I'm planning to use two on-demand water heaters on my RTS to save energy

[Kevin Warnock]

Hello,

Today I wrote up on a my blog a long article about my plan to use two on-demand propane water heaters on my RTS bus conversion:

http://kevinwarnock.com/2012/02/15/dual-on-demand-water-heaters-for-redundancy-and-extreme-efficiency/

The concept is as follows. Install two 1.6 gallon per minute propane on-demand water heaters. One should be vented with a chimney and  one should be a vent free model with a low oxygen sensor. The vented model costs about USD $175 and the vent free model costs about USD $210. Place a 3-way valve near each faucet.

When it's cold outside, turn the 3-way valve so that the vent free water heater will be used. The water will be warmed, and the substantial amount of heat that isn't transferred to the water will be exhausted right into your living quarters to warm the air.

When it's hot outside, turn the 3-way valve so that the vented water heater will be used. The water will be warmed, and the substantial amound of heat that isn't transferred to the water will be mostly sent up the chimney, thus lowering the burden on your air conditioner.

If you need lots of hot water, you could set the 3-way valve in in the middle, and run both water heaters together.

My plan gives you a backup water heater as an added bonus.

I go into more detail on my blog, so I invite you to read the full description there.

I would love to read your comments about my plan.

Finally, please friend me on Facebook at http://facebook.com/kevinlwarnock. I am friends with some of you, and I love reading your status updates and getting to know about your lives away from buses.

Thanks,

Kevin Warnock
http://KevinWarnock.com - my blog

[TomC]

Sounds like a good plan.  I like simplicity-so I have 2-10gal electric water heaters-one plumbed into the next with the last one wired through the inverter.  No propane, no chimney, and except for draining once a year, no maintenance since I installed them in 1994.  Granted they do take more space then the instant, but I like the redundancy, simplicity, and ability to get a new heating coil at any big box store (of which I haven't had to yet).  Then have a simple 40,000btu propane furnace. Good Luck, TomC

[Kevin Warnock]

Tom,

I had an electric water heater in my MCI. What I didn't care for was needing to start the generator first thing in the morning to take a shower. But I loved the reliability. I didn't have to do anything to it for the 10 years or so that I had it, and it was on the bus when I bought it converted, so the heater itself was perhaps 20 years old when I sold the bus last year. I would be shocked if these inexpensive propane on-demand units last for 20 years with no service. However, they are so inexpensive they can be thought of as replaceable if something goes wrong. I don't like thinking like that, but, to my knowledge, there are no premium vent free propane low capacity on demand water heaters -- just the low cost $210 model I linked to from my blog.

How's your truck conversion coming along?

Kevin
http://KevinWarnock.com - my blog

[Oonrahnjay]

Kevin - Don't have any experience with on-demand in a bus but I put one in my house (had a major failure in conventional electric heater) and it's been very good.  Low cost to run and works perfect. 

[Seangie]

Kevin,

I am looking at tankless water heaters as well.  Biggest reason is that there will be 6 of us taking showers and I don't think the 10 gallon tank we have now is gonna cut it.  I like your idea about the 2 heaters.  We have a webasto heater on board and I was going to look into using that as the backup water heater.

Let me know how the tankless heaters workout once you get everything setup.  I'd like to see how you install and vent the one heater.

-Sean

[Lin]

I had a tankless Paloma in my last bus.  It worked out okay.  Unless you get a really large one, they keep the GPM down, which is not bad for busing anyway.

[JimG]

Keep in mind on the vent free, besides the exhaust you are subjecting the interior of your coach to the moisture, etc. from the propane. This is a caution that you need to take into consideration. Jim G. - RTS-II

[Sean]

Kevin,

I am not a fan of tankless, aka "on-demand" water heaters in bus conversions.  Whether or not they can "save energy" is debatable, and highly dependent on how you use your bus.

We have a 12-gallon marine-type water heater and we use virtually no energy at all to get hot water.  That's because we get all the hot water we need for free when we drive from waste engine heat, and when we are parked without hookups, we get hot water from excess generator capacity when we run the genny daily to charge batteries.  And, of course, if we have a shore power connection, even as small as 10-12 amps, we get all the hot water we need from that as well.

By contrast, on-demand water heaters use fuel every time you need hot water.

To put this a different way, a tank-based water heater allows you to make the hot water when the cost of heating it is low (or zero), and use it later, whereas on-demand heating means you need to expend the energy to heat the water at time of use no matter what.

Unless you are in the habit of leaving your tank-based water heater energized 24/7 regardless of need, I am hard-pressed to see how an on-demand heater can ever be more energy-efficient than a marine-type tank-based heater.

