Professional RV winterization by rig size — travel trailers at the low end, Class A motorhomes at the top. DIY costs $20–$60 in antifreeze and a siphon kit.
KOAWhen to Winterize Your RV in Sammamish, WA
ON TRACK141 days until first 28°F freezeNov 29
Aim to winterize your RV in Sammamish by November 19, roughly a week and a half before the median first 28°F freeze of November 29, which one fall in ten shows up by November 6. The early-odds date runs roughly 23 days ahead of the median, so build in that buffer.
Nov 19Local deadline
Nov 29Median first 28°F
55 days28°F window spread
4 inSnow per season
OUTLOOK
Typical first first 28°F freeze near Nov 29; local deadline about Nov 19. The live 10-day outlook loads here.
Local freeze dates for Sammamish
| Threshold | Early (1-in-10) | Median | Late (9-in-10) |
|---|---|---|---|
| 32°F (light freeze) | Oct 22 | Nov 7 | Dec 1 |
| 28°F (hard freeze) | Nov 6 | Nov 29 | Dec 31 |
| 24°F (severe) | Nov 21 | Dec 18 | Feb 6 |
Bars span the early (1-in-10) to late (9-in-10) window for each freeze threshold; the dot marks the median year. The dashed line is the local prep deadline.
NOAA station: Snoqualmie Falls · 10.6 mi away · 440 ft elevation.
- Sammamish freezes late, but a single early cold snap can still arrive weeks before the median date.
- The 55-day gap between the earliest and latest freeze dates here is wide, so the live outlook matters more than the calendar.
For Sammamish, the nearest NOAA station with freeze data is Snoqualmie Falls, 10.6 miles out at 440 feet. Median first-freeze dates there run 32°F by Nov 7, 28°F by Nov 29, 24°F by Dec 18. The 28°F freeze has come as early as Nov 6 and as late as Dec 31, a 55-day spread. Spring's last 32°F freeze clears around Mar 30. Snowfall averages 4 inches a year, first reaching an inch near December.
The freeze arrives in two steps in Sammamish: 32°F around Nov 7, then a hard 28°F near Nov 29. The 32°F date swings from Oct 22 at its earliest to Dec 1 at its latest, near 40 days. The last spring freeze averages Mar 30 and as late as Apr 21, which sets the safe window for reopening outdoor water and de-winterizing gear. At about 4 inches of snow a year, the freeze — not snow load — is the thing to plan around.
Your rv checklist
- Drain the fresh, gray, and black tanks, then drain the water heater only after it has cooled and lost pressure.
- Bypass the water heater so you do not waste six gallons of antifreeze filling the tank.
- Blow out the lines with a compressor at about 30–40 psi, then pump non-toxic RV antifreeze through every faucet until it runs pink.Helpful gear: RV antifreeze (6-pack) — Recommended pick
- Use a water-pump converter kit to draw antifreeze straight from the jug through the plumbing.Helpful gear: Water pump converter kit — Recommended pick
- Pour a cup of antifreeze into each drain trap and the toilet to protect the seals.
- Fit a blow-out plug at the city-water inlet so you can clear that line too.Helpful gear: Blow-out plug — Recommended pick
- Remove batteries or put them on a maintainer, and store them off a cold concrete floor.
- Cover roof vents, close the propane, and set out traps or deterrents so mice do not move in.
What to have on hand
As an Amazon Associate we may earn from qualifying purchases. Product picks are editorial; links do not change what you pay.
RV antifreeze (6-pack)
Non-toxic pink fluid for the fresh-water plumbing and traps.
Recommended pickWater pump converter kit
Siphon kit that draws antifreeze straight through the pump.
Recommended pickBlow-out plug
Adapter that lets a compressor clear the lines before antifreeze.
Recommended pickHeated fresh-water hose
For anyone staying hooked up through a cold snap.
Recommended pickRV winterization cost & key numbers
Verified national benchmarks; sources open in a new tab (nofollow).
Non-toxic propylene glycol antifreeze a typical rig needs ($5–$10 per gallon); large fifth wheels take 4–5. Add a gallon each for a dishwasher or washer.
RV LifestyleAntifreeze wasted if you skip the water-heater bypass — the tank swallows it before any reaches the plumbing. A bypass kit pays for itself the first season.
CamcoReplacement cost of a freeze-cracked RV water pump; fittings, the toilet valve and the city-water inlet crack first. Most RV policies exclude freeze damage from skipped winterization.
ProgressiveWhat this means locally
Compared with nearby cities, Sammamish's first-freeze date near Nov 29 sits about a week ahead of Redmond (Dec 11) and about a week ahead of Bellevue (Dec 11). Washington's deadlines span Oct 6 to Dec 1 statewide — one date for all of Washington would be off by weeks for Sammamish. Once you know Sammamish's freeze date, use it to shut down your sprinklers and winterize a boat too. Keeping an eye on the rest of the county? The same local math is on our Richland and Seattle pages.
Other winter jobs in Sammamish
Every task below is dated to Sammamish's own freeze and snow normals.
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Frequently asked questions
At what temperature do RV pipes freeze?
An RV's exposed plumbing and thin-walled tanks can begin to freeze once temperatures sit in the mid-20s for a few hours, sooner than a house because there is little insulation around the lines. That is why the winterizing deadline tracks the first 28°F freeze rather than the first light frost.
How much RV antifreeze do I need?
Most travel trailers and motorhomes take about two to three gallons of non-toxic RV antifreeze, and larger rigs more. Bypassing the water heater saves roughly six gallons you would otherwise waste filling the tank. Buy an extra jug; stores sell out once the first freeze warnings hit.
Can I just use my RV furnace instead of winterizing?
Relying on the furnace is risky. A propane run-out, a tripped breaker, or a dead battery during a cold night leaves the plumbing unprotected, and the furnace may not keep the underbelly and bays warm enough anyway. Draining and adding antifreeze is the dependable way to protect the system.
How do I winterize an RV water heater?
Let the tank cool and lose pressure, then drain it and, if fitted, pull the anode rod. Do not add antifreeze to the water heater tank; instead, set the bypass valves so antifreeze skips the tank and fills only the lines. Fresh antifreeze in an unbypassed heater just wastes several gallons.
When is it safe to de-winterize an RV in Sammamish?
Wait until the last spring freeze has passed, which averages near Mar 30 here. De-winterize by flushing the antifreeze from the lines, sanitizing the fresh tank, and checking for leaks before a trip. Reopening too early risks a surprise late freeze on a charged system.
Do I need to winterize an RV stored indoors?
A reliably heated indoor space that stays above freezing protects the plumbing, so full winterizing may not be needed. But an unheated garage or barn can still drop below freezing on a cold night. If you cannot guarantee the space stays warm, winterize to be safe.
How much does it cost to winterize an RV?
Professional service runs $150–$400 depending on rig size — travel trailers at the low end, Class A motorhomes and fifth wheels at the top, plus $15–$50 per add-on like a washing machine or ice maker. DIY costs $20–$60 total: 2–3 gallons of RV antifreeze plus a one-time water pump siphon kit.
What happens if I skip winterizing the RV?
Ice cracks the rigid parts first: the toilet flush valve, the water pump housing ($320–$800 to replace), the city-water inlet and the water heater tank ($500–$1,500 in parts). Hidden cracks often only show once the system is re-pressurized in spring, and most RV insurance policies exclude freeze damage caused by failure to winterize.
RV Winterization: related searches
Searches this guide answers: RV antifreeze how many gallons, water heater bypass kit, blow out RV lines with air, and RV winterization service near me.
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Data: NOAA 1991–2020 normals via Snoqualmie Falls, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 25, 2026.