Mod #74: Tankless Water Heater

Mod #74: Tankless Water Heater

Submitted on: 03/03/09

     Category: featured, plumbing
Mod Rating: 12345

(89 ratings)

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Mod Description:

So how long can you shower in your RV? I’ll bet for most of you it’s not more than a few minutes before you start to run out of hot water. Of course, you can use the “navy shower” technique and that’s works for most. But for some of you, taking a long hot shower in your RV is something you can only imagine. Your water heater just can’t recover fast enough to heat the cold water coming in to the water tank as it flows out of the tank to your shower head. Oh what to do? The tankless water heater mod of course!

Mod Difficulty:

There are some options to help your factory water heater improve heating recovery time. You can install what’s called a hot rod, which is a electric heating element that replaces the anode rod in your water heater. This rod uses 400 watts of AC power to heat the element and assists the gas portion of the heater with recovery. This is a somewhat viable option for extending your hot water supply time but some water heater manufacturers frown on their usage, stating that it may void the warranty because the lightning rod no longer provides the corrosion protection the standard anode rod does. You still won’t get the hot shower of your dreams with this option though.

Here is where the tankless water heater comes in to play. There are two types of tankless water heaters: electric and gas-fired. The first kind works similarly to the hot rod in that an electric heating element heats the water. But that is where their similarities end. Rather than fill up a tank full of water and then heat it, the the electric tankless heater senses water flowing through it, activates the electric heating circuit, and the water is heated instantly. It is 100% automated. As soon you turn off the water flow, the heater turns off. Water temperature is regulated with water pressure. Less water pressure means more heat, and more water pressure equals less heat.

The gas-fired type works very much the same as the electric heater in terms of sensing water flow and instantly heating it. But in this case, a propane burner heats the water. And there are no large electrical power demands needed as with the electric heater. Both can deliver a steady flow of hot water nearly indefinitely, but the gas-fired type will be able to keep up with demand better, and is more easily adapted within a typical RV environment.

The easiest way to mod your RV with a tankless water heater and get that sensational endless shower is to use an inline device that replaces the shower head. This type of heater uses a powerful electric heating element to instantly heat the incoming water just before it exits the shower head. It can increase water temperature by as much as 50F at a one gallon per minute flow rate. This should be enough to supplement the factory water heater so while it’s recovering, you are still getting reasonably hot water. The only con is that the unit consumes a lot of current, upwards of 20+ amps. You will need to dedicate a circuit breaker and receptacle for this unit should you decide to go this route.

If you’re boondocking, or otherwise camping without hookups, then consider doing this mod with a custom installed gas-fired tankless water heater. These units do an excellent job at providing instant and sustained hot water, and can be used to supplement or completely replace the standard RV water heater. There are a couple of very important things to consider before doing the mod though. The first is the venting requirements. Like your RVs heater, the tankless heater emits CO2 when the burner is on, and the CO2 needs to be vented outside the RV. Three inch tubing is a minimum and should be exhausted through the roof or side wall with the appropriate tubing and vent cap.

You need to also consider where the unit is mounted. The area should be free from anything that could come in to contact with the unit. Also, the unit should have some ventilation or fresh air supply. This isn’t critical but the burner does need oxygen to work. Most standard RV cabinet doors don’t seal very well to begin with so there should be enough air supply to provide proper performance when the unit is mounted in areas like this. In any case, follow the manufacturer’s recommended installation procedures if you are at all unsure. This includes connecting the gas and water supply, and any electrical requirements necessary to power the unit’s circuit board.

Finally, and of course the most expensive of all the options, is to completely replace the factory water heater with a drop in replacement tankless heater made specifically for RVs, the RV500. This is by far the easiest way to have endless hot water. Replacing the standard water heater with the RV500 is surprisingly simple. Start by turning off the propane and draining your water heater. Remove the gas supply line and water lines. And disconnect any electrical wiring. Unscrew the fastening screws on the outside frame of the heater and the unit should slide right out.

To install the RV500, reverse the steps used to remove the factory water heater. Chances are the gas supply pipe and the water inlet and outlet tubing won’t require any modifications and will attach directly. The heater does require a 12-volt power supply in order for the circuit board to function and otherwise control the unit. It’s very low current so you should be able to tap in to most any 12-volt source nearby. Once installed, you just have to turn on any hot water faucet and the unit will automatically turn on. Turning off the hot water faucet in turn shuts off the heater. It’s quiet and will keep up with any demand. Now you can take your time showering but you might have to mod your RV with larger holding tanks!

ModMyRV recommends these parts for this mod:
Bosch 1000P LP AquaStar 2-3/5 GPM Indoor Tankless Gas Water Heater
Portable Tankless Water Heater with Shower Head

General Reference

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21 Comments For This Mod

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  1. jmt

    That’s so cool. I would love to take a 10 minute shower…longer if my DW leaves me in there.

  2. Bob Vaughn

    Ouch…..I checked out the price of the RV500……Little too much for my budget…..

  3. ModMyRV

    Yeah, it is a bit pricey. I guess it would take saving a few quarters you would normally use for campground showers. ;)

  4. jmt

    I just boil extra water if I really need it. :)

  5. Bob Vaughn

    I stayed in a campground that required quarters to keep the water running…..I was in the Navy so I know how to take a quick shower….I got wet, soaped up and the water went off…I know I have a lot of skin to soap up but not that much….I was fit to be tied….I had to get out of the shower to get more quarters out of my pants…..Never again….

