All You Need 2 Know About RV Water Heaters & How They Work

For those of you who still juggle the responsibilities of a home and a motorhome, you have a good idea of how your hot water heater back home works. You may wonder how the water heater functions in your RV. Is it more of the same or different?

RV water heaters run on propane, diesel, or electricity and will heat up the water in the tank. Propane or diesel-powered water heaters will have a burning flame that heats the tank, and electric-powered heaters will have a heating element inside the tank that heats it, very similar to a water kettle.

It sounds simple on the surface, I know, but there are a lot of nuances to explain. That’s exactly what I plan to do in this ultimate guide to RV and motorhome water heaters; there are also tankless on-demand water heaters; let’s check them out!

The Types of RV Hot Water Heaters and How Each Works (With Pros and Cons!)

How your motorhome’s water heater works depends very much on the type of heater you’ve selected (or the one that came installed in your vehicle). That’s why I thought I’d get underway by going over the three types of water heaters you can choose from. 

Most RV water heaters that run on propane or diesel can also run on electricity or be upgraded to run on electricity as well; that way you can choose what power source you want to use at any given time!


The first is arguably the most popular and common, and that’s a propane water heater. 

If yours is a propane water heater, then the heater will include a pilot light within. Others utilize a direct spark ignition system. 

Either way, once the fire is lit, the water within the tank will begin warming up so you can enjoy one of life’s greatest creature comforts, hot water!


By far, one of the greatest advantages of propane is that you don’t need electricity. I know that sounds silly when I put it to you like that, but think about it for a moment. 

If you’re boondocking and only can use electricity to warm up your RV water heater, guess who’s going without hot water for a while until you’re done boondocking? That’s right; you are, at least if you want to have power in the battery bank to run all other essentials like your water pump or lights.

A propane-fueled water heater is a lot more boondocking-friendly. You’re now free to unplug and go off the grid for days, if not weeks, as long as you have the requisite amount of propane on you.


As great as propane is as a fuel source for your RVs water heater, I’d be remiss, not to mention the downsides. 

Propane is expensive, and you’ll need a lot of it. You’ll pay more for a jug of propane than you will for natural gas. 

The costs will add up depending on how often you run your water heater and how often you’re topping off the propane levels. 

In the summer, I turn on the water heater about 30 minutes before im going to take a shower, and after im done, I turn it off; that way, even a small propane tank lasts forever!

You’ll have to get good at managing and regulating your propane levels. Once you’re out, you can’t keep the water heater running. Sooner than later, you’ll run out of hot water until you stop and buy more propane.

More annoyingly is how long a propane water heater takes to warm up the tank. It’s going to be at least 20 minutes but can take upward of an hour.

Maybe that’s not such a big deal if you’re out exploring the wilderness while the tank heats up, but if you just came in from a long, sweaty day and you want a shower like now, you’ll find yourself up the creek without a paddle! 


The next RV water heater fuel source is diesel. 

I won’t go into much detail here since diesel works pretty much the same way as propane. Diesel water heaters are a lot more uncommon though. 


The same benefits as above apply, for the most part. If your motorhome’s water heater runs on diesel fuel, you can enjoy all the freedoms of boondocking that electricity will never grant you. That’s an awesome feeling. 

The best part about diesel-powered appliances in an RV is that you have diesel available everywhere, and refilling your diesel tank will never be an issue!

Just remember to keep an extra jerry can with you if your appliances are connected to the main diesel tank that you run the engine from, so you have a backup in case you run out of diesel while camping so you can get going again when it’s time to move.


As I said before, diesel is still quite an uncommon fuel source for water heaters, although it’s on the rise, and more and more models are coming up. that’s going to make it harder to find diesel water heaters and maybe spare parts as well.

Then there are the fuel management issues, as was the case with propane. 

Oh, and cost. I have to talk about the cost. Propane is expensive, as I said, but it costs about 50 percent less compared to diesel’s price tag. Ouch! 


That brings us to the third fuel source for RV water heaters, electricity. 

An electric water heater features a heating element in the tank. When you want hot water, you turn on the heating element, and the water will gradually begin warming, very much like a big water kettle that you might use to boil water for a cup of tea.

Although the important thing is that in most cases, you can only turn on an electric water heater when it is filled with water because otherwise, the heating element will get so warm that it breaks and melts since there is no water around it. Then you will need to replace it!

Learn how to ensure that it is full to avoid breaking it in the video above, or check out this article with diagrams and explanations of how the RV water heater bypass valves work. Before we go into some other pros and cons of electric-powered water heaters.


Expensive fuel sources that are a pain to procure and can run out quickly? Not with an electric water heater for your motorhome!

You won’t have to track down diesel or propane at all hours of the day and night to enjoy some hot water. You’ll always have a reliable source to generate heat if you are connected to a power grid that is up and running properly.

Another advantage is that if you connect your RV to shore power, which sometimes is included in the campsite fees, you don’t have to pay a cent extra for your hot water. That’s an awesome feeling, especially considering how expensive diesel and propane are.

Although sometimes you need to pay for how much electricity you use, then electric water heaters could be more expensive depending on the current prices.


