12v DC Water Pre Heater ???

[Rbertalotto]

Over at "Surplus Center" they have a 800w / 12V water heater for $20

Would this have value as a preheater at the sink or shower level to get hot water faster?

http://www.surpluscenter.com/Electr...ical/800-WATT-12-VDC-WATER-HEATER-11-3439.axd

12 VDC WATER HEATER
New, THERMO KING model 12-923 water heating assembly. Made as part of a winterization kit for heavy duty trucks. Includes mounting feet, connection box and hose barbs.

SPECIFICATIONS
Voltage 12 DC
Wattage 800
Ports 1 " NPT
Hose Size 3/4" ID
Size 16" x 4" x 4-1/2"
Shpg. 6 lbs.

 

[broken1]

Cool concept but

800 watts (advertised) at 12V would be 66.6 amps. That's a lot. Heavy wiring and a good sized battery bank would be necessary for any appreciable usage time, and then a robust charging system to charge it back up after usage...

The Vendor states. in the Q&A section "This is strictly a heating component but it is designed to be a system that has fluid circulating all the time." so you would need to trigger it off of the pump system pushing water so it didn't burn out.

All that being said I wonder, at only 800 watts, how much of a temperature delta you would get at faucet or shower flow rates given the size... my home water heater is 240-volt and uses around 4,500 watts. When it's been emptied the temperature delta between inlet and outlet is pretty weak...

 

[dwh]

Nifty. Looks to be made to heat up engine coolant. Depending on pump speed/volume, it might not keep the water in the heater area long enough to do much. Over time, cycling repeatedly through an engine, it would warm it up, but just moving water through it once might not do a lot to raise the temperature of the water.

I doubt it would do much trying to use it as a jury-rigged "instant-hot".

And... 800w / 12v = 67a.

Still, for that price, it would certainly be worth getting one to play with.

 

[dwh]

broken1 beat me to it.

 

[Rbertalotto]

Was thinking as only a pre-heater / booster until the hot water from the main tank gets to the faucet. Would only need to be on a few seconds as long as it heated the water fast enough. Would save a huge amount of water if it worked. Lots of folks run the hot water until the "hot" arrives. Wasting precious water in a camper.

 

[dwh]

In the large mansions in Beverly Hills, it's pretty common to run the hot water as a loop with a circulating pump, and then T off the loop to feed the faucet through a short run of pipe. That keeps hot water within inches of the faucet at all times.

They aren't trying to save water of course, but simply don't want to wait for hot water to travel a hundred feet from the water heater to the master bath. Saving water is a side benefit.

A similar scheme would work in a camper, but would it save enough water to bother with it?

 

[anickode]

If my math is right (which it probably isn't), 800 Watts would only result in about a 5 degree increase in temp with a 1 gallon per minute flow. Even so, a nearly 70 amp load would take a serious battery bank, otherwise you'd need to be running the engine to supply the power, in which case, you might as Well run a water to water heat exchanger off the engine coolant and have an unlimited flow of hot hot water.

I remember seeing an electric on-demand household water rated to supply 2 points of use continuously... so in house terms That's about 5 gpm which is significantly higher than camper showers, but still. It required THREE sixty amp 2-pole breakers. That's 43,000 Watts, or 3600 amps at 12v. So divide by 5 to figure a 1gpm camper shower flow, and you get 8,600 Watts, or roughly 720 amps.

Might make a good washer fluid heater/windshield deicer...?

 

[AndrewP]

Too many amps for a small mobile system. And, not enough heat in the water.

Much better to have a coolant heat exchanger and plenty of hot water without running down your battery (bank).

A good camping system should recycle the water until "hot enough" is achieved.

I can't see this working for our little community unless unlimited shore power was available.

 

[unseenone]

If one was desperate for hot water, probably an RV or Boat water heater would do quite nicely. I don't know about RV ones, but boat ones use the heat from the engine coolant to make hot water while the engine is running. It's pretty efficient, also operates on A/C when it's available.

I looked at this for about 5 minutes, and quickly decided more engineering was required than I was willing to do. It would probably continue to heat the water, hotter and hotter to a point, but the pumps and other messing around seems like too much work when you can get something that will do it. It would be ok for a "fun" project for someone that had the time.

 

[KevinsOffroad]

I realize this wasn't part of the original question, however, there's another way to skin the cat:

http://amzn.com/B000TXOJQ4
or
http://amzn.com/B001J4AU2E