Jump to content


Photo

On demand water heaters (propane)


  • This topic is locked This topic is locked
16 replies to this topic

#1 TheLandYacht

TheLandYacht

    Full Member

  • Validated Members
  • 12 posts

Posted 30 May 2012 - 07:30 PM

Anyone on here have/use a propane-fired On-demand water heater? I'm trying to get a bead on how much fuel they burn for a given amount of use. Say for one shower a day & a load of hand-washed dishes every couple of days? How long will a 40# bottle last me?

I'm looking at this heater right here.

#2 Rif

Rif

    Major Contributor

  • Validated Members
  • 4627 posts
  • SKP#:84860

Posted 30 May 2012 - 09:28 PM

I'm not familiar with the water heater you linked. Since it requires a 120V connection it would not be common in most RV's.

I have a Precision Temp RV-500. In addition to using propane for heating water we also use it for cooking, and until the middle of last year for our refrigerator. The best guess I can give you about the amount used for heating water is based on our summer purchases of propane. Checking my records it appears that we get from 2 to 4 months from a 40# bottle. What part of that is heating water and what part is cooking and refrigerator is impossible to break out.

Also, keep in mind that there a a lot of variables. For example, we have a washing machine that runs 2-3 loads a week. We also have a dishwasher that runs every day or two. There are two of us so that adds up to quite a few showers. All these things and more, like the temperature of the incoming water, will have an effect on how much propane will be used.
2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter

#3 Kirk

Kirk

    Major Contributor

  • Weekend Moderators
  • 21134 posts
  • SKP#:60541

Posted 31 May 2012 - 06:10 AM

I am no expert in this, but having considered them I would also make sure that the one which you select is rated for RV use, as not all of them are. The problem of needing 120V power is also an issue, but could be supplied by an inverter. I did find several different ones available.

Girard Atwood Precision Temp

Good travelin !...............Kirk
Author & Escapee's Magazine contributor
Full-time 11+ years...... Now seasonal travelers again.
Kirk & Pam's Great RV Adventure
dolphins.jpg
 


#4 Chad Heiser

Chad Heiser

    Senior Member

  • Validated Members
  • 389 posts

Posted 31 May 2012 - 09:44 AM

I have been looking at these on demand propane water heaters for my RV as well. The only question I haven't seen answered about them is how they work with shower head shut offs. When boondocking and trying to conserve water during a shower, we turn the water off at the shower head while lathering, etc. then turn the water back on to rinse and repeat this cycle until done. How does the on demand water heater deal with having the mix of cold and hot water going to the shower head and being stopped there. Does this cause any ill effect. Any one with any experience under these circumstances? I see how they would be great in full hook up sights where water is not a concern. Having unlimited hot water would be great, but I never see any reports on them when water conservation is a concern.

2000 Kenworth T2000 w/ Cummins N14 and autoshift
2010 Montana Big Sky 358RLT

 


#5 Rif

Rif

    Major Contributor

  • Validated Members
  • 4627 posts
  • SKP#:84860

Posted 31 May 2012 - 10:45 AM

They don't work real well if you want to use them that way. They require a certain amount of flow to even fire up, and then they have to regulate the burner to keep the water leaving the unit at the desired temperature. Starts and stops, as well as low flow, are difficult for it to handle correctly.

I addressed the problem with a little plumbing. I installed a line and valve between the hot water line under the sink and the fill line for the fresh water tank. I mounted the valve on the side of the bathroom vanity. Opening the valve causes the pump to run and water to recirculate back into the tank. This serves two purposes. First, it lets us get the water in the lines hot before turning on the sink or shower tap. Therefore we do not waste any water waiting for it to get hot. Second, if I want to take a Navy shower I just leave the recirculation on. The hot water being made while I am soaping up just flows back into the tank and the lines still have hot water in them when I turn the shower back on since the burner is still firing. This has worked very well.

