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!

So, your plan is to circulate water out of the potable tank thru thr water heater? I assume your plannjng on some sort of bypass so your not trying to use hot water all the time.Can it be done? Sure, anything is possible. Will the WH keep running and not blow out going down the road? Maybe, maybe not. Likely it will blow out, or burn a lot of propane trying to get all that water hot.

"or burn a lot of propane trying to get all that water hot."That would be my concern. Its not stayin in an insulated tank so isn't it going to be running non-stop?

Fridge flame blew out cause of airflow thru lower access/vent cover....lots of airflowWater heater.....outside door/panel is fairly enclosed so flame should stay lit/relight as neededIssue......Water going to tank will be 130*F/140*F (depending on which brand) and then once all the water is heated it will be HOT water in your fresh water tankYou mentioned 'others have done these'-----what/how did they do it???They do make DC Tank Heater Pads. Easier to run larger DC Charge line from truck to camper battery to maintain camper battery drain

I think its a good idea you could install a adjustable thermostat, no need for 130 deg water. don,t think it,ll blow out you,ll have to test that.

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.

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

48 Replies

myredracer
Explorer II
Mar 30, 2018
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
Explorer
Mar 25, 2018
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
Explorer II
Mar 25, 2018
Hmm. Piano, I had not thought of that. Don't want the insides of the pump to melt!
pianotuna
Nomad III
Mar 24, 2018
You need a pump rated for hot potable water.
GordonThree
Explorer
Mar 24, 2018
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
Explorer II
Mar 24, 2018
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
Explorer II
Mar 24, 2018
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
Explorer II
Mar 23, 2018
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
Nomad
Mar 22, 2018
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
Explorer
Mar 22, 2018
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.