The New Kid on the Block: RV Tankless Water Heaters

The typical American shower guzzles about 18 gallons of water at a rate of 2.1 gpm (gallons per minute). It’s warm, steamy, refreshing, exfoliating.

If you replicated that same shower in the typical RV, you’d run out of water in about 2 minutes and 52 seconds. Barely enough time to work up a lather.

For decades, the standard RV water heater* has used a 6-gallon tank. Larger RVs may use a 10-gallon tank.

Compare that to a residential water heater, which is at least 30-50 gallons!

RVers have adapted by taking Navy-style showers, using dry shampoo, and showering only when the neighbors start burning incense and wearing gas masks as you walk by.

But there’s an uppity piece of technology that may render obsolete all those water-saving hacks. It’s called a tankless RV water heater, also known as an on-demand water heater.*

Let’s chat pros and cons of conventional tank water heaters versus on-demand tankless water heaters. Is the latter worth the extra cost? Is the former big enough for a weeklong vacation?

*That’s “water heater,” not “hot water heater” to you Neanderthals! But irregardless of what one you use, I hope your able to except that its the proper enunciation.

Meet the Family: RV Water Heaters

Intro to Conventional RV Water Heaters

A conventional RV water heater is a rather simple affair. It’s a tank with a heating element and some fancy-schmancy electronic controls, wrapped in insulation.

Premium models may have other features. Electronic ignition reduces the consumption of propane, for instance.

You’ll also see anode rods in older units with steel tanks. The anode is a sacrificial component; the anode corrodes, not the tank wall! Modern water heaters have aluminum-clad tanks, which don’t need an anode rod.

All RV water heaters need to be winterized by flushing water out of the system. Since water expands when it freezes, ice can rupture pipelines and damage sensitive components.

Most conventional water heaters can be operated using either propane gas or 120V electric power. Almost all water heaters must be connected to 12V power for the electronic controls to work.

Common tank sizes are:

  • 4-gallon
  • 6-gallon
  • 9-gallon
  • 10-gallon
  • 12-gallon
  • 20-gallon

With 6-gallon and 10-gallon being the most common in everything except the largest 5th wheels and motorhomes.

Water heaters will deliver a line temperature of around 95 to 125 degrees Fahrenheit (you choose). Some can go as high as 140 degrees Fahrenheit. Most will automatically shut off (for safety reasons) if the temperature exceeds 140 to 150 degrees.

Generally, 100-105 degrees is considered a safe bathing temperature. At 120 degrees, skin will scald after 5 minutes of continuous contact. At 127 degrees and above, you have less than a minute. Ouch, ouch!

Temperature (deg. F)Time To Scalding
1551 sec
1482 sec
1405 sec
13315 sec
1271 min
1243 min
1205 min

When evaluating the heating capacity of a water heater, best to look at the BTUs. The bigger, the better.

A conventional water heater is typically rated around 10,000-12,000 BTUs. That’s not enough heating power to warm water continuously, so conventional water heaters often have a stated “recovery time” – that is, how long it takes to reheat a full tank to operating temperature.

Recovery rates are normally stated in gallons per hour (GPH). Gas/electric water heaters have two recovery ratings: one for the LP-mode recovery rate (usually 7.4-13.5 GPH), and a smaller one for the electric-mode recovery rate (usually 5.2-6.5 GPH). If modes are combined, the recovery rate can exceed 16 GPH!

In practice, this means you normally have to wait at least 20 minutes to get hot-ish water out of a drained water heater tank.

Intro to Tankless RV Water Heaters

Now that you know about conventional RV water heaters, you see their shortcomings.

  • Conventional water heaters don’t warm water quickly.
  • Many don’t heat water consistently either!
  • Gas pilot light models can waste a lot of propane.
  • You lose a lot of power through wasted standby heat.

Enter the wonderful world of tankless RV water heaters. 

Tankless water heaters, aka on-demand water heaters, don’t have … a tank! Whodathunk?!

Rather than slowly heating a large volume of water inside a tank, on-demand water heaters warm water almost instantly as it passes through a smaller mixing chamber/heat exchanger.

(There are hydronic water heaters from companies like Alde and Aqua Hot, but that’s a whole different ball game.)

The heating element is much, much more powerful! On-demand water heaters are typically rated between 40,000 and 60,000 BTUs!

Rather than listing a GPH recovery rate, on-demand water heaters are rated by their continuous flow in gallons per minute (GPM). The Furrion tankless water heater, for instance, delivers between 0.38 and 2.4 GPM.*

*However, I must warn you: You won’t get 2.4 GPM across all scenarios! If you’re using chilly 40-degree water from an unheated freshwater tank and heating it up all the way to 120 degrees, you probably won’t get 2.4 GPM. The water temperature will drop; the heating element won’t be able to keep up.

