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!

[Old-Biscuit]

Ultra Heat 12V DC Pad


Therma-Heat 12V DC Pad

[pianotuna]

profdant139,

Has the fresh water tank ever frozen?

Is the tank below the floor of the RV?

profdant139 wrote:
Probably there is no way to know for sure until I try it out in the real world.

[GordonThree]

profdant139 wrote:
Well, I just thought of a show-stopper. Yes, I think I can get this to work, based on what I have read above. And by the way, I have been doing a crude imitation of this project by running a tube from my sink faucet through the hatch to the outdoor shower and out to the fill port for the fresh water tank -- I just turn on the hot water and let it flow for a while. (This has worked (obviously while we are parked!) in temps down to ten degrees above zero Fahrenheit.)

But here is the deal-killer: I realized that if I were to try to use my proposed "automatic" system for boondocking, the water pump would be cycling on and off all night long. Even though I have installed an accumulator and have isolated the pump as much as possible, it would still wake us up from time to time -- the trailer is very quiet at night.

So I don't think I am going to pursue this particular option. My fallback is to check out the various electric tank heater options and see if I can power them with my batteries without draining the batteries too much. I have to figure out the minimum wattage that will still do the job and then calculate my battery capacity and my ability to recharge.

If I install the smallest possible heater under the low point of the fresh water tank (which is the Achilles heel of the whole system) and then install very thick and tight insulation, that might be sufficient.

Probably there is no way to know for sure until I try it out in the real world.

Easy solution (maybe?) don't use your main pump. You don't need (or want) the high pressure/flow from your main pump.

this is what I'm using:
Hot Water Circulation Pump Brushless Motor

another idea I was thinking of, but haven't tried yet, is an inline hot water heater, designed for aquariums. They're typically 200-500 watts, and consist of a plastic pressure vessel with a titanium or glass heater core inside. They max out at around 90F, so that's less energy than the 6-10 gallon propane water heater uses.

[MrWizard]

" Mpemba effect"
learn something new again, thanks got to keep the brain cells working

[profdant139]

Well, I just thought of a show-stopper. Yes, I think I can get this to work, based on what I have read above. And by the way, I have been doing a crude imitation of this project by running a tube from my sink faucet through the hatch to the outdoor shower and out to the fill port for the fresh water tank -- I just turn on the hot water and let it flow for a while. (This has worked (obviously while we are parked!) in temps down to ten degrees above zero Fahrenheit.)

But here is the deal-killer: I realized that if I were to try to use my proposed "automatic" system for boondocking, the water pump would be cycling on and off all night long. Even though I have installed an accumulator and have isolated the pump as much as possible, it would still wake us up from time to time -- the trailer is very quiet at night.

So I don't think I am going to pursue this particular option. My fallback is to check out the various electric tank heater options and see if I can power them with my batteries without draining the batteries too much. I have to figure out the minimum wattage that will still do the job and then calculate my battery capacity and my ability to recharge.

If I install the smallest possible heater under the low point of the fresh water tank (which is the Achilles heel of the whole system) and then install very thick and tight insulation, that might be sufficient.

Probably there is no way to know for sure until I try it out in the real world.

[riven1950]

The Mpemba effect is a real thing, I agree. The key is it is a phenomenon that while it "may" occur it it would likely be under controlled circumstances and usually in a lab, not an RV.

[Lantley]

MrWizard wrote:

Lantley wrote:
Since hot water can freeze faster than cold I think you maybe going down the wrong road.
While the water in the pipes may freeze as long as the tank remains in motion the chances of it freezing are reduced.

HOt water looses heat faster than cold water , because it has heat to loose
this is one of those 'phrases' that is always miss-stated and miss-interperted

it will NOT freeze UP, before an equal size tank of cold water does

it has too loose all that heat before it can began to get cold

he might be talking about an enclosed sealed water heating tube system
not feeding hot water into the fresh water tank ?
convection would keep it circulating, WH would not run constantly
or maybe use a small aquarium/fountain pump
certainly it can be done
my first class A, had a WH with pilot flame, i left it on pilot all the time, except for LP refills, it never blew out

The Mpemba effect is a real phenomenon that is not totally understood, but under certain circumstances the hotter water will freeze first.
Google Mpemba I did not create the pages of info and experiments that will come up.
I agree the circulating warmer can be done. But the more I think about it would it be just as easy to travel with empty tanks. And just fill close to your destination. You would have to travel through extreme cold on a regular basis to make such a system worthwhile.
I'm sure there are those who can benefit from a recirculating fresh tank warmer, but the average RV'er is not out in those conditions.
Nevertheless If the fridge can run while traveling down the road . I imagine a hot water heater can as well which was really the question.

