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Winterizing - water system

The primary objective in decommissioning potable and cooling water systems is to prevent damaging freeze-ups in colder climates. The surest way to do this is to completely drain all water from the systems. If that isn't possible, the addition of non-toxic antifreeze is the safest and most reliable method of prevention.

Unfortunately, the level of protection offered by antifreeze solutions is often misunderstood. The quoted level of protection - "down to -50 F" - is derived from residential construction standards and is intended to mean that copper pipes will burst when the antifreeze in them reaches that temperature. The "-50 F" is a failure point, not a protection point.

The danger is that the plastic pipes, filter housings and pump bodies in marine use will be destroyed long before that level, so it's important to choose the type and strength of the antifreeze solution. You must assume that some water will remain in the system, which will dilute the antifreeze and raise its freeze point. The extra cost (about double) of "-100 F" antifreeze can be inexpensive insurance.

Here are some important points:

  • Run the faucets to drain the water from the tank. If you have an accumulator tank, drain it before you start. Drain as much of the water from the system as possible before adding antifreeze. Make sure the boat is as level as possible so tanks will drain completely.
  • Make sure the hot water heater is off - the elements must be in water or they will burn out - and drain that. Water heaters are usually equipped with a check valve in the water inlet that prevents draining back into the system. Most are equipped with a separate outlet that allows complete drainage. When the water tank is empty, pour in non-toxic antifreeze. It should take about three to five gallons. If possible, bypass the hot water heater to use less antifreeze.
  • Pump antifreeze through every outlet on the boat to ensure each line is protected. Once the color of the flow indicates antifreeze is coming through, redirect it to a bucket. The overflow can be recycled back through to reduce the amount of antifreeze required, or used to protect deck drain plumbing and areas where water remains in the bilge and holding tanks.
  • Don't forget the shower and the head if it is flushed by fresh water. If the head is flushed with raw water, find the seacock and remove the hose, then put the hose into a container of non-toxic antifreeze and flush until it comes through. The water system should be finished. Put all hoses and fittings back so you won't forget them in the spring. Don't neglect the shower sump. It should be cleaned with a bleach solution to cut soap scum and kill bacteria, then filled with antifreeze that can be run through to protect its pump and drain system. (Click here to read more on proper cleaning below to avoid mold and mildew.)
  • Operate and lubricate seacocks.
  • Flush saltwater washdowns and bait well systems to remove scale and run with non-toxic antifreeze.
Return to The Soundings Boat Shop Complete Guide to Winterizing.

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