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!

[pianotuna]

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.

[coolmom42]

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.

[GordonThree]

I use my hot water heater to keep the water lines from freezing, using a circulation pump. I've never had the heater fail while driving.

Your plan sounds ambitious and fun. Please keep us updated.

[time2roll]

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.

[riven1950]

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.

[Lantley]

Having the water heated may protect the water heater. But unless you circulate the hot water everything else will be unprotected. Circulating the water will require a pump of some sort and electric to power the pump. I can see this being more feasible in a motorized RV vs.a towable.

[profdant139]

Someone asked for a link to an earlier recirculation project:

Hot water recirculator to prevent freezing of lines

My plan (I think) is a little different, and I don't know if it is possible -- the hot water will enter the fresh water tank through a tee in the top tube. The temperature-sensitive valve (see the posting above) will monitor the temp of the water in the tank, perhaps by a sensor in the return line feeding the water heater.

I am hoping (not sure this will work) to "tune" the sensor valve so that it keeps the water in the tank at about 40 degrees, cycling on and off as needed to keep the fresh water system from freezing.

Of course, I will add beefy foam insulation, and of course the bottom will be sealed off with coroplast. That's the easy part. A lot of work, but not technically demanding.

The hard part is figuring out a way to keep the water just warm enough both in transit and while boondocking.

I do not intend to camp in 30 below temps, if I can avoid it --but I do want to do some mid-winter boondocking in the Eastern Sierra, so the heating pads are not going to do the job for me. (I may install them anyway, on the theory that they will come in handy when we have hookups in the winter.)

I suppose I could just monitor my water heater next time we go camping -- turn it on, and maybe put a video camera on my control panel to see if the little "DLI" light comes on (indicating a flame-out). If the water heater can handle the wind while we are driving, I think I can figure out a way to plumb the recirculation system to keep the tank above freezing.

Too bad we are forbidden to own little nuclear reactors, like on a satellite. That would solve everything . . . . . 😉

[time2roll]

All systems can be operated in transit. If the water heater fails for some reason then fix it.

[TenOC]

If you can not find a 12 volt heater pad maybe an inverter, then you can use 120 Volt heater/pad.

[old_guy]

you will have the water heater lame blow out if it is a dsi model be sure you turn it off at the gas station or you might have a shell of an RV after they put the fire out. saw what happens when a frig spark gets done with a MH at the gas station once. burned up a few vehicles and a building and almost a huge propane tank.

[DrewE]

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.

The "hot water freezing faster" is the Mpemba effect, and it's rather uncertain whether or not it's true and under what conditions it may apply if it is true. This is in no small part because it's rather difficult to conduct a controlled experiment.

It is rather clear that hot water generally needs more heat energy removed to freeze than cold water, in as much as hot water must first become cold water before becoming ice. If you add heat to the water at the same rate as it's taken away by the environment while traveling, it won't freeze. This is no less sound than using a heated hose in winter time to keep the hose from freezing.

For what it's worth, my RV water heater does tend to blow out if left on at highway speeds (or perhaps just fail to light at highway speeds), requiring one to cycle the power to get it going again.

[Dutch_12078]

TenOC wrote:
1. The flame on the water heater will blow out.

2. If the underbelly is well insulated, have you thought about installing 1 or 2 12 volt 40 watt light bubes to use as heaters. Two light bubes came with my solar system from Harbor Freight so I assume they have replacement bubes. Or even a small 12 volt heater/fan. While driving down the road the 12 volt batteries will stay charged.

3. If not well insulated the 50 MPH "wind chill" will take a lot of heat from the underbelly.

1. Maybe, but ours has never blown out when we've turned the water heater on 30-45 minutes before arriving at our site.

2. I'd think 12-volt tank heater pads made for the purpose would be a better choice that would more evenly distribute the heat.

3. "Wind chill" does not affect inanimate objects, although wind will increase the heat transfer from the warmer object. It will not though, reduce the temperature below ambient as wind chill will on exposed skin.

[MDKMDK]

I'm going with old biscuit's heater pads, or TenOC's light bulbs and heater fans, but only if you decide that Lantley's "why bother" isn't the answer you like.

I'd try to find some 12V heater pads and a way to power them, instead of running what is effectively a tankless water heater recirculation line from the fresh tank out and back. If I understand what you plan to do?

[Lantley]

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.

[TenOC]

1. The flame on the water heater will blow out.

2. If the underbelly is well insulated, have you thought about installing 1 or 2 12 volt 40 watt light bubes to use as heaters. Two light bubes came with my solar system from Harbor Freight so I assume they have replacement bubes. Or even a small 12 volt heater/fan. While driving down the road the 12 volt batteries will stay charged.

3. If not well insulated the 50 MPH "wind chill" will take a lot of heat from the underbelly.