The little plumbing modification I describe could be used by any serious boondocker who wants to conserve water without a lot of hassle, regardless of what kind of water heater you have.
2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter

#6 Neal and Bernice

Neal and Bernice

    Senior Member

  • Validated Members
  • 268 posts
  • SKP#:105972

Posted 31 May 2012 - 11:13 AM

We had some trouble with our Atwood water heater last fall. I ended up talking to the president of the company who was extremely helpful. He went over the top to help us, I couln't have been treated better. At the time I was talking to him he told me they were coming out with a new "on demand" heater. I can't endorse it, because we haven't used it, but he told me they were doing exstensive field testing at the time and would release it about now. This link can tell you more. http://www.atwoodmob...-water-heaters/
2001 FL Columbia (Still Tandem) with Trailer Saver Air Hitch
"Squirt" our 2008 Smart Fortwo
2010 WestPointe
http://neal-berniese...e.blogspot.com/

#7 Lou Schneider

Lou Schneider

    Major Contributor

  • Validated Members
  • 1055 posts
  • SKP#:31721

Posted 31 May 2012 - 11:28 AM

The Eco-Temp heater in the original post is listed as having a 74,000 BTU burner. Propane contains about 91,000 BTUs per gallon. Therefore, the burner will use 74000/91000 = .8 gallons of propane per hour of use.

A 5 minute Navy shower will use about 0.07 gallons of propane. If you take a 15 minute regular shower (or recirculate the hot water back into the freshwater tank during a 15 minute Navy shower) you'll use 0.21 gallons of propane.

Propane weighs about 4.1 lbs. per gallon. A 40 lb. tank contains about 9 gallons, so it can run the burner about 11 hours.

Compare that to a conventional 6 gallon heater that takes about 30 minutes to heat a tankful of cold water. It's 12,000 BTU/hr flame will use 6000/91000 BTUs or 0.06 gallons of propane to heat enough water for a Navy shower.

Tell me again how the instantaneous heater is more efficient than the tank?

Edited by Lou Schneider, 31 May 2012 - 11:32 AM.

Lou Schneider
#31721

#8 Rif

Rif

    Major Contributor

  • Validated Members
  • 4627 posts
  • SKP#:84860

Posted 31 May 2012 - 12:15 PM

Tell me again how the instantaneous heater is more efficient than the tank?

Lou,

Obviously, if you are heating water but recycling it back to the fresh water tank, either with a demand or tank system, you will be using propane that will be wasted, so to speak. If propane usage is your only criteria for purchasing a demand water heater, you will likely be disappointed. But that's not why most people purchase them. The big advantage to a demand system is that you don't run out of hot water. Try taking a 15 minute shower with a standard 6 gallon water heater, or more realistically as happens in our house, try taking a couple showers back to back immediately after running the dishwasher or washer.

We find that the amount of propane used for heating water and cooking is negligible when compared to the amount needed for heating. As I mentioned, a 40# bottle lasts us from 2 to 4 months when not using the furnace, but we can go through one in 2 to 4 days when it gets real cold outside.

One last point, I can't speak to the particular demand heater mentioned, but the Precision Temp (which has a 55,000 btu burner) has valve that regulates the amount of propane being burned so as to maintain the desired output temperature. Therefore, the amount of propane burned would only be what was needed to heat the water to the set point, regardless of the maximum output of the burner. It's like a car. You don't use all 275 horsepower if you only want to drive 35 MPH. It would seem that the amount of propane required to heat a given water would be identical, given equal efficiencies in the heating systems. After all, a btu is defined as the amount of heat required to raise the temperature of one pound of water by one degree. The theoretical advantage of a demand system would be the lack of heat loss during storage as in the tank system.
2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter

#9 Budd

Budd

    Major Contributor

  • Validated Members
  • 3038 posts
  • SKP#:88936

Posted 02 June 2012 - 08:24 AM

I bought a used Precision Temp RV-500 from RV Salvage in 2006. I replaced a working Suburban 10 gallon DSI that had dual heat (propane and 110vac electric). It was never able to deliver a full load of hot water for the washing machine. The RV-500 does not quit. If I want to rinse in Hot (to get the soap scum out), it does.