Pros of a Tankless Water Heater

Never Run Out of Water

This is the #1 reason to get an instant water heater! No more rinsing body wash lather only to scream out “Oh COME ON!!” as you get splashed with frigid water.

So long as you have water in your tank or are connected to pressurized city water, you’ll have hot water whenever you want it. Whenever. you. want. It.

Very Lightweight

If you’re driving a big rig, you don’t care about the weight of your water heater. But for pilots of Ford Escapes, Honda CRVs, and Silverado 1500s, a hundred pounds isn’t anything to sneeze at!

Water weighs about 8.3 pounds per gallon. So a regular 6- to 10-gallon tank water heater carries 50-83 pounds of hot water. Plus the weight of the appliance itself, which is usually 20-30 pounds.

Tankless water heaters weigh 5-30 pounds and don’t come with the excess weight of hot water!

No Waiting / No Planning

Using a regular water heater requires either waiting 10-20 minutes for the water to heat up, or planning ahead to turn on the appliance ahead of time.

No such strategy with an instant water heater. Flip a switch; take a shower!

No Temperature Spikes

A good on-demand water heater delivers water at a consistent temperature by monitoring the output temperature. A good appliance can maintain warm water a target temperature plu/minus 2-3 degrees Fahrenheit.

Freeze Protection

Some RV tankless water heaters have a sensor that detects when the line temperature drops to 40 degrees or below. If that occurs, the water heater automatically circulates warm water in the supply lines to prevent pipe freezing.

Easy to Store

Many on-demand RV water heaters can be wall-mounted inside cargo or cubby compartments. That’s a lot easier (especially for renovations) than conventional tank heaters, which require valuable floor space footage.

Cons of a Tankless Water Heater

Minimum/Low Flow Rate

If the water heater can’t sense water moving, it won’t heat anything. So on-demand water heaters have a minimum operating flow rates (usually around 0.4-0.8 gallons per minute). If you’re just trickling water, you won’t get any hot water at all!

On the other hand, you can’t go too fast, either. If Bob’s washing dishes, Susie’s in the shower, and Sasha’s washing her hands in the bathroom, someone is going to get cold!

Limited Electric Power

Unlike conventional water heaters, tankless water heaters really have to run off propane. Most on-demand water heaters, like the Truma AquaGo Comfort and the Furrion 2.4GPM Water Heater, only use 12V electric power to operate the controls. Otherwise, the propane does all the work.

Some point-of-use models, like the Bosch Tronic 3000T, are miniature single-appliance water heaters. You’d install one directly underneath your kitchen sink, for instance. But even the smallest point-of-use instant water heaters use 10-15 amps at 120V. Translation: You better be plugged into a 30A (50A preferable) connection, else you won’t be getting any hot water!

Sensitive to Water Pressure

Cheaper on-demand water heaters may not maintain a set temperature depending on water pressure. With these models, less pressure = less water flow = higher water temperature.

If you calibrate your water heater for 105 degrees Fahrenheit based on a 35 psi pressure from your 12V water pump, and then you switch over to 65 psi city water, you could get far colder water!

Tankless Water Heater FAQs

Can I replace my regular water heater with a tankless RV water heater?

Yes, you can! Many tankless water heaters are designed to fit the same hole opening sizes as industry-standard appliances from Dometic and Atwood/Suburban.

Depending on your RV, you may need to replace your LP hoses and/or power wires to allow large amounts of propane/electric current to pass through.

Be aware that DIY installation may void the manufacturer’s warranty. However, there are many online resources to help you install your own RV water, if you choose.

Here’s a tutorial on how to install the popular aftermarket Girard tankless instant water heater.

Are instant RV water heaters more expensive?

As a rule, yes, they are. Tankless water heaters cost anywhere from $400 to over $1,600! Personally, I would ignore any water heater that costs less than $600. It’s probably junk.

Don’t forget to account for the cost of installation! If you’re considering the award-winning Truma AquaGo instant water heater, for instance, you’ll need to schedule a professional installation from a trained installer. It ain’t cheap!

Do tankless water heaters need to be maintained?

Yes! All RV water heaters need to be winterized.

And no water heater is immune to calcification from hard water (although tankless water heaters tend to last longer). You’ll need decalcification tablets or other products to cleanse your water heater from the inside out.

Can on-demand RV water heaters be operated in the winter?

Yes! Well, kinda. Anytime the weather dips into frosting territory – usually considered 40 degrees or below – an RV water heater is in danger.

Tankless water heaters are particularly susceptible because the small water lines and tiny mechanical passages allow water to freeze much faster than a big, giant, 6-gallon tank.

So tankless water heaters CAN be operated in winter so long as A) they’re located in a warm place and B) they’ve been warm for some time!

RV Water Heaters Data Sheets

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