Can water heater run while towing? Here's why . . .

[profdant139]

I am thinking about installing a water-heater-powered underbelly tank heating system -- several of our members have already done so. A very big and daunting project, but I think it is within my competence.

The advantage of using the water heater to keep the fresh water tank from freezing is that it works even without hookups, while the electric tank heaters don't. (And I can't use my furnace to heat the tanks, both because it uses a lot of power and because there is no way to hook up a duct to the existing furnace.)

But here is my concern: if I am traveling in cold weather (let's say about zero degrees Fahrenheit) all day long, the fresh water tank is going to freeze, even if I enclose and insulate the underbelly (which of course I am going to do). So I would want to run the water heater while in transit, to keep the tank minimally warm.

At last, my question: is that possible? Will it stay lit? My fridge flame used to blow out on the road, until I installed a metal shroud around it. Would I have to do the same thing to the water heater? Is that safe?

Thanks in advance for your advice!

[myredracer]

The Mpemba effect. Interesting phenomena but did you know that water can boil and freeze at the same time? It's called the triple point when under the right conditions, water is in a gaseous, liquid and solid form simultaneously. Simple (not) explanation here.

Seems to me that when and if the WH goes out depends on where it is. It only has to go out once while in transit and you could arrive at the destination to find everything frozen solid and then damage to fix?

I'd be investigating other options, if there are any. Maybe purge the lines and HW heater each time and come up with a way to prevent just the tank from freezing? Maybe if the water is sloshing around it won't freeze at a few degrees below zero like when you let an outside faucet drip/dribble? How long exposed to sub-freezing temps and how much below freezing?

[GordonThree]

profdant139 wrote:
Hmm. Piano, I had not thought of that. Don't want the insides of the pump to melt!

It's not possible for hot water to melt the pump. There's a valid concern that a poorly made pump could contaminate the drinking water.

[profdant139]

Hmm. Piano, I had not thought of that. Don't want the insides of the pump to melt!

[pianotuna]

You need a pump rated for hot potable water.

[GordonThree]

profdant139 wrote:
gary, that would work, except this is a trailer -- no engine.

I am sort of surprised that no one makes an after-market kit that would accomplish what I am trying to do -- to run hot water into the fresh water tank, regulated by a thermostat. There must be a lot of folks who camp in cold weather -- everyone worries about freezing, right?

Gotta keep scheming here . . . there has to be a way to do this.

Almost no one camps in cold weather, just a few of us outliers.

They do sell a product, it's resistance heating pads. They work well.

Like I said in a previous post, it's my opinion extreme cold rv camping requires lots of electricity and propane.

[profdant139]

gary, that would work, except this is a trailer -- no engine.

I am sort of surprised that no one makes an after-market kit that would accomplish what I am trying to do -- to run hot water into the fresh water tank, regulated by a thermostat. There must be a lot of folks who camp in cold weather -- everyone worries about freezing, right?

Gotta keep scheming here . . . there has to be a way to do this.

[garyemunson]

If your water tank sets on a platform, as opposed to being suspended by straps, you could slide a coil of copper tubing under it and pipe it to the engine coolant. Winnebago uses a similar strategy with their "Motor-Aid" water heaters that have an extra pipe welded in that has coolant circulated through it (when you arrive at your destination, the tank is pre-heated). I'm assuming water tank plastic can withstand 200 or so degree heat....

[profdant139]

Thanks for the link -- I am hoping to get info from the manufacturers on the decibel ratings of the smaller units and could then replace my existing pump.

Yes, we seldom use the furnace, but if we are camping in zero degree weather, we will have to have some heat inside the trailer -- probably a Wave 3.

You mention a low pressure circulating pump -- do you mean in addition to the main pump?? Not sure how that would be set up.

[time2roll]

Shurflow, Aquajet and Flojet all make variable speed RV water pumps. I have no experience with these pumps but I speculate they will operate much quieter. Especially if run at a restricted low volume of water. Use a foam pad to mount and use flexible lines placed so they do not rattle against anything.

http://www.campingworld.com/maintain-your-rv/fresh-water/fresh-water-pumps-accessories

Search for some reviews on these items.

A low pressure circulating pump may also provide freeze protection of your pipes. IIRC you camp with minimal use of the furnace so pipe freeze protection is also important.

[GordonThree]

x2 on DrewE's recommendation, just turn off the main pump.

I don't see a way to do this without a solenoid valve, using a secondary pump or not. Once you open the closed-loop system by putting a return line from your hot water heater into your fresh water tank, when your main pump turns on, it's going to lose all its pressure into that return line. Your fixtures won't work, or will work very poorly.

On my system, I have no return line. My little pump just circulates hot water through the water heater, using the existing hot and cold lines. It only keeps the lines from freezing, the tank itself is inside the cabin and is heated by the furnace.

[DrewE]

profdant139 wrote:
OK --time2roll's advice is always pretty darn good, so let's rethink this. It looks like Gordon's ultra quiet brushless pump might be an option -- I am not sure how that would work without triggering my noisy main pump? Or Gordon, did you completely replace your stock pump with the brushless one??

The way I'd do it is to turn the main pump off when using the circulation system, open the circulation valve, and have the quiet little circulation pump switched on and off thermostatically as needed--or, maybe, on a variable timer or something like that, depending on the situation.

Replacing the main pump would be tricky because most of the quiet pumps around are not automatic on-demand pumps with pressure switches and do not incorporate check valves. I suspect many would also have a hard time producing typical household water pressures, being more optimized for low-pressure circulation flow. There are, of course, many different types and styles and sizes of pumps, with corresponding wide variations in pressure and flow rate capacities.

If you used the main pump, you'd have to have some sort of a solenoid valve or similar to control its operation, assuming you didn't want it to run continually...or, I suppose, control the power feed to it while en route.

[profdant139]

OK --time2roll's advice is always pretty darn good, so let's rethink this. It looks like Gordon's ultra quiet brushless pump might be an option -- I am not sure how that would work without triggering my noisy main pump? Or Gordon, did you completely replace your stock pump with the brushless one??

I know there has to be a solution here -- there must be a way to quietly cycle hot water through the fresh water tank intermittently, so as to keep the lines open, using propane (a much better source of heat than electrical resistance).

The "energy density," portability, and availability of propane is so much greater than that in an ordinary battery. Someday, lithium/air batteries will approach the density of hydrocarbons, but we are not there yet.

[time2roll]

Honestly I would try not to go down the resistance heating path if you are on battery power.
Better to mitigate the pump noise.

[profdant139]

piano, the tank is below the floor, and it has never frozen. We have camped many times when the temp gets down to 10 or 15 degrees F., but never below that, and it is almost always in the 30s during the day. My concern is that after many hours of sub-freezing temps, my good luck will run out. I will insulate as much as I can, but insulation does not raise the temp -- it just conserves warmth.

I am currently looking into low-wattage heating pads. They all seem to run off of 120v, so I would use the inverter, I guess.