I am also prone to long hot showers due to fibromyalgia. The RV-500 does this and coupled with a water pik hand held shower, I can get the heat where I need it for as long as I need it to relax the muscles.

Even with all this plus dishes, I use up a 40# tank in about 2 months including a small amount of running dual LP furnaces. This has been measured over the past 6 months and has been pretty consistent.

IMHO, if the difference in the few dollars in the cost of LP from one system to the other is weighed against the inconvenience of not having the hot water one needs when and how it is needed, the bucks lose.

I will say that my RV-500 started having an intermittent problem a few months ago and working with the service guy, the DSI board that fires the burner was determined to be going bad. It still worked but not as dependably as it did, originally.

I got the part, installed it (no brainer) and now it is back to providing perfect hot water.

Folks talk about taking navy showers and we have done that. Depending on how far your shower is from your HWH will make a difference in how long the "cold shot" will be each time you turn it back on. Putting good pipe insulation on the hot water lines will make this a non-issue for brief shutoff periods typical of a navy shower.

Unlike the standard 10 gallon DSI HWH, the RV-500 can let my wife shower in the mornings, then I can immediately follow with my 10 minute+ shower and then she can start a load to wash as soon as I am out. Can't do that with a standard HWH no matter what tricks one tries.

I would not go back. I don't find the gas usage significantly different when one factors out the cooking and heating uses other than for water. Besides, if a couple of dollars makes that much difference to you, most towns with LP gas distributors will sell it by the gallon if you fill 2 or more tanks at one time. They also often have much better pricing/gallon than you will find at campgrounds and other quick mart refilling stations. This can be more of a difference that whatever the slight difference is between an on demand and a standard 10 gallon HWH.

And, as was mentioned, the RV-500 varies the flame so the amount of gas used is up to you. Take a "tiny" shower at .5 gpm and you won't use near the gas you do at 3gpm but it will be the same temps you choose for an unlimited time.

Most of the on demand systems to not have a variable gas supply valve and depend on moderating the output temperature by controlling the flow of water at the faucet. They just run full on or shut off as needed.

RVBuddys Journal Our progress into full-timing.
Budd & Merrily ===-> SKP# 088936 Other Websites:---> Hub of all my blogs
Clifford - 2000 VNL64T770 :: DakotR - 1999 C40KS King of the Road :: $PRITE - 2013 Smart Passion w/cruise


#10 TheLandYacht

TheLandYacht

    Full Member

  • Validated Members
  • 12 posts

Posted 03 June 2012 - 09:17 PM

After doing a bunch of reading,I think I've decided on the EZ Deluxe tankless. It draws the combustion air from outside...then exhausts it back out thru the same flue...by having an oversized flue, with a smaller flue INSIDE it...think a small pipe inside a bigger pipe. Exhaust goes out the center pipe...while intake air comes in thru the bigger part. This also has the advantage that the flue holding the hot exhaust never touches the wall, because the intake insulates it.

Also, since it gets the combustion air from outside, the "unconfined air space" limitations of other tankless units don't come into play, and it can be installed in much smaller space.

#11 Budd

Budd

    Major Contributor

  • Validated Members
  • 3038 posts
  • SKP#:88936

Posted 04 June 2012 - 01:49 AM

Will you have the clearances necessary (12" below, 6" above and in front) and still not be under a window or other opening? That will make the top of the clearance area about 40" above the floor. Also, I was not able to find anything that says how far out from the wall the exhaust vent pipe must protrude on the outside but from the initial drawings, it looks like it is going to have to stick out quite a ways making it unsuitable for mounting on an RV sidewall. There appears to be no flush mounting components.

And please be sure you have a well placed and working CO detector.