  6. jmt

    I lived on a farm when I was young and had to fight for warm water. I know the turn water off thing also. Don’t miss those days.

  7. CoolSitez

    Great article. At the risk shameless self-promotion, you can find the best price on the Internet for the RV-500 at our website. Go to

    Hopefully, nobody will be too mad at me for throwing this in here … just trying to save you a few bucks if you’re interested :-).

    Phil King

  8. ModMyRV

    No worries CoolSitez. Hopefully those that are interested will visit your site. Do you have any pictures of installations you would like to share? Not too many have done this mod…

  9. Bluebird Bob

    We put in the RV500 6 years ago in our older Bluebird.
    It has worked flawlessly for that entire time and recommed it highly!

  10. Captain Slappy

    Now, this is a problem in my ‘78 Starcraft Travel Star that I fought with for over a year (I am a permanent resident in it). How to get a large amount of hot water when I WANT it, which is now.

    I side stepped that issue after yanking out my old original (and severely damaged by previous owner) gas water heater (6- Gallon), by going to Lowes, and grabbing a 20 Gallon straight electric. After a replumb job (the whole trailer was using polybutelene, which was replaced with my friend the Schedule 40 PVC) which also consisted of MANY ball valves, etc. in went the 20 Gallon Electric.

    Suffice it to say, it is most awesome. At a little over 2′, I was able to put it into a badly designed (originally) closet, whose floor was a foot above the cold/hot water supply lines, and life is MUCH better/easier this way.

    As a secondary modification, I also added in a standard, household light switch wired up so I can turn the water heater On/Off on demand, and found that during this summer, the heater could be turned on for 3 hours to heat the 20 gallons of water (per specs), and then turned off for 24 hours, and still be around 80 degrees.

    At the moment, temperatures are around 20 at night, and 50 during the day, so obviously, that time between “turn-ons” is shorter.
    The unit is: Item #: 140403 Model: E1F20US015V 120V
    At a princely price of (12/2009) of $288, it beats any other “mod” quite easily. 1500 watts, the same as a coffee pot!

    Remember, these were originally designed for “small household” use, but they REALLY do the job. Lowes also carries 6 and 12 gallon models, but I couldn’t handle it, and splurged!

  11. Gary

    I have the six gallon conversion that does not work and I did contact someone about it and they said I could mail it to them and they will test the parts. Unfortunately the email is on my computer at home and I cannot get it at this time. If the person reads this please answer.

    Thank you.

  12. Russ

    I installed the RV500 2 years ago. With kids, when you need hot water, you really need it! This thing was expensive, but worth every penny. I wouldn’t have another trailer without it.

  13. Dave

    Anyone put one of these in a park model RV??

  14. John

    I have a RV500. Love it.

  15. Rick

    I have one in my 5th wheel. It is a 12L propane fired, battery ignited model. Works great and easy to convert from the standard water heaters that are in RV’s. I don’t know why RV companies do not use them in new production models. They are on demand, so you only use propane when you need hot water. And now we have endless hot water for showers and doing the dishes, at the same time, if needed. Forget about the electric ones. Go with the propane. You will have Hot water even while on the road, with no electricity!

  16. Tim Donahue

    My propane water heater went out,found a electric on demand heater at Home depot 6gal 12.5 amp draw fits under sink.I camp at sights with 30 amp hookup and no problems,cost 200.00 I run the a/c,tv and some light,pluged in a 1500 watt heater and finaly breaker kicked out.If you like long showers and instant hot water its great,three people take a shower in a row and and still water was at 130 Has a 6 year warrenty on tank!!!

  17. DonW

    Hi there. has anyone looked at using a camp chef or similar external to the camper and just plumb it in parallel to the RV factory tank? is there any reason you couldn’t just plumb into the RV water heater drain tank and supply the external tankless pressure there?



  18. Jim

    I installed an ExcelAmericaa tankless for about $300. Works fine.

  19. Russell

    There are many units FAR less expensive than the ecotemp 500. There’s a company called Marey that has Bern making tankless heaters since the 50s. European RV companies have been using this Tech for decades. So I won’t even bother with “why have’we’easier so long. My question is, has anyone installed a unit OTHER than the ones described here? The Marey units are smaller, lighter and appear to be much more efficient. The trick is that they are not the same shape as the hole in the wall that would be let after removing the old heater and tank. I feel it should be fairly easy to adapt the hole and as described here and the underside of the cabinets will get enough air flow. Or you could simply install louvered ventilate doors and the cabinet doors near the heater, also not tough. But what to do with the flue is my concern. Can you put a 4.5 inch exhaust pipe emerging through the space where the previous heater was? Should be rest enough to make a board to give the hole then insulate. Anyone have any thoughts?

    They cut a hole in the wall in a house when they install these things and the heat transfer doesn’t seem to be an issue but an RV wall is not the same as a stick built house.

    I cannot be the first person to speculate on this. I’m sure someone has installed these in their RV.

    Tampa, FL

  20. Robtetee

    I had one in an old motorhome and it’s just as easy as you think it is; cut a ?” hole in the roof or wall, install some type of heat shield (foil, silicone, ceramic,etc.), and install the flue; some expanding foam or some other “hole filler caulk?”perhaps for the small holes and cracks , If yours is electric, put it anywhere you want, I guess! Good luck & Bon Voyage! (o:)

  21. nicholas

    Can I use a tank less water heater from lowes in my travel trailer

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