Tankless Hotwater Heater

[ddowler]

2003 Montana
Can a tankless hotwater heater be installed?

[Tranquilty1]

My RV dealer is installing one now on my Laredo 266rl. Keystone apparently had some issues and will not install an on-demand hot water system (according to my dealer). I'm also led to believe it fits best on an existing 6 or 8 gal hot water system, but not on a 12.

[hankaye]

Tranquilty1, Howdy;

Have been thinking about one of them for awhile...
Would appericate it if you would follow-up with how it works out for you.

If you wouldn't mind tracking a few things like propane usage ...etc. would be nice :D.

Thanks for thinking it over,

hankaye

[Bob Landry]

I would like to know what Keystones's issue with it is.

[ddowler]

I too would like to know what issues Keystone has. Also if they have a particular Brand and model. Or tankless in general. There are several, both gas and electric models has anyone known of a brand or preference of gas or electric?

[Johnnyfry]

I have had some experience withe such heaters in laboratory vans, which are not unlike trailers. The major problem is the rate of power consumption.

For example: assuming a 2 gallon/minute flow rate and raising 50 degree water to 110 degrees requires 960 BTU/ minute or 57,600 BTU/ hour. At 3,420 BTU/ hour per kilowatt this translates to 16.8 KW which would require 70 amps on a 240 volt circuit. That is a lot of juice!

Even with a unit half the wattage which would give a 1 Gallon/minute flow rate it would require 35 amps at 240V and would put quite a crimp on a 50amp trailer park outlet.

A gas unit to do the same job would have quite a hefty burner and Gas consumption rate. I don't have the BTU per gallon figures for propane at my fingertips.

I would check with the dealer and find out the power consumption, temperature rise and flow rate before you make a decision.

I am pretty sure of my figures, but anyone is welcome to check them.

IMHO,
John

[Johnnyfry]

Following up on my last post. Propane has an energy content of 91,333 BTU/gallon. This translates to 1.59 gallons/hour when the heater is running.

John

[hankaye]

Johnnyfry, Howdy;

Not disputing your information. However, these are set to heat a spiral wraped section of tubing not a bulk tank. The heat is directed to smaller areas over a longer sectionial length. Sort of like a Moonshiner's coil for cooling only for heating. The coil increases the amount of surface area that is either being cooled or heated.

It takes, what 40 minutes to cook up a 6 gal. hot water tank from a cold start? Give or take a few minutes...

If you had an 8' section of stainless tubing with an ID of 3/8ths inch (OD of 5/8ths. inch), that was coiled up into a stainless box that measured 6" X 6" (where the heat is applied), and ran the same 6 gal. of water thru it how long do you figure it would take to heat 6 gal.? After the inital water had run thru it, it may be hot enough for a shower and then continue to maintain that amount of heat.

The difference is that between heating a Large (Bulk) amount of static water to heating a small amount of transiant water in an engineered amount of space.

Think of a water drinking fountain in reverse ... ;)

hankaye

[Johnnyfry]

Hank, I understand that. The flash heater is designed to have low thermal mass so that it reacts quickly when flow begins. The heat is controlled by a flow switch so that connection is made or gas flows only when water is actually flowing. There is no storage.

It is a flow dependent device and the temperature rise of the water is dependent upon flow rate. you can get by with a smaller element if the flow is cut down. A unit allowing 1/2 gallon per minuite could achieve the same temperature rise with 1/4 the power on a 2 gallon per minute rated unit.

It's all about the temperature rise and rate of flow. Given the conditions I stated (2 gal/min, 60 degree rise) would require a heating element the size I stated -- you can't fool physics.

I picked my conditions for a reason: inlet temperature based on average well water temperature in the northern US, flow rate was based on the typical shower head consumption rate, outlet temperature was based on water just a little hotter than most of us would find comfortable so that a little cold water flow mixed in would be needed to reach the optimum temperature.

I know that the power consumption figures seem surprising, that is why I went through the exercise of running the numbers. Check out flash heaters in a catalog like Graingers and you will see what I mean.

My point is that the buyer really needs to be aware of the performance figures on what he is getting so that he will not be disappointed after the job is done. If he gets a unit sized to give a 30 degree temperature rise at 1/2 gallon per minute he had better like cold showers under most conditions.

Personally, I feel that the typical 6 gallon tank heater will probably give much more satisfactory performance overall, but that is me.

Regards,
John

[hankaye]

Johnnyfry, Howdy;

What prompted me to question your numbersis the following link.
I'm NOT connected to these folks in any way/shape/ nor means...

http://www.houseneeds.com/shop/heatingproducts/waterheating/rv/rv500waterheatermainpage.htm

This is the advert that got me interested and asking questions ...... so I ask questions....

hankaye

[Johnnyfry]

Hank,

Thanks for the link. I went there and checked out their specs. I looked at the electric unit first. The model tempra plus36 will heat 4.2 gallons/hour with a 60 degree rise, or roughly twice as much as my stated conditions ---BUT the unit consumes 36 kW or roughly twice as much energy as what I figured. 36kW at 240 volts is a whopping 150 amps, certainly far beyond what any RVer would have available.

