Anyone using a tankless water heater?

[BIGRICH805]

Originally Posted by louie

I want to piggy back onto the 33 degree question. The way this heater works is it raises the temperature if the water a max of 33 degrees? So if it's 50 degrees in my van I am looking at an 83 degree shower? This is doable, but those tankless propane heaters look pretty sweet. Is the tank inside the unit with the propane tankless heaters or do you have to somehow run an external propane tank to it?
Thanks, L

The eemax unit IMHO is not suitable for dry camping unless you are going to use a generator. It simply draws way too much juice. 20 amps. The propane tankless on-demand unit mounts inside like the traditional tank water heater SMB puts in at the factory. The propane tank itself is hard plumbed in and resides under the van. The real beauty of this unit is that if you want unlimited time in the shower, all you need is a water hookup at a campsite. Use bio-degradable soap and shampoo and let the grey water just run out on to the ground.

[louie]

What size generator do you think I would need to run the tankless electric. The 33degree version vs. the 48degree? Paul from the Austin shop was doing my best to talk me out of the electric tankless heaters. He claimed they can only raise the temperature of the water by ten degrees? Propane seems like the way to go, but seems like a much more expensive option vs. running my generator with the tankless electric when boondocked.
L

[BIGRICH805]

It will depend on what other electrical draws you will have going at the same time. I would think you will need at least (and this very well could be insufficient) a 2,000 watt genny to run that on demand heater.

Below are some pics of the propane on demand heater in my van.

[Roonie]

Originally Posted by BIGRICH805

It will depend on what other electrical draws you will have going at the same time. I would think you will need at least (and this very well could be insufficient) a 2,000 watt genny to run that on demand heater.

Below are some pics of the propane on demand heater in my van.

Wow that eats up a lot of space.... what I liked about the eemax unit was the size like a small hardcover book. But it does have disadvantages which have been pointed out. I was planning on running engine for 20 minutes if I installed it like our microwave.

May have to forget it all together and use solar showers. Save the rear SMB shower for washing off the dog or feet

[jage]

Originally Posted by Roonie

Wow that eats up a lot of space....

I'd say that's nearly the same size as the Suburban water heater.

[Kzinti2]

Originally Posted by louie

What size generator do you think I would need to run the tankless electric. The 33degree version vs. the 48degree? Paul from the Austin shop was doing my best to talk me out of the electric tankless heaters. He claimed they can only raise the temperature of the water by ten degrees? Propane seems like the way to go, but seems like a much more expensive option vs. running my generator with the tankless electric when boondocked.
L

Water heating is a huge energy hog. Therefore, any electric solution to water heating that does not rely on shore power is problematic. Also, showers can easily be a huge water hog and can quickly exhaust an on-board water supply (such as my 10-gallon system) if another source is not available. Demand (tankless) water heaters that I am familiar with work by supplying a constant amount of heat and varying the water flow rate to adjust the temperature rise from the water supply temperature. Slower flow equals a smaller quantity of hotter water for the same amount of heat input per minute.

Some definitions:
1 BTU = heat required to raise 1 pound of water 1 degree farenheit
1 Watt (W) = 3.412 BTU
1 KW = 1000 watts
1 Gallon (liquid) = 8.333 pounds (# = pounds)
1 cubic foot = 7.48 gallons
Volts x Amps = Watts (V x A = W)

A home-based example:
A somewhat miserly home shower might be delivering 2 gallons a minute of 105 degree water heated from the 55 degree water main temperature (50 degree temp rise).

2 gal./min. = 16.33 #/min

16.33 #/min. x 50 degrees rise x 1 BTU/degree/# = 833 BTU/min.

833 BTU/min / 3.412 W/BTU = 244 W/min.

244 W/min. x 60 min./hour = 14,640 W/hour = 14.6 KW/hour.

14,640 W/hour / 120 V = 122 Amps supply required for a shower with a demand heater
14,640 W/hour / 240 V = 61 Amps supply required for a shower with a demand heater
14,640 W/hour / 480 V = 30.5 Amps supply required for a shower with a demand heater

Yikes! This is twice what an electric stove and oven would consume with the oven heating and all four burners on high. Obviously this is not considered practicable in a typical home due to the large power feed needed to do this electrically. Typically, an all-electric home would have a tank-style water heater and raise the water temp in the tank over time with a much lower power feed. When the hot water runs out, the shower ends rather quickly!