[MrWizard]

Lantley wrote:
Since hot water can freeze faster than cold I think you maybe going down the wrong road.
While the water in the pipes may freeze as long as the tank remains in motion the chances of it freezing are reduced.

HOt water looses heat faster than cold water , because it has heat to loose
this is one of those 'phrases' that is always miss-stated and miss-interperted

it will NOT freeze UP, before an equal size tank of cold water does

it has too loose all that heat before it can began to get cold

he might be talking about an enclosed sealed water heating tube system
not feeding hot water into the fresh water tank ?
convection would keep it circulating, WH would not run constantly
or maybe use a small aquarium/fountain pump
certainly it can be done
my first class A, had a WH with pilot flame, i left it on pilot all the time, except for LP refills, it never blew out

[pianotuna]

The fresh water tank in many RV's is within the heated space.

The issue is the lines--which the makers run along the outside edge of the RV where there is little air circulation unless the furnace fan is running. It is quite possible to have the living quarters at 21 C (70 f) and still have freezing temperatures at the edges of the RV. DAMHIK

[time2roll]

coolmom42 wrote:

time2roll wrote:

profdant139 wrote:
Someone asked for a link to an earlier recirculation project:

Hot water recirculator to prevent freezing of lines

The system was recently upgraded to use the furnace signal to trigger the pump to come on. The more the furnace runs the more the pump runs. No chance to hear the pump while the furnace is running.

So OP will be using both the water heater and furnace while on the road? Sounds a little tricky, but it might work.

It would be a good idea to put a remote temp sensor both inside the RV and water tank area, so temp can be monitored. If the furnace, pump, or water heater fail, things could freeze up.

The link is my system. OP is still in design phase questioning if the water heater will stay lit while in transit. OP wants to use the water heater to keep the fresh water tank from freezing.

[Lantley]

Gordon you bring up a good point. as long as there is plenty of 12 volt power available. I guess it's all doable

[GordonThree]

Lantley wrote:
I like the idea of the circulator pump. But what stop water from freezing within the individual fixtures? Like the toilet valve or kitchen faucet.
Sounds like others have taken this approach so I assume it can be done.
I have never tried to travel with my water heater on in gas mode.

The same thing that keeps those fixtures from freezing normally, that is, you heat your trailer when it's cold.

Circulating hot water keeps lines from freezing that are run in areas that might not be heated, or not adequately heated.

When I travel in very cold weather 10F and below, I have my propane furnace and hot water heater + water circulation system on all the time.

In my opinion, RVing in very cold conditions is not a time to be frugal. I went through about 60lbs of propane and 15 gallons of gasoline alone for a one month winter road trip running heaters and generators to keep things working and free from freeze damage.

[Lantley]

I like the idea of the circulator pump. But what stop water from freezing within the individual fixtures? Like the toilet valve or kitchen faucet.
Sounds like others have taken this approach so I assume it can be done.
I have never tried to travel with my water heater on in gas mode.

[Lantley]

riven1950 wrote:
Hot water does not freeze faster than cold water. It will lose heat at a faster than coldwater. At some point hot water becomes cold water and then the freeze rate is the same, if that makes sense. Put a bucket of 100 degree water and a bucket of 40 degree water outside in freezing weather and see which freezes first.

"The phenomenon of hot water freezing faster than cold water is known as the Mpemba effect, named after Erasto Mpemba, a Tanzanian student who in 1963 was making ice cream as part of a school project.

The students were meant to boil a mixture of cream and sugar, let it cool down, and then put it in the freezer.

Worried about getting a spot in the freezer, Mpemba instead put his mixture in while it was still scorching hot. But after 1.5 hours, his mixture had frozen, while his classmates' mixtures had not.

Intrigued by this phenomenon, he went on to work with physics professor Denis Osborne, and together they were able to replicate the findings and publish a paper in 1969 showing that warm water freezes faster than cold water."

I did not just make this stuff up! Google it while not totally understood it is a real phenomenon.

[BarneyS]

pianotuna wrote:
Hi,

If the belly is enclosed and heated by the furnace then just run it instead?

I use a twin window fan to cause warm cabin air to circulate through the duct work. It draws a whopping 27 watts.

Don,
The OP stated in his opening post "(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.)"
His belly cannot be heated by the furnace as far as I can see according to what he posted.
Barney