Checking out the gas unit, it is rated at 55,000 BTU/hour ( I used 57,600 in my calcs so we are very close) Propane weighs roughly 6 lb/gallon and produces 91,333 BTU/gallon. A 30 pound tank would last about 3 hours of water heater time.

The House Needs web site figures matched up to mine almost exactly, we are all singing from the same book. Physics is physics anywhere.

The primary advantage to flash heaters is the fact they can continuously produce the same flow/temperature--forever, or at least as long as the fuel source lasts. A 55 kBTU/hour flame is as big as a furnace In a small house in the northern part of the country, in other words, a big Flame.

Regards,

John

Going on the road next week! For six months, am I excited!

[Firecapt]

Try looking at this site:

http://www.precisiontemp.com/

:D

[Johnnyfry]

That R-500 unit looks very interesting. While it uses a lot of gas while running, BTUs are BTUs and you have to expend the same number to heat a given amount of water no matter quickly (flash heater), or slowely (tank heater). My major issue was the sie of the burner needed (and 55kBTU/hour is certainly big) they seem to have done a good job of packaging and setting it up foe 12 volt controls.

Of course, an electric unit would be out of the question for the reasons in my previous post but the gas unit could be a winner, certaunly for a family. The big win is certainly the continuous flow.

Thanks for the link.

John

[Tranquilty1]

I've been using my Laredo 266rl with a tankless water heater for almost a year now. I can't speak to specific propane usage. However, the water heats in about 5 seconds and remains as hot as I like for as long as like my showers. I don't seem to need propane fills any more often than fellow campers who cook about the same as me. I'm a full timer who also has a Splendide washer/dryer combo and goes thru between two and three wash loads a week. I'm also convinced that the about 50lb saving of the hot water tank helps fuel consumption at least a little.

[D&L]

I spoke to a person in the Montana factory that I have become friends with and he told me that they looked at a tankless and they use too much propane vs a standard heater.

[Roberson4]

Interesting! Looking at the installation manual for the RV-500.

"Do not install the water heater or any other appliance where it can vent into an area covered by an awning, canopy or any other enclosure."
"Do not install where the vent is closer than one foot from any window or opening into the coach."

Although our water heater is not tankless. It is none the less gas. Seems Keystone did not follow the above recomendations when installing our water heater. It is within a foot of the door and vents into an area covered by an awning.:confused:

http://www.keystoneforums.com/attachments/photobucket/img_37556_0_49b0b03d40f575d29e5a09f138f4dba7.jpg

[Tranquilty1]

I've been using my tankless water heater for about 10 months (I'm a f/t'er). It works great. Only takes about 5 seconds to heat my shower water. The clothes washer has been doing a great job. I'm convinced the loss of the about 50 lbs usually in the hot water tank saves a bit on mpg. I have no idea how to track the propane used only by the hot water as I cook a lot and used the furnace when cold weather camping. Over the past 10 months I've gone thru a total of 210 gals of propane (7 fills of a 30 gal tank) and that includes Virginia in Jan and Pennsylvania/New Jersey in Feb & Mar. I do luv my long, hot showers!

[Johnnyfry]

I am glad to hear your report with the propane unit. It does sound like a reasonable to go.

I made an error in my last posting, I stated that propane weighs 6 lb/gallon. That is incorrect, propane weighs about 4.6 lb/gallon. Big difference because that means that a 30# tank holds a little more than 6 gallons rather than 5 for the figure I used.

Electric is still out due the heavy current requirements.

John

[rhagfo]

Food for thought on tankless heaters, if the flow is real low they don't come on. Sorry 5er at home us Condo camping in Hawaii. The tankless heater doesn't work on a real low flow. If you are without drain and need to conserve they might not be a good choice.

[hankaye]

Johnnyfry, Howdy;

In an earlier post I'd placed a link tho an 'older' type of Tankless H2O heater.
I just got off the phone with the makers of the Girard tankless heaters.
they make 2 versions of the same heater, one is supplemented for winter use.
Has a thermostate that gives it a burst of heat every-so-often to keep water in
the lines from freezing. Girard dosen't sell them direct, however,
Dyers has them on sale now;

http://www.dyersonline.com/girard-tankless-rv-water-heater-with-winter-use.html

DISCLAIMER: I don't work for either Dyers or Girard. In any capacity what-so-ever.

Free shipping and they throw in an oxygenitics showerhead too... (don't work for them either!)

hankaye

[nitro4you75]

Hi all....just following back up on this post......are you still happy with the tankless? im considering one....

[blackty]

Propane weighs 4.2 lbs./gal.
30# tank holds a little over 7 gal.
30 gal. tank, also called a 100# tank, filled to 80%(industry standard) holds 24 gal. Those are the tall skinny ones at homes for cooking or at seasonal sites for whole trailer.
Just to clarify for those comparing usage.
Also the gas line feeding the water heater needs to be larger to allow enough volume of gas to flow at the specified pressure.
Hope that helps...Jim