Ask Dave: How do I winterize my Aqua-Hot heating system?

Dear Dave,
How do I winterize our RV? It has an Aqua-Hot heating system and heated floors. —Susan, 2022 Tiffin Allegro Bus 40 IP

Dear Susan,
Thanks for the question as this has been a little confusing for owners of traditional RV heating systems and winterizing both the fresh water system and the Aqua-Hot system.

Aqua-Hot has been around for many years. I remember driving by the home office and plant almost 30 years ago every time we went to Longmont, CO, to visit my wife’s parents. It is a hydronic heating system that uses tubing to run a hot liquid to heat exchangers to heat the coach, floor, and even water. It is very similar to the old residential boilers that went to the huge radiators in the room, only much more compact!

How the Aqua-Hot works

The boiler uses Propylene Glycol Boiler Antifreeze and distilled water at a ratio of 35-50% depending on the temperatures you will encounter. This type of antifreeze has a higher boiling point and also lubricates the boiler parts. Aqua-Hot recommends either Camco Boiler Antifreeze or Century products. The Camco is brown in color and the Century is typically green or pink. Check out their boiler antifreeze recommendations here.

The boiler antifreeze is heated to 190 degrees inside the boiler assembly and does not need to be winterized if it is mixed properly and has not diluted. It is recommended to check the level periodically and check the quality with a refractometer rather than the traditional automotive balls in a tube method. These are available through most automobile part stores or on Amazon here.

There should be a chart in your owner’s manual that shows the recommended percent of concentration. The chart below should also work.

You can check and add fluid if needed in the expansion bottle. Make sure the system has been running and check it at a warm temperature, not cold.

The main area that needs to be winterized is the fresh water system that coils through the burner assembly and goes out to all the faucets, heat exchangers, and on-demand systems. They recommend running RV antifreeze (the pink stuff) into the system rather than blowing it out with air as there are several low coil spots that air will not force the fresh water out of.

How to winterize with an Aqua-Hot system

1. Completely drain the fresh water storage tank.
2. Disconnect the domestic water demand pump’s suction line from the fresh water storage tank.
3. Attach an adequate piece of the hose onto the suction side of the domestic water demand pump. (Most RVers purchase a stainless steel braided plumbing hose at a home improvement store long enough to connect to the inlet side of the pump and out to the antifreeze bottles.)
4. Place the opposite end of the hose into an adequate supply of FDA-approved “GRAS” RV Antifreeze and turn on the demand water pump. (“GRAS” stands for “Generally Regarded as Safe.” This is the “Pink Stuff”.)
5. Open and close all interior and exterior water faucets, one at a time, until only pure RV Antifreeze is present. Perform this procedure for both the hot and cold faucets.
6. Turn off the Demand Water pump and remove the hose and reconnect the domestic water demand pump’s suction line to the fresh water storage tank.

Best for two people to do the winterizing

It is best to have two people perform the winterizing, one person to open and close the faucets and such, and the other to ensure the antifreeze bottles are kept full and/or switched so no air gets in the system. Typically it will take 3-4 gallons depending on the washer, dryer and the size of the rig.

Don’t forget the toilet and sprayer, outside showers, and ice maker in the refrigerator if applicable. Do not run RV antifreeze through any filters or the icemaker. Disconnect the filter under the sink and turn off the supply line to the ice maker. Then run it through a few cycles to get all the water out.

If you have a black water tank flush valve, make sure this does not have water in it. You can blow this out with air, or fill a garden hose about 30 feet with RV antifreeze by hand and hook up to a water source. Open the valve and let it run for about three seconds.

Graphics and winterizing procedure provided by Aqua-Hot from the Owner’s Manual.

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Any comments about the Alde heating system?

Dear Dave,
Do you have any experience with the Alde heating system used by nuCamp, Airstream and Roadtrek?

Long story, but based on my personal experience and the multitude of comments on nuCamp forums (haven’t checked any others yet), there are some issues with the Alde heating systems in at least the nuCamp RVs.

Continue reading Calvin’s question and Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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