Custom Water Heater, anyone

edco · 06-03-2010, 12:39 AM

Maybe I'm crazy, but I want to install a small hot water heater in my '88 E-150 SMB. Thought it would be nice to have warm water without having to fire up the stove. This is an interesting situation for all you do-it-yourself folks out there. I have extremely limited space to give, so it must fit under the sink (see picture attached). Def a custom job, I'm thinking..on semi-limited funds ($250?). I already detached the town-water supply hose (would never use that anyway), so I have the hot water feed on the sink faucet freed up. I also found a nice little water heater element with a 1" NPT thread for $75 on-line. The website says if you get the 600w/24v model and run it at 12v, then it will only draw 150w...which is 12.5 amps by my calc...correct? I'm thinking this would be a 4 gal. (max) hot water tank, so it shouldn't take much time to heat the water (1/2 hr? just a guesstimate, maybe less?). If I heat the water when the engine is running, I won't have much battery drain, and put in a thermostat in case I forget to shut it off. The bigger problems are squeezing something into the small space next to, or above, or around, the existing 10 gal cold water tank, and figuring out the water flow to feed both cold and hot water to the faucet. I was thinking of a system that automatically fills the hot water tank from the cold water tank, so it never runs dry...a pressurized system would be nice, but not absolutely necessary, unless it IS necessary to accomplish what I have planned. Prob have to have a custom hot water tank welded up? Maybe double-walled so it keeps the water hot and doesn't heat up the compartment too much and melt the nice fake wood veneer? btw, there is only 5 inches between the existing tank and the wall...yoiks.
Anywho, I think it can be done and would be a sweet addition, but I don't have any experience...just a lot of imagination. whaddyathink?

**daveb** · 06-03-2010, 10:28 AM

**WVvan** · 06-03-2010, 12:38 PM

I don't know if you're crazy or not but you have company since I'm planning to do something similar. So I've also researched this problem.

I'm not an engineer so this is pretty much guess work.
If the following rough calculations are right then it would take almost four hours for your heating element to heat up a 4 gal tank.

1 BTU is the energy needed to raise 1lb of water one degree.
1 gal/water ~= 8.3 lbs.
4 gal tank ~= 33.2 lbs
IF the water in the tank is 60 degrees and you want 120 degree hot water then you need to raise it 60 degrees.

60 degrees x 33.2 lbs = 1992 BTUs
1 watt = 3.41 BTU/hr
1992 / 3.41 = 586 watt-hr

If the heating unit puts out 150 watts then
586 watt-hr / 150 watts = 3.9 hours

I'm sure the real calculations are more complex than that. Any engineers in the crowd please jump in at this point.

Another consideration is heating an enclosed container. If you didn't see the whole Mythbusters episode check out this

youtube clip

.

Because of the danger I concluded that a DIY pressurized hot water tank would not be the way to go.

I'm look at a system that uses a espar coolant heater to heat the water. It seems the most energy efficient without having to go to propane. Since the hot water tank isn't pressurized there will have to be a after-tank hot water pump. That's the bare outlines. Haven't started building it yet so don't know if it will work.

edco · 06-07-2010, 12:48 AM

Nice calculation WV, thanks, that'll kill the batteries for sure. that video scares me too, so I'm going to go non-pressurized.
I found your topic on the water heater and bookmarked it so I can get in on the fun! I guess propane is out, the option using the inverter is out (since i don't have one nor plan on getting one...yet), and i'm gonna read all those flatplate discussions (thanks Dave), tho the potential glycol leaks scare me, too.
I did a google search of the espar coolant heater and couldn't figure out what you planned to do with it...says it is for heating the passenger compartment. Am I missing something there? The more I get into this the more I am learning, which is a good thing.

**WVvan** · 06-07-2010, 01:11 PM

Quote:

espar coolant heater ...says it is for heating the passenger compartment.

The espar coolant heater uses a heater core to heat air. I don't see why you couldn't immerse a heater core in a container of water to heat it. This whole system would be to heat around 3 gallons for an external shower. I tend to get pretty crusty after biking or hiking all day so a shower is a big deal for me.
For hot water at the sink I'm leaning towards the system JIMAPAL describes. Of course you'll need an inverter for that.