Build my own water heater?

[RVtrek]

So I can start this post with this: I might be crazy.

I would really like to build my own water heater instead of buying one.  Because I'm doing an all-electric build, it's going to be an electric water heater.  I've found a wonderful little 48v DC water heater and all I need now is a tank.  (And yes, I'm building a 48v-based system.)

My question is this: Has anyone taken a standard RV-style water tank and pressurized it?  I'm not looking at any kind of crazy pressures, I'll be using a standard RV water pump and it'll never be hooked up to city water.

Everything I see in the descriptions of regular types of water tanks say they are not designed for pressurized use.  And the only style hot water tanks I'm finding seem to pretty much be cylindrical contraptions with steel bodies that look like they can take pretty good amounts of pressure.  Sure, I can buy one of the cylinder-based tanks and run it off of 120v via the inverter, but I'd really love to build my own tank and have it make better use of space and be more efficient.

Is the 45psi or so that an RV water pump puts out really that damaging to potential hot water tanks that are made out of plastic?  Has anyone here ever built their own hot water tank?

 

[tx2sturgis]

It's funny, I just posted about this over on YT...

That little multi-voltage element with built-in thermostat you linked to is interesting.

But why not just install a small point-of-use water heater? Yes, its a cylinder (or sometimes oval) but you had mentioned earlier your trailer is gonna be a large size so a few cubic inches of unused space seems irrelevant.

Power it with AC (or DC) and not have to worry about a plastic tank failing from the heat...

 

[RVtrek]

But why not just install a small point-of-use water heater? Yes, its a cylinder (or sometimes oval) but you had mentioned earlier your trailer is gonna be a large size so a few cubic inches of unused space seems irrelevant.

Power it with AC (or DC) and not have to worry about a plastic tank failing from the heat...

Yes, I certainly can use the point-of-use water heater, either a 6 or 10 gallon, something like that.  But I'd like to mount my custom water heater next to my holding tanks, completely out of the way.  It also gives me more cabinet space that way too, which is always a good thing.  I probably will go that route, but I figured I'd see if anyone as crazy as me has actually tried building their own tank before.

 

[mr_elijah_gardner]

If your going all electric why not just use an electric instant hot water heater. I saw a used one on CL the other day for $60. Could probably find a new one on eBay cheap to. 

You would have all the hot water you want. Plus you'd have a system that isn't going to fail as easy as your homemade setup. I'm not saying you couldn't build a good one but there are probably things your not thinking of and it would probably take several attempts. The cost and time may quickly exceede  buying something

 

[tx2sturgis]

Yes, I certainly can use the point-of-use water heater, either a 6 or 10 gallon, something like that. 

I was actually referring to a SMALL point-of-use heater...something like 2.5 gallons. Heats very quickly, and most of us when camping can make use of that much and be done with it, the water will be cold again, no waste, till the next time we need it. They take about an hour or less to heat up.

On mine, I had a mechanical timer so that it would heat for about 45 minutes, if I wandered off or something, it would not be left on.

 

[RVtrek]

If your going all electric why not just use an electric instant hot water heater. I saw a used one on CL the other day for $60. Could probably find a new one on eBay cheap to. 

Any decent tankless hot water heater is going to draw at least 5,000 watts, usually on a 240v A/C system.  That's more power than I can create and I don't want to buy another inverter just to run a tankless water heater.  It's easier to just get a point-of-use water heater instead.

 

[RVtrek]

I was actually referring to a SMALL point-of-use heater...something like 2.5 gallons.

Wow, that's pretty tiny.  Right now I have a 6-gallon water heater in my truck camper, and it seems to be enough for me to take brief navy-style showers.  I don't really want to go smaller than that system, and I don't really see a need to.  I'm going to have enough solar (about 1,500 watts) and battery capacity (20kwh usable) that the difference between a 2.5 and 10 gallon hot water heater tanks isn't really that big of a deal.

