Winterizing RV: Is It Safe To Put RV Antifreeze In Hot Water Heater?

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Winter is taking hold, and the big frosts start to grip. For RV owners, not fully winterizing their recreational vehicle can mean trouble. One of the many questions asked at this time of year is, can you put RV antifreeze in hot water heater?

Draining down your RV and, sometimes, adding RV antifreeze to your hot water heater is recommended to protect your RV plumbing system over winter. The plumbing of a tankless RV water heater also requires the same preparation. Failing to prepare your RV for winter fully can prove costly and mean a new water heater next spring.

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This article discusses winterizing your RV, adding RV antifreeze in a water heater, and how it works in heaters with and without a tank.

Will RV Water Heater Freeze?

Any water left in the water heater tank, its pipes, and the water system can freeze. When the water cools, it contracts until reaching a temperature of 4°C (39.2°F), then slowly expands until it reaches a freezing point. Once the water has frozen, it swells by 9%, taking up more volume than unfrozen water. 

The ice creates pressure in the pipes forcing them to burst.

What Is RV Antifreeze?

RV antifreeze is distinctive from automotive antifreeze, which is toxic and will contaminate RV plumbing systems. RV antifreeze is often referred to as ‘the pink stuff’ since they are primarily pink antifreeze, whereas automotive antifreeze is recognizable by its yellow and green color.

Specifically made for recreational vehicles, it is an essential product to properly winterize your RV. There are many nontoxic RV types of antifreeze on the market today, making them much safer to use in your recreational vehicle’s water tanks and plumbing. 

There are two types of RV antifreeze.

  1. Ethanol
  2. Propylene Glycol

Ethanol (alcohol) Based

It is the most common and cheapest antifreeze and is readily available. While it is safe to put into your RV water lines as directed, reviews state that it leaves an unpleasant taste even after flushing through the RV water system, ready for your first trip.

Suggestions show that ethanol-based RV antifreeze dries out rubber seals, potentially damaging them.

Propylene Glycol 

It is the safest RV antifreeze, not only for yourselves and your RV but also for animals and the environment. It is available in RV shops. Unlike ethanol antifreeze, propylene glycol lubricates your rubber seals and helps to protect them.

Propylene / Ethanol Blend is also a type of antifreeze you see banded around as a possibility. However, it is mainly used as an antifreeze for vehicles and is toxic and unsuitable for RV use.

Can You Put RV Antifreeze in Hot Water Heater?

You can put RV antifreeze in a hot water heater. However, it is often unnecessary and depends on the age of your RV. Newer RVs, less than 12 years old, will likely come with a modern water heater with a bypass valve. 

Having a bypass valve allows you to drain down the RV water heater. If drained properly, there should not be any water remaining to freeze and cause damage.

In older RVs, it is more common to use antifreeze in a hot water heater. Always check with the owner’s manual, as these stipulate whether or not it is safe to add RV antifreeze. Certain brands recommend running RV antifreeze through the water heater and water lines. 

RV Water Heater Tank and How Does it Work?

RV water heaters provide hot water similar to home water heaters. It provides hot water for showering and washing dishes and can be gas or electric-powered.

The water heater in your RV tends to be smaller than the one at home. Your RV holds 6-10 gallons, whereas, at home, it can range from 23 to 60 gallons. 

For this reason, many RVers change their water heater to a tankless water heater to provide an unlimited hot water supply.

You will need to winterize your water heater in whichever model you have.

With Bypass Valve

If your heater has a bypass valve, this is the easiest option to winterize. The primary purpose of the bypass valves is to leave the tank empty. It is faster and cost-effective, as you do not need to use antifreeze in the water heater.

Your RV water heater might have one, two, or three valves. Ensure you have turned all valves open to drain the heater completely. Any small amount of water left in the heater has room for expansion if it freezes. 

Check with your owner’s manual to verify if it is necessary to add antifreeze as a precaution.

Without Bypass Valve

If you do not have a bypass valve, an air compressor can blow the water out of the water lines and system. However, if your RV does not have a bypass valve fitted, adding one is possible and removing the need for antifreeze.

Check Out How to Start & Use an RV Water Heater?:

Disadvantages of Putting RV Antifreeze in Hot Water Heater

There are a few disadvantages of putting RV antifreeze in a water heater, and these include:

  • Expensive. Adding gallons of antifreeze to your water system can be costly every year. 
  • Wasteful. You need to find somewhere like a safe dumping station to get rid of the antifreeze next spring.
  • More work. Come next spring, and more work is involved in flushing through the RV water system to ensure it is clean. 
  • Unpleasant taste. If you have followed the antifreeze instructions, the amount left in your system should not be harmful. It can leave an unpleasant taste. Your system might require a second flush. 
  • Not environmentally friendly. RV antifreeze is okay for humans. However, it can harm animals and the environment. Although, it is becoming easier to find some labeled as non-toxic, biodegradable, and safe. 

