If you've decided to install a tankless water heater in your RV, you've already made an excellent decision. Not only will you benefit from a more cost-effective and energy-efficient appliance, but you'll also be able to enjoy near instantaneous, non-stop hot water for your dishwashing and showering needs.Athough, its true that camping and comfort will be a lot easier with a tankless water heater, finding the right RV tankless water heater for your vehicle can be a little tricky. Let's take a look at some of the main things you should consider. Quick Navigation Water Heater Power SourceElectric Tankless Water HeatersGas Tankless Water HeatersFinding the Right SizeBritish Thermal UnitAvailable Space Water Heater Power Source There are two main types of tankless water heaters: Electric and gas, and deciding which type of fuel you want to use is your first big decision. Let's take a closer look at both.Electric Tankless Water HeatersIf you're looking for an environmentally friendly heater, an electric tankless is the way to go. They're extremely energy efficient with 98 to 99% of the energy they use going into the heating of hot water, and they don't produce greenhouse gasses.Although they tend not to be able to deliver as much hot water as a gas tankless, they are still an excellent option. Regardless if you'll be using shore power, a generator, or solar panels, an electric tankless water heater will be operational. They are even relatively easy to install, and some units can even be mounted under your sink!Gas Tankless Water HeatersThe majority of RV tankless water heaters are fueled by liquid propane. However, one of the drawbacks with a gas appliance is the production of exhaust gases, and the need to exhaust these gases.Gas tankless water heaters aren't as energy efficient as electric heaters. They're also not as environmentally friendly since they release greenhouse gases into the atmosphere.There are two types of gas appliances: Non-condensing and condensing. Each uses a different method to vent the exhaust.Non-Condensing Tankless Water HeatersGas tankless water heaters that use non-condensing technology to vent the exhaust gases are not as energy efficient as condensing units. Non-condensing heaters typically reach mid-80% efficiency ratings, which means they not only produce more harmful exhaust gases, but they also use more energy, making them more expensive to operate.As a general rule, you can expect to spend less when purchasing a non-condensing tankless, however, in the long run you'll spend more because they are not as energy efficient.Condensing Tankless Water HeatersA condensing tankless water heater takes advantage of the hot exhaust. Instead of venting it away from the appliance it uses the exhaust to heat more water.Venting is still required and greenhouse gases are still produced, but a condensing tankless is far more energy efficient, and they frequently reach mid-90% efficiency ratings. You can expect your upfront cost to be higher with a condensing tankless, however, in the long run, you'll save money. Finding the Right Size The thought of having an endless stream of hot water may sound wonderful, but that's only possible if you properly size your tankless water heater. If you're replacing a 6 to 10-gallon tank you know first hand just how fast you can empty a tank of hot water. Even though a tankless water heater will instantly heat the water, if your heater is undersized it won't be able to keep up and you'll find your water lukewarm at best.A tank water heater measures it's capacity by the size of its tank. In other words, a 10-gallon tank has a capacity of 10-gallons. But a tankless water heater measures its capacity in terms of flow rate.Flow rate is the amount of hot water the heater can heat each minute. When you see the term gallons per minute or GPM, this is referring to the flow rate.The other important factor to consider is the temperature rise. If you want your shower to be 105°F and your incoming cold water is 55°F, your tankless water heater will need to increase the temperature of the water by 50°.So, if your shower has a flow rate of 2 GPM and your temperature rise is 50°, you'll need to purchase a tankless that can deliver, at minimum, a flow rate of 2 GPM with a temperature rise of 50°. Keep in mind that incoming water temperatures vary from area to area, and season to season.This is an extreme example, since you're obviously not going to purchase a tankless to meet the exact critera of your shower demands, but it does illustrate how to factor your needs.There's plenty of great tankless appliances on the market today, one we recommend is the Precision Temp RV-550 Tankless Water Heater. It's designed to be a direct replacement for a 6 or 10-gallon tank, and it's relatively easy to install. Precision Temp RV-550 Learn More British Thermal Unit Another important factor to consider when purchasing a gas tankless water heater is BTU. BTU refers to the British Thermal Unit, and it defines the heating capacity of an appliance.Comparing BTU ratings can be extremely helpful when shopping for a gas tankless. Purchasing a unit with a higher BTU rating means your tankless water heater will have more power to heat the water than models with lower ratings.The majority of RV tankless heaters have a BTU rating between 30,000 to 50,000. The Precision Temp RV-550 has a BTU rating of 55,000 BTU. Available Space Don't assume that all water heaters are the same size. It's great when you can pull your old tank water heater from the side wall and slip your shiny new tankless snuggly in place. But, unfortunately, that's not always the case.Always compare the new heaters measurements with the available space on your RV. If you need to do some cutting on the side wall to accommodate a larger heater you might want to hire a professional to do the work for you. But, in most cases, with a few adjustments, your RV will be able to handle a tankless water heater.