally, burning propane produces carbon dioxide (CO2), which is toxic in confined spaces, so venting is necessary. In most cases this means making a hole through an external wall or roof.
The installation of an outdoor model can be much simpler. It needs a cold-water supply, and, of course, the gas needs to be hooked up, but then the only pipe required to enter the house is the one that provides the hot water. While some need electricity hooked up, portable models generally run on batteries.
Outdoor units have their limitations, however. A propane tankless water heater will work effectively in temperatures below zero, but the unit will need protection from rain, snow, and high winds. Similarly, those models designed for camping or other off-grid use shouldn’t be left out in bad weather.
Flow Rate (GPM)
Flow rate for a tankless water heater refers to how much hot water the unit delivers, so it’s perhaps the single most important factor in choosing the best model for your needs. It is typically measured in gallons per minute (GPM), although some European models are measured in liters per minute (l/min), and there are 3.78 liters to the gallon.
The GPM rating for a propane tankless water heater is an indication of the amount of hot water the unit can supply. Accuracy is limited because it depends on the temperature of the water coming in, but general assumptions can be made. A standard faucet, for instance, requires a supply of around 1 GPM, while a shower needs 2 to 3 GPM.
Added together, everything in a house that consumes hot water at the same time theoretically gives the GPM needed for the household. However, it’s unlikely that the faucets, showers, tubs, and washing machines would be used together at once. In real terms, a unit in the region of 5 GPM is usually adequate for a small home; 7 to 10 GPM would provide for a medium to large residence. Those who need greater capacity can investigate twin and multiple heater systems.
It’s important to understand that the colder the mains supply, the harder the heater must work, and this will result in a drop in GPM. The difference in flow rate between a heater fitted in the northern U.S. compared to warmer southern states can be several GPM. Manufacturers frequently provide comparison figures to help the buying decision.
Power Output (BTU)
Heating power is rated in BTUs (British Thermal Units). Technically, it is the amount of energy needed to raise 1 pound of water by 1 degree Fahrenheit. In practical terms, the BTU rating is given as a per-hour figure to indicate how much heat a tankless water heater can consistently provide. This is crucial to consider, since if insufficient heat is generated, the water passing through the system may not get hot enough.
Math formulas to calculate BTU requirements exist, but manufacturers usually provide accurate guidance. Some offer online calculators. It’s also interesting to look at minimum BTU figures, which tell you that the heater can run efficiently at low demand and doesn’t burn fuel unnecessarily. Typically a 9 or 10 GPM propane tankless water heater might deliver anything from 25,000 to 200,000 BTUs of heat, which many consider sufficient for a 3-bathroom home.
A high-efficiency water heater saves money by converting fuel to heat energy with minimal loss. Some of the best propane tankless water heaters have claimed ratings of 99 percent, which is as good as it gets; 100 percent efficiency is impossible, as some energy is always lost.
However, manufacturers have historically used different ways to measure efficiency, and this has led to confusion. In 2017, the U.S. Department of Energy (DOE) established an independent measurement standard called the Uniform Energy Factor (UEF). This allows potential buyers to make accurate comparisons. Figures are given as a fraction of 1. Among the Top Picks in this guide, these range from a low of 0.8 to a high of 0.93.
Condensing vs. Noncondensing
Hot-water vapor—steam—is an unavoidable byproduct of the heating process. When steam reaches a cooler area of the heater, it normally condenses, turning into water droplets. There are two problems associated with this. First is the heat loss that comes with steam escaping. Second is that the water eventually starts to cause corrosion.
Noncondensing models vent the steam to the outside air. Steam can be as hot as 300 degrees Fahrenheit, so care must be taken with how this is done. The process also wastes a lot of energy. Condensing models recirculate the steam, harvesting the energy to help heat the water. Though eventually vented to minimize corrosion, by the time this happens, the temperature will have dropped to about 100 degrees Fahrenheit. In other words, a condensing propane tankless water heater can utilize 200 degrees Fahrenheit of heat that would otherwise have been wasted.
The downside is that condensing models are considerably more expensive. However, with heater lifespans of 10 to 20 years, there’s plenty of time to recoup the difference.