Antifreeze Feature on Some Tankless RV Water Heater

Many RV tankless water heaters have an antifreeze feature that detects when the temperature of the water coming through the water lines into the heater drops below 35°F (1.67°C).

There are ceramic heaters inside that fire up when they detect the water temperature dropping and prevent the internal parts from freezing.

Some heaters have a backup in place. If the ceramic heaters fail, an internal sensor detects if the tankless heater is below freezing. If temperatures fall this low, they will automatically turn on and off until temperatures rise above the risk of freezing.

This antifreeze feature is a temporary measure. Long-term use can cause deterioration of the tankless heater.

How To Winterize a Tankless Water Heater Instead

A tankless water heater is also known as an Instant Water Heater, as it supplies RV hot water on demand. So, if a water heater is tankless, does it still need winterizing?

Even if the tankless heater has an antifreeze feature, there is the risk of a power cut, leaving your tankless heater defenseless against the cold. Also, there is the hazard of pipes freezing. If this happens, do not risk using the heater. 

You must allow the tank to thaw and inspect for leaks before switching on the gas or electric power.

You should winterize your tankless water heater and its plumbing system to avoid damage, particularly if you live in an area prone to freezing temperatures. A small amount of water can remain in the system and the water lines leading to and from the heater. The water can freeze, expand and cause damage. Instant heaters are costly to replace.

How To Protect a Tankless Water Heater from Freezing

You can drain your tankless heater manually. However, installing freeze-protection solenoid valves is a great reinforcement to prevent freezing. Their purpose is to automatically drain your tankless heater if there is a power outage. 

They remain in the open position unless there is an electric current to keep them closed.

For your tankless heater to be properly winterized:

  • Turn off the water supply
  • Turn off the temperature control
  • Disconnect the power
  • Drain all the water
  • Remove any drain plugs
  • Blow out the lines with compressed air, checking for the correct psi
  • At this point, you can add antifreeze. However, many feel confident that using compressed air can remove all water and prevent freezing.

Key Takeaway: With all of this in mind, there are still plenty of great reasons to make aftermarket modifications to your car. Just be sure to do your research and understand the potential risks before making any changes.

Protecting Pipes From Frost Damage

Fortunately, external pipes are efficiently protected by pipe insulation, pipe heating cable, or both. You should check the manufacturer’s guidelines for recommendations for installation.

Many pipe heating cables can withstand temperatures of -50°F (-45.5°C). Heating cables and pipe insulation are readily available on the market, easy to use, and relatively cheap.

Related Questions

Is Plumbing Antifreeze the Same As RV Antifreeze?

RV antifreeze is a nontoxic antifreeze specifically for an RV plumbing system. It is not the same as an automotive antifreeze, which is toxic. Their color distinguishes them. RV antifreeze is pink, whereas antifreeze for automotive is yellow/green.

Is It Safe To Put RV Antifreeze in Freshwater Tank?

A hotly debated question. RV antifreeze is nontoxic and should not damage the freshwater tank. Many RV owners prefer to flush the antifreeze throughout the system. Others consider it to have an unpleasant taste and do not like the idea of the chemical in their freshwater.

Can RV Antifreeze Be Used in a Heating System?

Propylene Glycol RV antifreeze is suitable to use in a heating system. However, ethanol antifreeze can dry out rubber seals and cause them to deteriorate. Ethanol is also highly flammable and should not be near pilot flames.

Is an RV Antifreeze Safe To Drink?

Drinking a cupful of RV antifreeze is unsafe. It has a highly unpleasant taste and is harmful in large quantities.

However, if you follow the manufacturer’s guidelines on using RV antifreeze, it is safe to use in the recommended dilution ratios in your RV’s water system.

The Bottom Line

You can put RV antifreeze in a hot water heater if the manufacturer recommends doing so. However, many RV owners are confident that draining down and using an air compressor to force water out of the system is sufficient. 

You have to be careful to use the correct psi. If you over-pressurize the system, you could potentially cause damage to your heater.

It is crucial to winterize your RV correctly. Any water remaining in the system could freeze and damage pipes and heaters.

If you decide to use antifreeze, ensure you use RV antifreeze, not one intended for car use, as this is toxic. RV antifreeze is non-poisonous and recognized by its pink color

RV antifreeze is safe to use in a water tank. However, for many RV users, it is a personal choice not to do so and is considered unnecessary to use in freshwater tanks and heaters.

Taking time to prepare your recreational vehicle for winter entirely is worth the effort. It could save you time and money next spring when you prefer to be hitting the road for fun and adventure.

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Written by William Perry
William was born and raised in the United States and currently lives in Utah. A retired police officer, he is the father of three and grandfather of six. Along with writing, he enjoys traveling, the outdoors, reading and spending time with his grandchildren.
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