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Best Outdoor Tankless Water Heater For 2023

Brandon Forder
  Dec 6, 2023 3:57 AM

It's not easy to choose which outdoor tankless water heater is ideal for your household's needs. But this manual will help you get through it by recommending some of the best brands available.

Tankless water heaters that can be installed outside are highly recommended. Installing one is less complicated and costly, they take up less room, and they don't need any special ventilation. An outdoor tankless water heater is a great investment if you're in the market for a new system.

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Last update on 2023-12-06 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API

Buying Guide

Freeze Potential

If you live in the south of the United States, for example, you'll need to know how cold it can go outside before your unit freezes.

Wrapping the external water pipes in insulation or heat tape will help avoid frozen or burst pipes.

Tankless water heaters can be installed outside, freeing up floor space in the basement or garage.

Condensing Vs. Non-Condensing

Condensing and non-condensing models are the two most common varieties of outdoor tankless water heaters.

Tankless heating and cooling systems using condensing technology are more expensive but also more energy efficient by about 10%. Condensing tankless water heaters necessitate additional piping to direct condensate (water) away from the house's base.

A condensing tankless water heater is more efficient because it recovers lost energy from the condensate in the exhaust fumes.


If you have hard water, there's one thing you need to keep in mind about maintaining an outdoor tankless water heater.

It is recommended to flush the heater with a descaling chemical once a year, or every few years (depending on the size of your household).

Portable or Fixed?

Consider if you want a portable device or one that can be permanently installed in your yard.

Typically, outdoor tankless water heaters are mobile units. One need not endure another chilly shower at the camping if they bring along a unit. It's a great product for those who want to take their families on trips. It works great for washing pets, cleaning the garage, and other chores in the backyard. These tankless water heaters only have a low GPM rating, which is a major drawback.

However, a fixed unit is an option for residences where having the heater outside the house is preferred for safety reasons. Many of these water heaters are powered by natural gas. Consumption can be minimized with these models because of their higher GPM ratings.

Electric or Gas?

Is a tankless electric water heater the best option? Perhaps a product that runs on propane or natural gas would be more to your liking. Propane has a cheaper fuel unit price than electricity, making propane-powered appliances more cost-effective over time. An initial investment in a fuel-powered product may therefore be higher.

Correct Size

You need to take two factors into consideration when choosing the right size of tankless water heater to buy. Before anything else, you need to calculate how many gallons per minute are being used by your various plumbing and electrical systems. In contrast to the 2.5 GPM available from a showerhead, a kitchen faucet may only have 1.

The typical demand for water in a single-bathroom home with three faucets operating at once is 5.5 GPM. Thus, a 5.5 GPM tankless water heater is optimal.

Second, think about how the groundwater temperature compares to your ideal temperature. Calculating the disparity between the two will tell you how much of a temperature boost your outdoor tankless heater will need to provide. If you want to take a shower at 110 degrees Fahrenheit but the water comes in at 50 degrees, you need a raise of 60 degrees.

Therefore, a 5.5 GPM outdoor tankless heater at a 60-degree rise is the best option.

Energy Efficiency

The efficiency of a water heater is expressed as an Energy Factor (EF). It's a simple approach to get a quick idea of the appliance's energy efficiency.

The tankless water heater's EF rating reflects how much hot water it can produce for one unit of fuel used.

A higher EF rating indicates greater energy efficiency for tankless water heaters. What this means is that a larger percentage of the fuel will be used to heat the water.

However, keep in mind that the tankless water heater's efficiency and savings will decline as your household's hot water consumption increase.


Can a Tankless Water Heater Go Outside?

An outdoor tankless water heater installation is possible. These water heaters can survive the elements and are simpler to set up because they don't need to be vented.

Never bring an indoor tankless water heater outside, and never bring an outdoor tankless water heater inside.

Can a Propane Tankless Water Heater Be Installed Outside?

Sure, as long as it's a tankless water heater that's installed outside. Tankless water heaters are only intended for indoor use.

Manufacturers typically produce both Natural Gas and Propane versions of their tankless water heaters to accommodate regions where Natural Gas is not readily available. In addition, it is not uncommon for the same model to be available in both indoor and outdoor configurations.

How often do you need to descale an outdoor tankless water heater?

One can descale a tankless water heater product every six to 24 months, depending on the groundwater hardness level in the house. The more hardness minerals present in your liquid, the more frequent the descaling is.

As such, if one lives in a location where groundwater hardness levels reach 180 mg/L (equal to 180 ppm or 10.5 grains/gallon), one may have to descale the outdoor tankless unit as often as once every five to six months.

One may also have to descale the tankless unit once every 18 to 24 months if the groundwater hardness level is <60 PPM or <3.5 GPG.

If your groundwater is particularly hard, you may want to consider adding a whole-house water softener to reduce stress on your tankless water heater. A conditioner can also be a fantastic solution if you do not enjoy periodic softener recharge.

Do outdoor tankless water heaters run out of hot water?

An outdoor tankless unit never needs to be refilled with hot water because it is always being heated. However, it is important to select a tankless heater of the appropriate size.

For example, let us imagine you have an appliance with a maximum flow of 5 GPM and an 80-degree Fahrenheit temperature rise. If you don't need more hot water than 5 gallons per minute, then this tankless water heater will work fine for you. If you use more than that, there is a potential the appliance may not supply you with your intended temperature.


The most reliable outdoor tankless water heater can take a beating and keep on ticking without letting you down in the areas of liquid heating performance, energy efficiency, or savings. It might be a portable device you can bring to your adventures or a set appliance giving reliably hot water to your home.

If you want a safer and more efficient water heating system, it makes perfect sense to invest in a tankless water heater designed specifically for outdoor usage.

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