Updated 11/23
I am often asked about using RV antifreeze to winterize the water system in an RV. There are questions about what it is, how to use it if necessary, and if it is safe.
First and foremost, RV/Marine antifreeze for plumbing systems is not the same as automotive or boiler antifreeze. They are not interchangeable. RV antifreeze is non-toxic, unlike its automotive counterpart.
RV antifreeze is made primarily of propylene glycol, an alcohol that is a common food additive. It is a viscous liquid with a slightly sweet taste in its raw form. RV antifreeze will actually freeze, but it will not hydraulically expand and cause damage when it thaws. When above its freeze limit, it remains slightly slushy.
RV antifreeze comes in two basic types based on PEX pipe burst temperature: -50F and -100F, although StarBrite makes a -200F version that can be diluted as needed. A concentrated version is also available, mixed with water to reach the desired volume.
The product is usually pink, but peach, orange, and purple are out there. It will be marked as RV antifreeze and will never be green. It should also have a peppermint-like smell.
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Safety
RV antifreeze, as stated before, is alcohol and a food additive and is considered as generally safe by the US Government. That said, I would not recommend using it as a cocktail, as it tastes horrible… don’t ask me how I know that. Suffice to say that once your RVs water system is flushed with water in the spring, any residual will be harmless, but the smell of peppermint and the foaming of the product coming out of the faucet will be an annoyance, so making certain every part of your plumbing system is flushed is important.
Propylene glycol does have bactericidal effects at various concentrations above 50-percent according to the National Institutes of Health. That said, as the concentrations in RV antifreeze vary with the additives, it is still recommended that the fresh water system be sanitized as recommended by the Public Health Service. The procedure for this is outlined in your RV’s owner’s manual, and will be the subject of a future article.
Do I need to use RV antifreeze?
This is a valid question, as not all systems require using antifreeze, however it is recommended for all water systems.
First, the antifreeze displaces any remaining water. When a system is blown out, some liquid water remains in the pipes due to surface tension, and will settle down into lower parts of the system over time. If it collects in one spot it can cause freeze damage.
Second, some valves on toilets, ice makers, and other appliances and fixtures can hold water even if they are blown out. Water pump screens are notorious for this. Antifreeze will, again, displace the water.
Third, when the piping is left open to air, the remaining moisture can combine with airborne spores, leading to mold, mildew, and algae growth in the system. The RV antifreeze will not allow anything to grow in the system. The fresh water and water heater tanks in the system have enough airflow when left open so as not to encourage growth over the winter, but if they are stored empty in hot weather, they should be resealed.
Which antifreeze should I use?
There is one overarching difference between potable water system antifreezes and that is burst temperature protection. It has to protect for colder conditions than your RV will experience while in storage. From a price standpoint, a recent Google search found RV antifreeze prices starting at $2.99 US per gallon.
Is there anywhere in an RV plumbing system where I must use antifreeze?
Yes! If your RV is equipped with a hydronic heating system like the Aqua Hot, your RV plumbing must be winterized with RV antifreeze. The copper coils for domestic hot water run through the boiler unit, holding water in the bottom parts of the coils even when blown out with compressed air. This leads to freezing and bursting, which will destroy the unit, requiring complete replacement.
Is there any point in the system that should not have RV antifreeze?
Yes. As a rule, tank water heaters should be drained and bypassed, leaving the drain plug (anode rod in Suburban units) out. Antifreeze that gets in the tank can lead to taste/smell issues that are hard to flush out.
Some instant water heaters like the Truma AquaGo also don’t require antifreeze, although you should always follow the manufacturer's recommendations. Compressed air should also not be used on these units because component damage can occur.
Fresh water holding tanks also do not need, nor should they get, antifreeze. It is a waste of product and also can lead to taste issues. Drain the tank and leave the drain open.
How do I dispose of used RV antifreeze?
Due to its generally safe designation, there are no US EPA regulations regarding disposal of RV antifreeze, however some states do regulate its disposal, so follow the local guidelines.
From a general standpoint, it can be flushed into your holding tanks and be disposed of the next time you dump. Any small amount flushed from exterior faucets or low point drains is harmless, but can be collected and disposed of down your toilet drain if you choose.
How long can I keep RV antifreeze around, and can I reuse it?
If the bottles remain sealed, some brands suggest there is no expiration date on their products, however once opened are subject to eventual degradation. Obviously their effectiveness is decreased when diluted with water. It is not recommended to reuse RV antifreeze for this reason.
In summary, it is best to use RV antifreeze to winterize your RV because of the various benefits it provides and its overall safety.