Winterizing Checklist — RV & Boat
The steps that actually cause damage if you skip them, how much antifreeze the water system needs, and whether the battery will survive.
Winterizing checklist
Steps marked ⚠ cause damage if skipped. The others cost you comfort or money later. Nothing here is saved — this is a pass to work through, not a record.
How much antifreeze
Blowing the lines out
Use no more than 50 psi, and 40 is plenty. Above that, fittings and the pump split — and the failure does not show itself until you pressurise the system in spring, by which point the damage has had all winter to sit there. Most compressors will happily deliver three times that, so set the regulator before you connect anything.
Will the battery survive?
| Charge | Specific gravity | Freezes at |
|---|---|---|
| 100% | 1.265 | -71°F |
| 75% | 1.225 | -35°F |
| 50% | 1.190 | -10°F |
| 25% | 1.155 | 5°F |
| 0% | 1.120 | 20°F |
The electrolyte in a discharged battery is closer to plain water, and plain water freezes. That is the whole mechanism — and it means a flat battery is destroyed by a mild frost while the identical battery, fully charged, is safe to seventy below.
Things worth knowing
- Use RV antifreeze — propylene glycol, dyed pink — in anything that touches drinking water. Automotive antifreeze is ethylene glycol and it is toxic; the two are not interchangeable and the colour is the only obvious difference.
- Diluted antifreeze freezes. Any water left in a line before you add antifreeze reduces the protection, which is why draining comes first and is not optional.
- Bypass the water heater. Six gallons of antifreeze in a tank that did not need it is money out and a flushing job in spring.
- Never exceed about 50 psi when blowing lines out. Fittings and the pump itself split, and the failure will not show up until you pressurise the system next season.
- A discharged lead-acid battery freezes at around 20°F and is destroyed by it. The same battery fully charged is safe to about −70. Charge it before you store it, and keep it charged.
- Write down what you did and where the bypass valves are. Next autumn is eleven months away and you will not remember.
How to use
- Pick RV or boat and work down the list — ⚠ marks the steps that cause damage.
- Use the antifreeze calculator, and check whether your water heater is bypassed.
- Set the battery charge and expected low to see whether it will freeze.
Frequently asked questions
How much RV antifreeze do I need?
About two to three gallons for the lines and traps if the water heater is bypassed. If it is not, add the heater’s whole capacity — six gallons of antifreeze filling a tank that did not need it, and a flushing job in spring.
Can I use car antifreeze?
No. Automotive antifreeze is ethylene glycol and it is toxic. Anything touching a drinking water system needs RV antifreeze, which is propylene glycol and dyed pink. The colour is the most obvious difference and it matters.
What pressure should I blow the lines out at?
No more than 50 psi, and 40 is plenty. Above that, fittings and the pump split — and the failure does not reveal itself until you pressurise the system in spring. Most compressors deliver three times that, so set the regulator first.
At what temperature does an RV battery freeze?
It depends entirely on charge. A flat lead-acid battery freezes at around 20°F and is destroyed by it; the same battery fully charged is safe to about −70°F. The electrolyte in a discharged battery is closer to plain water, and plain water freezes.
Do I need to drain before adding antifreeze?
Yes, and it is not optional. Antifreeze poured into a system still holding water is diluted, and diluted antifreeze freezes. That is why draining comes first on the list.
What is the most expensive thing to skip?
Rodents and roof seams. Rodent damage to wiring is the costliest winter problem there is and it is entirely preventable, and a roof seam that starts leaking in November has all winter to work on it.
What sinks boats over winter?
The drain plug left in, and a flat tarp instead of a supported cover. Rain and snowmelt collect, then freeze, and a cover without a frame ponds water until it tears or collapses.
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