Salt to fresh water tank to prevent freezing over cold nights?

[Bradeaux]

Hello fellow RV friends,
Very new to RVing as this was our first Summer and LOVING it. Curious about my crazy idea of adding just a little salt to my fresh water tank to resist the lines freezing overnight while up in the Colorado mountains this weekend. It will be subzero overnight but 40-60s during day. It works for boiling pasta water so why not RVs?
Thanks in advance,
Bradeaux

[geotex1]

Ummm... Salt LOWERS the freezing point of water.

[huntindog]

Ummm... Salt LOWERS the freezing point of water.

Which is exactly why this could work..... If one could get past the fact that the FW is then salt water

[John303]

Hello fellow RV friends,
Very new to RVing as this was our first Summer and LOVING it. Curious about my crazy idea of adding just a little salt to my fresh water tank to resist the lines freezing overnight while up in the Colorado mountains this weekend. It will be subzero overnight but 40-60s during day. It works for boiling pasta water so why not RVs?
Thanks in advance,
Bradeaux

Adding salt will in theory lower the freezing point water. The question is how much salt for freezing point depression, how do you rinse it out during the day, and will the salt corrode anything?

https://sciencing.com/calcium-chlori...e-5398442.html seems to say that 10% by weight ratio of salt to water drops the freezing point to -6.4C (20.5F). So say you have 20gallons of water * 8.33lbs = 166.6 lbs. 10% of that is ~17 lbs of salt. That is a lot of salt, not to mention the struggles to get it into the tank by dissolving it in yet more water. Then you have to rinse the tank, flush the lines, and hope the salt did not corrode your pump or any other metal that might be in the plumbing system (hot water heater?). I have no idea what flushing the toilet with salt brine will do to the liquefaction you hope is happening in the black tank.

Best to just run the furnace which I assume heats your basement enough to keep things from freezing. The fireplace, if you have one, is probably not vented to the basement. In addition, you should disconnect the fresh water supply hose from the campsite spigot. If you are boon-docking then that is not a concern. However, boon-docking in freezing weather has its own concerns depending on your rig and equipment.

[geotex1]

Which is exactly why this could work..... If one could get past the fact that the FW is then salt water

I accidentally posted before I finished my point. Yes, salt lowers the freezing point, but you need a tremendous amount of salt per gallon to make a substantial difference. A full tank of water will not freeze in that kind of temperature, but your lines could if not running the furnace.

[ajg617]

Salt water is also a very good electrical conductor which will eat away dissimilar metals very quickly - why I always had to replace the zincs on my rudders and shafts twice a year.

As for boiling spaghetti, adding salt increases the temperature at which water will boil but lowers the specific heat to bring water to the boiling point. So it heats faster but takes longer to boil.

[Petrovsky]

Salt (NaCl) or other salts will have a freezing point depression and boiling point elevation effect. College chemistry. As stated above, you will need quite a bit in order to prevent the freezing. Most of the lines will not freeze as they are located in the main body of the RV and you are heating. However, some lines run through the underbody. You can run some water through the lines at some intervals during the night but if you have outside spray port connections, then this could be an issue. Also as stated above, running the furnace would likely send some hot air in the undercarriage but I couldn't tell you if that would be ideally located or enough.

The salt idea is not a good one especially if you have high blood pressure LOL and likely not good for your hot water tank either (aluminum or not).

I am assuming that when you say subzero you actually mean sub freezing point, i.e. a bit less that 32°F. The water in your holding tank will not freeze and neither would your lines if you are heating your rig during the day at low temp and at comfortable temp overnight, i.e. 50°F during the day and say 65°F to 70°F at night. I have had my rig in - 6°C at night and had no issues with the water lines but most of them ran through the main body. Holding tanks never froze but I did add a bit of RV antifreeze in both grey and black.

However, when you say sub-zero are you saying -5°F. Now that is cold so I don't think your should have water in your lines below grade as they would likely be subject to freezing.

You might keep water in the holding tank but I think that, depending on how many nights you are out there, the temperature in the tank would progressively drop well below freezing and likely not recover during the day. Solution here is to tape the tanks with heating bands. However this will not take care of the lines.

If I were you.....and the temp is well below freezing i.e. much less than 32°F for an extended period....I would winter camp...i.e. have my water supply in 5 gallon jugs in the main cabin. Can still use the toilet but add some RV antifreeze in there prior to the trip. I have camped for about 1 week in my old camper as suggested without any major issues except that I had to re-supply my water a few times. Did my dishes out of camper as well. In other words, used the RV much like I would have used a tent with a potty.

Don't forget to drain your hot water tank as well. I did not use antifreeze in the lines....I just opened up the low point drains and blew out the lines. Camco sells a water line adapter that has a connector for an air compressor on the other end. You really don't need much air pressure to blow out the lines. The issue is the residual water in the water pump and water pump filter. If you water pump is in the main body then you should be fine, if it is in a storage compartment then that is not heated.

Enjoy....it's all about the experience.

[Bradeaux]

Super response John. thank u!

[Bradeaux]

Pierre, great info. Thank you! You are right, i was referring to below 32F. Absolutely love the idea of RV antifreeze in the toilet idea.
Bradeaux

[Tim2542]

If you are living in it, heating it, you’ll be fine even down close to zero. As mentioned, run the furnace (you'll have to below 32° anyway) and use the fresh water tank rather than a hose connection unless you have a heated hose. We spent many nights like this without issue.
If you have a valve installed on the sewer line like many of us do, and your other tank valves leak, like many do, you may see the dump plumbing freeze. Just plan your dumps later in the day when it thaws.