The above example provides some useful context for evaluating the small Eemax electric tankless water heaters that run on 120V (data from http://www.eemaxinc.com/assets/files/sp.pdf ):

SP2412 2400W 120V-20A 33 degree temp rise at 0.5 gal./min. (11 deg. rise at 1.5 gal/min)
SP3012 3000W 120V-25A 41 degree temp rise at 0.5 gal./min. (13.5 deg. rise at 1.5 gal/min)
SP3512 3500W 120V-30A 48 degree temp rise at 0.5 gal./min. (16 deg. rise at 1.5 gal/min)

To be supplied by a generator, the constant generator output rating (not peak or surge rating) needs to be equal or greater than the Eemax water heater demand or you will quickly cook the generator. And this is for a 1/2 gallon/minute shower rate with a lower temp rise than typical at home. If you have the ability to preheat the shower water a bit (solar, engine heat?), than the shower can be hot (72 degrees + 33 degrees = 105 degree shower for SP2412 at 1/2 gal/min.), but otherwise your shower will be not so hot. In warm sunny weather a solar shower may do as well for far less investment.

If you already have a generator of suitable size and have the water availability, the Eemax may be useful. Without a generator, the Eemax probably is not useful since the battery demands are prohibitive. Assuming an optimistic 90% inverter efficiency:

SP2412 2400W 12V-222A/hour or 3.7 amps/minute from your battery (18.5 amps for 5 min. shower)
SP3012 3000W 12V-278A/hour or 4.6 amps/minute from your battery (23 amps for 5 min. shower)
SP3512 3500W 12V-333A/hour or 5.6 amps/minute from your battery (28 amps for 5 min. shower)

A 5-minute shower-run-time will take a big bite out of your battery.

My experience is anyplace that I could hook up already has a shower house and I will use it instead. If I am camped remote but can afford the water (or dip it from a lake, etc.), I will use my solar shower; I heat water on the stove if the sun doesn't cooperate. No, this is not as convenient as at home but I am not willing to pay for and travel in a rig that provides that level of service and luxury, especially without supplemental hookups. If I full-timed in cold weather or populated areas without traveller services, my approach would likely be different.

[cygvan]

I have an EEMAX installed at home. It takes alot of power. It will pull over 200A from your batteries (through your 3000W inverter) while running, unless you are plugged into shore power.

Mike

i read that the eemax draws 20a. how does this translate to drawing 200a from batteries? i thought that means it draws 20 amps per hour. if not, how the heck does one figure how much their battery banks are being depleted by ANY device?

still trying to wrap my head around electrical theory and this confused me. im mostly self taught and clearly there are gaps in my knowledge that need filling but i thought i had the amp rating on devices figured out till now. what am i missing? lol

[cygvan]

If you already have a generator of suitable size and have the water availability, the Eemax may be useful. Without a generator, the Eemax probably is not useful since the battery demands are prohibitive. Assuming an optimistic 90% inverter efficiency:

SP2412 2400W 12V-222A/hour or 3.7 amps/minute from your battery (18.5 amps for 5 min. shower)
SP3012 3000W 12V-278A/hour or 4.6 amps/minute from your battery (23 amps for 5 min. shower)
SP3512 3500W 12V-333A/hour or 5.6 amps/minute from your battery (28 amps for 5 min. shower)

A 5-minute shower-run-time will take a big bite out of your battery.

same question as above

[daveb]

Go to the FAQ section at the top of this section and there is a link to a usuage calculator that might help you out.

[cygvan]

Originally Posted by daveb

Go to the FAQ section at the top of this section and there is a link to a usuage calculator that might help you out.

many of them i came across in the past...the calculators give the answer but im trying to understand why...

so i input 12v 600ah battery bank using a 100 watt appliance and the calculator returns an answer of 30 hours..how does it arrive at that i guess is what im asking...

ive been focusing on the amperage of devices themselves...since the amp hours of the bank is what gives capacity...

sorry if its really a basic principle that i should know by now but im just not there yet. i had a rudimentary understanding of what i needed to do my build but im only just arriving at the point where i need to finalize my design and purchase what i need.

sorry for the thready hijack too...i can open a new one if necessary