Venting is necessary for two reasons: to bring air in for the combustion process and to get rid of dangerous carbon dioxide after. It’s common to have separate ducts for each, but some heaters use a concentric vent—effectively, one pipe inside another. Low-cost PVC is often used, though concentric models are more expensive. Stainless steel is another option, but, again, more costly. It’s common for venting to be from the top of the unit, but side-venting models also exist.
It’s important to check the venting requirements of each model being considered. It will have an impact on installation, and some models require a specific ventilation kit—which is frequently not included in the purchase price.
Size and Weight
Propane tankless water heaters are wall mounted and generally less than 15 inches deep. This allows them to save a great deal of space compared to traditional floor-standing boilers. Nevertheless, it is worthwhile to check physical dimensions when planning the installation. Portable models are considerably more compact. Weight will be a factor, but most are less than the 20-pound propane tank used to fire them.
Some propane tankless water heaters have nothing more than basic dials for water flow and temperature and an LED to indicate whether it is operating or not. However, a number of more advanced functions are available:
- Different settings for summer and winter take into account ambient temperature. These are particularly valuable on outdoor models and can offer considerable fuel savings.
- Digital displays give precise readings of the water temperature being provided and offer more precise control. WiFi-enabled heaters can even be controlled via an app.
- Many portable models come with the necessary gas regulator to fit a standard 20-pound propane bottle, and some have a showerhead included.
Devices may be UL or CSA certified, meaning they have been independently tested and meet a range of international safety standards.
Installation and Maintenance
Whichever propane tankless water heater is chosen, installation requires a range of skills and tools likely to include both plumbing and minor building works. If you want to do DIY installation but don’t already own the tools, purchasing them can add considerable cost. Additionally, several manufacturers strongly recommend that a qualified professional undertakes installation.
If a permanent propane tank is to be part of the installation, there are specific regulations that must be adhered to. Experienced DIY enthusiasts might be able to undertake the task themselves, but in many cases, hiring a contractor might be a better idea.
These are very durable units, but the life of even the best propane tankless water heater will be extended with occasional maintenance.
- Those who live in hard-water areas should consider installing a filter in the cold-water supply to reduce calcium buildup.
- An annual flush, using a circulating pump and white vinegar, provides effective demineralization, preventing the buildup of chemicals that will impede performance.
- At the time of the annual flush, it’s wise to check fittings for signs of corrosion and replacing what might prove necessary.
Our Top Picks
The sections above provide a fairly comprehensive overview of the factors and features to keep in mind when shopping for the best propane tankless water heater. Now review these top picks from known manufacturers to home in on the model most appropriate for your particular needs.
For efficiency, reliability, versatility, and a host of standout features, this Rheem tankless water heater is a solid choice. Designed for indoor use, it’s a compact unit rated at 9.5 GPM and a maximum 199,000 BTU. It is sufficient to run four showers (or equivalent) simultaneously. It is DOE Energy Star certified with a market-leading UEF of up to 0.93. A water-saving feature can reduce consumption by up to 1,100 gallons per year.
Precise digital controls make setting the preferred temperature simple. Built-in sensors alert you when maintenance is required. Compatibility with PVC venting pipe reduces installation costs, and venting distance of up to 150 feet allows great freedom in terms of where it can be fitted.
With its flow rate of 7.5 GPM, it might be easy to underestimate this Rinnai indoor propane tankless water heater. Yet it offers a money-saving alternative to high output systems and, with up to 180,000 BTU, it can run two or three showers consecutively, even in regions with cooler groundwater temperature. The unit’s UEF is 0.81.
Recirculation technology reduces hot-water delay. Digital control with Wi-Fi compatibility allows precise temperature setting. While faults are rare, this model will provide extensive diagnostic error codes should that happen.
The unit can be fitted with standard or concentric venting; horizontal venting is available at an extra cost. Both isolation and pressure-relief valves are included, which help make annual maintenance flushing much easier.
Those looking for a competitively priced indoor propane tankless water heater might consider this Rheem. With a maximum output of 7.0 GPM and 160,000 BTU, this model, with a UEF of 0.82, can supply the needs of a 1- or 2-bathroom home.