RVBuddys Journal Our progress into full-timing.
Budd & Merrily ===-> SKP# 088936 Other Websites:---> Hub of all my blogs
Clifford - 2000 VNL64T770 :: DakotR - 1999 C40KS King of the Road :: $PRITE - 2013 Smart Passion w/cruise


#12 Rif

Rif

    Major Contributor

  • Validated Members
  • 4627 posts
  • SKP#:84860

Posted 04 June 2012 - 08:51 AM

I was going to add another comment until I researched your older posts and discovered you are basically building your own permanent structure using what used to be a rather old RV trailer with most of the RV systems removed. Given that, you can do just about anything you feel comfortable with.
2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter

#13 TheLandYacht

TheLandYacht

    Full Member

  • Validated Members
  • 12 posts

Posted 04 June 2012 - 01:59 PM

Will you have the clearances necessary (12" below, 6" above and in front) and still not be under a window or other opening? That will make the top of the clearance area about 40" above the floor. Also, I was not able to find anything that says how far out from the wall the exhaust vent pipe must protrude on the outside but from the initial drawings, it looks like it is going to have to stick out quite a ways making it unsuitable for mounting on an RV sidewall. There appears to be no flush mounting components.

And please be sure you have a well placed and working CO detector.


Yes. It's going in place of the (already existing) 220v Tankless I already have in the floor-to-ceiling cabinet to the right of the fridge. Unsure what this cabinet was originally for (It's approximately the same width as the fridge was...and a full 6ft tall), because it had already been repurposed as the "piping & tankless water-heater hole" before I bought the trailer.. The whole reason for switching from electric to propane is because that electric heater is a BEAST! a 100amp Service Panel is BARELY enough to run the water-heater (56amps @ 220v all by itself) & all the normal stuff that would run on a 50-amp circuit. I need to ditch the electric WH so I can get below the 50amp threshold in order to be able to plug into a 50amp Park Pedestal (currently direct-wired to the mains at my friend's residence.

I'm sorry if I made this unclear, I wasn't weighing the pros & cons of tankless as a technology...just trying to find out how much it was gonna cost me to switch from electric (tankless) to propane (tankless).

#14 TheLandYacht

TheLandYacht

    Full Member

  • Validated Members
  • 12 posts

Posted 04 June 2012 - 02:01 PM

I was going to add another comment until I researched your older posts and discovered you are basically building your own permanent structure using what used to be a rather old RV trailer with most of the RV systems removed. Given that, you can do just about anything you feel comfortable with.


Reply away! I'm open to suggestions, constructive criticism, even mild flames. I'm brand-friggin-new to this game, so I'll take advice from any corner...whether I follow it depends on whether it fits my particular situation...but I'll certainly listen to it!

#15 GrummanRV

GrummanRV

    New Member

  • All Members
  • 3 posts

Posted 06 June 2012 - 04:43 PM

I have a Bosch propane demand hotwater heater. The thing about demand heaters is they only use propane when you're using hot water so they really end up been very easy on propane. I have a 60lb. tank., cooking uses more propane by far.
I only fill my tank 2-3 times a year.

#16 Doug7155

Doug7155

    Senior Member

  • Validated Members
  • 168 posts

Posted 10 June 2012 - 03:48 AM

We have one in our house and it cut our gas bill significantly. It is about 30" tall, 18" wide and 10" deep and is for the whole house. Great when we have lots of overnight guests as you never run out of hot water.
If you leave a water heater on in the rv it will use more propane than the instant heater. I've forgotten to turn mine off in the RV a few times and it fires up at two or three in the morning keeping that 10 up to temp. Absolute waste of propane.

#17 Desolation Roe

Desolation Roe

    Major Contributor

  • Validated Members
  • 1918 posts
  • SKP#:106407

Posted 10 June 2012 - 06:52 AM

We have a 37,500 BTU in the Suites now. It's too small, particularly for very cold input water.

I consider 50,000 BTU to be a practical minimum, and 70,000 would be better.

Aside from that, love ours. Very easy on propane.

Geo

George, Karen and Bubbles
2008 Volvo 780, 535hp 1850lb/ft D-16 I-Shift, 3.42
2005 Mobile Suites 38RL3

2014 Ford Expedition Limited