For larger families, such as Sean's, I would suggest even larger or possibly multiple marine-type water heaters.  Again, when driving, large quantities of domestic hot water can be generated for free with this system, and on limited shore power, large quantities of water can be heated over longer periods of time with minimal electric load.  Here again, daily generator run time can be used to advantage by scheduling it around hot water demand.

FWIW, YMMV, etc.

-Sean
http://OurOdyssey.BlogSpot.com

[Oonrahnjay]

  (snip) For larger families, such as Sean's, I would suggest even larger or possibly multiple marine-type water heaters.  Again, when driving, large quantities of domestic hot water can be generated for free with this system, and on limited shore power, large quantities of water can be heated over longer periods of time with minimal electric load.  Here again, daily generator run time can be used to advantage by scheduling it around hot water demand.

       I am just experimenting with my generator (and Outback inverter setup), but I'm finding that if I run my generator for a short while to charge the batteries in the morning, my hot water (I have a 10 gallon Atwood heater with the coolant -- or as I like to call it in this situation, the "heatant" -- loop) is "free"; conversely, if I run the generator to heat water with the electric element, then the loop heating and battery charging is "free".

       (Of course, no energy is "free"; you pretty much pay for it one way or the other, but (Odyssey) Sean's point is well taken that if you're plugged into a "limited shore power" point on your own property or you're already paying for a campsite, that power is without direct cost to you.  Also, if you have to make energy for a specific purpose and you're pulling either a minimal additional load to heat water or you're capturing otherwise waste heat, that is either very low cost or "free" energy.
       And my Atwood also has capability to heat water with propane as a backup.  I don't anticipate using it much (I haven't even experimented with it so far) but at least it's available and once I'd selected the heater model with the coolant loop and 120V coil, the additional cost to add the propane feature was minimal.
       So, with my limited experience, I can say that it looks as if Sean's experience of "mostly 'free' waste energy to heat water" works for him and it's going to work for me, too.   Thanks to Gary Throneberry ("Garhawk") for describing his experience with using loop-type water heaters in his past RV's and encouraging me to buy a heater with this feature; it appears that this was good advice.

       As I mentioned in an earlier post, my experience of using an on-demand water heater in my home has been excellent, but spending a similar amount of $$ to install a marine-type water heater instead looks better for my bus conversion.  And what (NC) Sean would pay for two on-demand heaters would cover the cost of a multi-purpose marine heater; even if his family's size means that he would also need two marine heaters to cover their needs, the marine heaters would be an investment that will provide "pay back" versus an extended energy cost in use in the future.)

[belfert]

Personally, I would never use anything ventless in a bus.  Ventless heaters almost always inject a lot of moisture into the air and then you lose heat venting the moisture.  Ventless heaters may not produce dangerous amounts of CO, but they still are putting pollutants into the air.  I've been in buildings heated by ventless heaters and often you can smell the heater running.

I have a vented natural gas fireplace at home.  Even though it is vented it still smells inside when I run it so I almost never use it.  It isn't producing CO since I have several CO detectors on that floor that don't go off.  (The detectors get replaced every seven years.)

I can't imagine you would ever save enough on heating costs to justify carrying around two water heaters and all the required plumbing to switch between the two.

[bevans6]

There are just so many ways to skin this cat.  I can't make the business case work for most of them - I am far less concerned with saving energy than I am with saving money, and I can't make any upgrade to my hot water system pay for itself.  I have the old fashioned suburban RV hot water heater, propane and 120VAC electric.  When I get to where I am going I fire it up, electric if on a pole, gas if parked somewhere.  By the time dinner is done the water is hot to do the dishes, and it's still hot in the morning for my shower even if I turn it off when I go to bed.  That things was setting on the floor of the luggage bay when I got the bus, so it was either free or I paid a ton for it depending on how you look at it, in any case I had it so I installed it.

That's my story.  I am still looking at instant-on propane for my house, but even there it's hard to make a new install pay off in less than around 10 years.  The problem is when you already own a perfectly good all-ways on old fashioned water heater...  the upfront costs kill you.

Brian

[belfert]

I think you have to be on the road for much of the year for the cost of heating water to really be significant.  If you're going from pole to pole at campgrounds electric water heating makes the most sense as electricity is generally included unless you are staying long term.

My parents had to replace their home water heater last year.  They couldn't justify paying twice as much for a tankless water heater just for the two of them.  Tank type water heaters have gotten better over the years.  They no longer have pilots for the most part.