Despite the comparatively low cost, some impressive features are included. A digital thermostat offers accurate temperature control, and it can be installed remote from the unit for added convenience. A hot start program reduces water temperature fluctuations that can be caused by stop/start use. While this model does require stainless steel venting, which will add to the cost, it remains an affordable and energy-efficient option for modest residences or guesthouses.
With a rating of 6.3 GPM and 150,000 BTU, the indoor Rennai V65 is designed for smaller homes. That said, UEF is high at 0.92, so it provides outstanding energy efficiency.
While the Rennai V65 lacks Wi-Fi compatibility and the app of some of its more powerful siblings, it has a clear digital readout for precise control. The manufacturer touts the model’s easy install yet nonetheless recommends hiring a pro for the job.
Rheem produces a number of high-quality propane tankless water heaters, and the indoor Performance Platinum tops their range. It runs at up to 11 GPM and 199,000 BTU, with a UEF of 0.93. It is designed to provide for the needs of a 4-bathroom home.
Recycling technology reduces the time it takes for hot water to go from the unit to the faucet or shower. The system, which is both UL and CSA certified, can be programmed to suit homeowner usage patterns, has a digital panel for precise control, and is capable of detecting gas or water leaks. Compatibility with PVC venting reduces installation costs, and the Energy Star-certified unit can save thousands of gallons of waste water annually.
The Eccotemp L5 is designed for those who love the great outdoors but don’t want to put up with cold showers. It produces 1.5 GPM at up to 37,500 BTU and has a UEF of 0.8. It weighs just 11 pounds, so it’s easy to carry anywhere.
While figures are modest compared to indoor models, depending on conditions, the Eccotemp L5 can produce hot water up to 140 degrees Fahrenheit. A low-pressure supply from a standard garden hose is all that’s needed (though a 12-volt pump will improve performance). There’s no need to worry about electricity, as ignition is provided by two D-cell batteries.
The specifications of the Camplux Pro portable outdoor water heater are impressive. While it weighs just 14 pounds, it can deliver up to 1.58 GPM and 41,000 BTU. It will work with water pressure from 3 to 110 psi (household water is generally between 45 and 70 psi), so it’s ideal for remote locations where pressure is often low. Two D-cell batteries provide ignition. A showerhead and a convenient hanging bracket for the side of your RV are included.
A very safe unit, it will sense if water pressure is beyond normal range or if the flame has failed, and it will shut off automatically if overheating. There’s a drain plug for residual water to prevent damage from freezing.
FAQs About Propane Tankless Water Heater
Even after reading this propane tankless water heater primer, you may still want more information about the technical aspects of these devices. Here, some of the most frequently asked questions are addressed.
Q. How does a tankless water heater work?
Turning on the hot-water faucet trips a flow sensor, which turns on the propane burners, which heat water “on demand.” No water sits around going cold in a big tank. As soon as the water flow stops, the burners turn themselves off so no energy is wasted.
Q. How big a propane tank do I need for a tankless water heater?
It depends on the demands of the heater. Those for camping and small homes might run for several weeks off a standard 20-pound bottle. Bigger propane containers are available for large-capacity heaters, or a permanent tank might be warranted.
Q. Can a tankless water heater work for the whole house?
Absolutely. Models are available to supply hot water to all sizes of homes. Consideration should also be given to the propane tank setup, as mentioned in the question above.
Q. How do you flush a condensing gas tankless water heater?
To perform this annual maintenance function, propane and water supplies must be shut off and electricity disconnected or battery removed. White vinegar is typically used to flush the system and remove sediment. Manufacturers often provide complete instructions, but if you’re unsure about proceeding, hiring a professional to do the job once a year should not be a huge expense.
Q. How is the gas pressure on a tankless water heater checked?
Generally speaking, there shouldn’t be any need. On these devices, a regulator fitted to the propane tank controls gas pressure, and the correct type should have been fitted during installation. Lack of hot water is usually due to either a near-empty propane tank or water pressure being too high. If you do need to check gas pressure, you’ll need a specialist manometer. In that case, it might be wise to have your tankless water heater checked by a plumbing professional.