As handy as electricity can be for warming your motorhome’s water heater, there are some downsides to be aware of.

For starters, there’s the boondocking issue. Once you’re off the grid, you’re off the grid, and that means bye-bye electricity. 

There are many things to learn when it comes to an RVs three different electricity systems before you can go boondocking but don’t worry, I have made a beginner’s guide that you need to watch to get ready.

As I mentioned, you could use 12-volt power for your water heater, but that brings me to my next point.

Compared to propane heaters, an electric water heater takes quite a while to warm up. I’ll talk more about how long a little later, but you could deplete your battery waiting for the tank to get hot.

That makes electric water heaters decidedly bad for boondocking. 

How Much Hot Water Do You Get with an RV Hot Water Heater?

RV water heaters are pretty cool, but they’re not comparable to household water heaters in both how they work and their size.

A household water heater can store upwards of 50 gallons (190L) of water. The water heater in your RV, motorhome, or trailer will hold anywhere from 2,5 to 10 gallons (10-40L).

I know what you’re going to ask – how long of a shower can you take with six gallons of water? 

In a standard shower such as those installed in your bathroom at home (again, assuming you’re not a full-time RVer like yours truly), you suck up about 2.5 gallons (10L) of water a minute.

That’s a scary statistic, but you must remember that RV showers don’t use nearly as much water.

I talked about as much in my post about how long you can shower in an average RV. Really, as much as it comes down to the size of your water tank, it’s also a matter of water flow.

If yours is a six-gallon tank (23L), then on a low flow and in water temperatures of up to 100 degrees Fahrenheit (38 degrees Celsius), you can shower for 34 minutes. You’ll have at least 20 minutes of hot water with a medium-flow shower at the same temperature and 13.6 minutes when your shower operates at the max flow. 

What about a bigger 10-gallon water tank?

Assuming the water temperature stays consistent (38 degrees C or 100 degrees F), showering with a low water flow will produce 56.6 minutes of warm water. You’ll enjoy 33.3 minutes of warm water with medium-flow water and 22.6 minutes of heat at the max water flow.

I’m sure you envisioned taking military showers in your motorhome where you have to turn the water off in the middle of bathing to conserve the heat, but no.

If your motorhomes water heater has a 10-gallon tank that gets as warm as mine at 60C or 140F and you shower with a high water flow, you’ll get as much as 22.6 minutes of hot water, so you don’t even need to hurry up! But check out more about how I calculated this and other options in my article.

How Long Does It Take for the Water to Heat Up Again?

Inevitably, you’re going to run out of hot water. Then it’s your RV water heater to the rescue.

How long will you wait for the water heater to warm up so the next person in your vehicle can shower? 

That depends on what type of water heater your RV is equipped with. 

Going back to what I talked about earlier, propane water heaters warm up in 20 to 50 minutes. Diesel water heaters should take about as long to get hot.

That’s not a short amount of time by any means, but it’s not the worst in the grand scheme of things, especially when you look at the warmup times of an electric water heater.

I promised I would talk about this, and now I finally am. 

If yours is a six-gallon water heater, you’ll wait an hour for the water to be hot enough for bathing. A 10-gallon tank requires an hour and a half to heat up. 

Yeah, that’s not so great if you have several annoyed friends or family members in line for a shower. You’ll have to become very strategic about who uses the hot water and when. 

Maybe military showers aren’t so bad! But also, if you have a larger water heater that takes longer than about 30 minutes to get warm, I would consider having it turned on the whole day. Compared to mine, that takes about 20-30 minutes to get warm, so I turn it on before I need it.

What Are On-Demand Water Heaters? What About Combination Furnaces/Heaters? 

Considering the inconveniences of motorhome water heaters, it’s unsurprising that some RVers look for alternatives. One of the most popular options is an on-demand or tankless water heater. Combination furnaces/heaters are also viable.

Let’s take this section to explore both options. 

All About On-Demand Water Heaters

Tankless or on-demand water heaters have many more nicknames still, including instant-on, flash, inline, or continuous-flow water heaters.

As the name implies, an on-demand water heater will provide hot water instantly. All you have to do is turn on your motorhome’s hot water faucet.

How can the hot water be so fast? The pipes in the heater warm up rather than the tank. The water travels through the pipes and heats up in kind.

Even better is that a tankless RV water heater includes a control panel that you can configure to your heart’s content. If you prefer your water warm, but on the lukewarm side, you can reduce the water temperature.

You can raise the temperature for those who can only shower in steaming hot water. 

Tankless water heaters offer so many advantages. You only need a source of water to your motorhome and a source of power, be that electric or propane, and you can enjoy as much hot water as you want.

Seriously, it never runs out, so if you need to or want to take a 40-minute shower, then go for it!

If you normally run your water heater all the time, you’ll reduce how much electricity or propane you’ll use when going tankless compared to a standard RV water heater.

Still, since the tankless heater needs to heat up the water in a very short time, it uses more power to get that done but just for a short amount of time compared to a normal heater that uses a bit less power but all the time. So depending on your habits, this could help cut your utility bills a bit.