 

[mr_elijah_gardner]

Any decent tankless hot water heater is going to draw at least 5,000 watts, usually on a 240v A/C system.  That's more power than I can create and I don't want to buy another inverter just to run a tankless water heater.  It's easier to just get a point-of-use water heater instead.

That's a good point. I missed where you said you were still running batteries. I assumed you were doing your build around having access to shore power.

 

[Trebor English]

My question is this: Has anyone taken a standard RV-style water tank and pressurized it? 

To hold pressure it must be round.  Large flat sides will require a lot more material (steel) to hold the pressure.  It's possible, not practical.

 

[Weight]

I would not keep hot water in a plastic tank. Get a small water heater and convert it to DC.

 

[RVtrek]

I would not keep hot water in a plastic tank. Get a small water heater and convert it to DC.

Yep, I think that's pretty much the plan.  I think I'm going to run it on AC until the element dies for whatever reason and when that happens, I swap out the components and run it on DC.  No sense in throwing away perfectly good (AC) heating elements right away.

 

[tx2sturgis]

Just FYI on electric water heaters:

You can buy and install lower power elements, and you can even use elements designed for 240v on a 120v circuit...but NOT the other way around.

The 240v elements will work at much lower wattage (about 1/4th) on 120v and last practically forever.

Since the smaller elements can be bought for $10 to $20 each, it's not expensive to get exactly what you want.

Suppose you wanted a 500 watt element for 120v. You cant find one at the local store but they DO have a 240v element rated at 2000 watts. Assuming the element is not too long for the limited dimensions of a smaller tank, electrically it will work fine on 120v. It will of course take longer to heat up the water, but if you are boondocking on batteries and solar, it might be more 'inverter friendly'.

Of course a generator or shore power could supply more current so probably not an issue in that case.

 

[jimindenver]

My water heater is pressurized by my water pump or the tap when I have hook ups. (it happens) Personally I would find a used RV water heater and add a $100 Hott rod conversion kit. The 6 gallon size uses 450w/120v and takes two hours from cold to 150 F.

 

[CityWoman]

I'm a total newbie not on the road yet, but I've been reading a little about the kinds of water heaters that use the vehicle's coolant system, run through a salt-filled box that is inside the water tank where it heats the water. Isotemp is the name of one, but I bet there is a way to DIY. I find the concept pretty interesting, and I don't know if it would work for you or your vehicle, but I believe that then you wouldn't have to worry about drawing power from your system.

 

[highdesertranger]

Jim beat me to it. some RV water heaters already have the electrical element built in, just swap in a 48v element. BTW if you build your own don't forget a pressure relief valve. highdesertranger

 

[karl]

I'm a total newbie not on the road yet, but I've been reading a little about the kinds of water heaters that use the vehicle's coolant system, run through a salt-filled box that is inside the water tank where it heats the water. Isotemp is the name of one, but I bet there is a way to DIY.

I have built 2 units that plumbed from tee's in heater lines through an automotive heater core in a tank for the purpose of storing heat to later be radiated into my living space ( lots of cold weather travel), one was 20 gallons of storage under the bed in a standard van, the other 40 gal in a step van.
They did the job until I could afford a furnace and replaced them.(easier control, less overheating of the bed/space, less weight)

I did make a 10 gallon water heater by using a (new) aluminum fuel cell and sitting it on an insulated base with a coil of copper tubing plumbed and valved into the engines heater lines. The tank sat directly on the copper coil so there was no chance of antifreeze contaminating the water. The only tank modifications were removing the foam inside and adding an overflow/expansion vent to the top since I chose not to pressurize it.
It worked perfectly until the weld on the entire seam of one side failed- cheap chinese heliarcing.....

Have considered doing it again ,but using an old 5 gal stainless dairy milking machine.......

 

[Spaceman Spiff]

 . . . BTW if you build your own don't forget a pressure relief valve.  highdesertranger

And a sacrificial cathode.