[Seangie]

The number one reason for going with a tankless hot water heater that is not mentioned is the unlimited supply of hot water.  At least until you run out of propane

With 4 kids (3 of them girls) and staying in campgrounds, that would be my main reason for using it.  Again - Using a 2nd (redundant) system that would serve as a main or back up such as Sean mentions with the marine type system that can be heated via the engine or Webasto or generator. 

The creative part would be in how you would setup such a system.  Tankless inline with the tank heater?

Kevin - Not to take away from your original post - I'd still like to see how you set it up and how it all works out for you.  I'm not sure you'd get enough heat from the ventless system to make a big difference but I am still intrigued.

-Sean (NC)

[Sean]

The ... reason for going with a tankless hot water heater ... is the unlimited supply of hot water. ...
With 4 kids (3 of them girls) and staying in campgrounds, that would be my main reason for using it. 

Sean,

I think I understand your situation fairly well, given our extensive discussions a couple months ago, and I firmly believe you need to re-think this.

"Unlimited hot water" implies unlimited sewer, which implies "full hookup site" (I will show the math for this in a moment).

A full hookup site will have essentially unlimited electricity.  If you pay for the site on a daily basis, the electricity will be included, so it is "free."  Even if you pay on a monthly or perhaps weekly basis, where the electricity is metered separately, in most of the country, perhaps 95% or more, the cost of heating water with this electricity will be far, far less than the cost of heating water with LPG or diesel.  So if you really want "nearly unlimited" hot water, given a full-time sewer connection, then you are better off buying a much larger electric tank-style water heater, even if it is as large as 30-50 gallons.  Get one with a good recovery rate, and you might as well go 240, because full-hookup sites will generally have 240 available

If, OTOH, you are thinking that you don't want to use an electric water heater because you will not have shore power available full-time, then that would imply that neither do you have a full-time sewer connection, and now "unlimited hot water" becomes a delusion, as I wrote on the other board.  Hard as it may be to accept, if your girls can't learn to shower with 3-4 gallons of water (only about half of which, or 1.5-2 gallons, will end up coming from the water heater), then you are going to be in big trouble.  Water, and even electricity, is easy to find on the road, but sewer connections are like gold.  Even at campgrounds, a sewer connection, if it is even available, can add $8-$12 per night to the rate.

About that math:  We use about ten gallons of water here on Odyssey per day.  That includes everything; our 135-gallon gray tank will take us at least two weeks and in a pinch we have gone 18 days.  Since there are two of us, that works out to 5 gallons a person.  We don't consider ourselves particularly conservative when it comes to water; we do all the normal things anyone who lives in a house does, except we take "navy" showers.  Still, many would say that our usage is rather spartan.

If your family could manage the same rate, then you'd need to store 30 gallons of gray water per day whenever you are away from a sewer connection.  That adds up fast; with our tank, you'd be able to go four days but not five.  You'd need a 210 gallon tank to stretch to a weekly dump schedule if you were parked someplace where you'd need to move the bus to dump.

I've never measured how much water we use for a shower, but I can guess that we use less than two gallons each.  At that rate, even our 12-gallon water heater could shower your entire family with plenty of hot water left over for dishes.  Even at double that rate, a 20-gallon unit would easily meet your needs, and at that point you'd be storing over 42 gallons of gray water per day.

So the bottom line is that either you are paying for a sewer connection, which means you'll have unlimited free or cheap electricity and therefore a tank-style electric hot water heater will be the most cost-efficient solution, or you need to store your waste water, which would mean having an "unlimited" hot water supply is irrelevant.  In either case, a gas- or oil-fired on-demand water heater (which, BTW, will run you north of $1,000, installed, in the sizes you are thinking) is not the most cost-effective solution.

And before anyone jumps in here to point out that a tankless water heater will take up less space and weight in the coach than, say, a 30-gallon electric water heater, that space "savings" will be immediately negated by the extra tankage you will need for either the LPG or diesel to run it.

JMO, FWIW, YMMV, and HTH.

-Sean
http://OurOdyssey.BlogSpot.com

[Mex-Busnut]

(By the way: Excellent information, Sean!)

Here in Mexico, all of the hardware places sell electrically heated shower heads, which heat the water as it goes through. No separate water heater needed. They are really inexpensive. A guy could have the tankless propane unit for when he has no AC voltage available, and switch this on when you are at an RV pedestal.

Here are some examples from the Mexican version of Ebay:

http://listado.mercadolibre.com.mx/regadera-electrica

Our exchange rate is about 13.50 pesos per U. S. dollar.

And an example on Ebay:

http://www.ebay.com/itm/Coral-Max-Tankless-Water-Heater-Electric-Shower-Head-110V-FREE-Arm-Tube-Support-/260936401581?pt=LH_DefaultDomain_0&hash=item3cc10582ad