That said, an on-demand water heater is costlier, and fitting one into your RV can be challenging since the shape isn’t identical to a standard hot water heater. 

All About Combination Furnaces/Heaters

The next alternative option you might consider for heating your motorhome’s water supply is a combination furnace/heater. 

You get both a furnace and a water heater in one. You can now enjoy hot water and a warmer RV through one device. 

This is the solution that im having in my RV. It’s quite genius actually, and very simple; in the center of the furnace/water heater is the burning chamber where the propane flame burns, and around it is a heating element and then the water tank that gets warm. The excess heat is blown out throughout the RV via air ducts, and viola, you got both hot air throughout the RV and warm water at the same time.

Even if your RV is on the bigger side, you know how much space your furnace and water tanks take up. Imagine condensing them into one. You’ll save so much space and money as well.

After all, you can buy the all-in-one and call it a day rather than replace a water heater or a furnace separately. 

Do keep in mind that if something goes wrong with one part of the combination furnace/heater, both parts might fail, leaving you wishing for a separate furnace and water heater again! 

Can You Leave Your RV Hot Water Heater on All the Time?

You know so much more about motorhome hot water heaters, but you still have another question. Do you have to turn the water heater on only when you want to use it, or is it okay to leave it running all the time?

Technically, you can leave the water heater on all the time if you really want to. This does afford you the advantage of always having hot water at the ready, which is especially crucial if you have an electric water heater.

However, you’re needlessly wasting energy keeping the water inside the tank of the water heater warm when you are not using it. That will depend on your preferences, how often you use warm water, how long it takes to heat it up, and what it costs you to keep it warm all the time.

Like I mentioned before, if you have electricity included in the campsite fees, why not run it all the time, if you like to take a warm shower directly when you wake up in the morning, maybe it’s worth it for you to keep it running. If you want to shower later at night and dont mind doing the dishes with cold water, maybe you should turn it on before shower time.

So yes, you can always leave it on while camping, but what is the best option for you?

Although there are some times when you should turn it off!

Generally, you should not run a water heater, fridge, or any other appliances on gas, propane, or diesel while driving if you do not have a crash sensor connected to your propane system. The consequences could be severe if you crash or rupture a gas hose while driving, and illegal in many cases.

Also, remember that when you power any appliances on propane or diesel in your RV, there is a controlled fire going, an open flame, whether that is behind your fridge or in your water heater; what happens when you stop at a gas station to fuel up your RV is that you are standing next to the fuel pump with an open flame!

But more on that in the video above, or if you want to check out the article I’ve written to learn more about the European laws on the subject.

How to Maintain Your RV Hot Water Heater 

Besides proper usage, maintaining your RVs water heater is another way to keep it in operable condition for a long time. Here’s what I recommend you do at least once per season.

Clean the Flue Tube

Propane water heaters will include a flue tube, also known as a burner tube. If you retire your motorhome for the off-season, It’s recommended to clean this out as debris can gather, which could start a little fire there when you start the heater the next time, which we want to avoid.

You don’t need much to return the flue tube to pristine condition, only a nylon bristle brush and some compressed air. 

Use the bristle brush first, cleaning out the tube as much as possible. When you’ve minimized the debris, only then should you reach for the compressed air. 

Keep the Vents Clean

Across the water heater are a series of vents. Like any vent, these can get blocked up by dust, dirt, and other debris.

You should check and clean the vents more frequently than once or twice a season. Ideally, it would be best to do this at least every month.

Flush Out the Water Heater

Calcium and other minerals can accumulate in your RV’s water heater, especially if you don’t bother flushing it out. 

The more time you spend in your motorhome, the more frequently you should flush. If you’re a part-timer, plan to flush the water heater system at least twice yearly. Full-time RVers should double that.

To flush, first, remove the drain plug to release all the water. I’d recommend letting the water cool down first to avoid potentially burning yourself. 

Then send fresh water through the system. You can also use a water heater rinser to dislodge debris. 

Next, replace the drain plug and refill the tank afresh. 

Change Out the Anode Rod

The RV water heater maintenance process’s last step is replacing the anode rod. This rod collects corrosion and rust, so the tank itself doesn’t rust out.

Anode rods last at least a year but up to three years. More frequent use of the water heater will require you to replace the anode rod about every year. 

This is not something that my fellow Europeans and I need to worry about since most of our RV water heaters don’t use this type of system.


Motorhome and RV water heaters provide warm water for cooking and especially bathing. Most water heaters run on electricity or propane, but some use diesel. 

The type of water heater your RV has influences more than how the heater works but also how long you’ll spend waiting for hot water. 

If you’re unhappy with the current timeframe for your water heater to warm up, you can always look into a tankless water heater instead! 

Rikard Adamsson

Hello! My name is Rikard Adamsson; I am the creator of I live full-time in my motorhome, and right now, I am traveling through Europe the right way, without campsites; yes, wild camping and being off the grid works excellent even in a real beauty from 1996. I have done a lot of rebuilding and upgrades. I am happy to share my experiences with everything regarding motorhomes, RVs, or caravans with you here at

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