FrostList

When to Winterize Your Boat in Concord, NH

ON TRACK94 days until first 28°F freezeOct 13

Freeze protection for a Concord boat keys off the first 28°F freeze, which averages October 13, so haul out and winterize by October 6 to beat it. The early-to-late range spans roughly 29 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first first 28°F freeze near Oct 13; local deadline about Oct 6. The live 10-day outlook loads here.

Local freeze dates for Concord

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 21Oct 3Oct 16
28°F (hard freeze)Oct 1Oct 13Oct 30
24°F (severe)Oct 10Oct 25Nov 9

NOAA station: Concord Muni AP · 2.0 mi away · 346 ft elevation.

Numbers for Concord come from Concord Muni AP, 2.0 miles away at 346 feet, where the medians fall 32°F by Oct 3, 28°F by Oct 13, 24°F by Oct 25. The 28°F freeze has come as early as Oct 1 and as late as Oct 30, a 29-day spread. Spring's last 32°F freeze clears around May 8. Snowfall averages 68 inches a year, first reaching an inch near November.

Expect the first frost near Oct 3 in Concord and the first hard freeze by about Oct 13. The 32°F date swings from Sep 21 at its earliest to Oct 16 at its latest, near 25 days. The last spring freeze averages May 8 and as late as May 22, which sets the safe window for reopening outdoor water and de-winterizing gear. Roughly 68 inches of snow fall in an average year, so a clear roof edge and a running snow blower matter as much as the freeze itself.

Your boat checklist

  1. Change the engine oil and filter while the motor is warm so contaminants leave with the old oil.
  2. Run the engine on antifreeze until pink fluid reaches the outlet, protecting the block and manifolds.
    Helpful gear: Marine antifreeze — Recommended pick
  3. Fog the cylinders with fogging oil as the engine runs down to coat internal parts against corrosion.
    Helpful gear: Fogging oil — Recommended pick
  4. Top off the fuel tank and add stabilizer to limit condensation and protect ethanol-blend fuel.
    Helpful gear: Marine fuel stabilizer — Recommended pick
  5. Drain the raw-water system, the livewell, and any washdown lines that can trap water.
  6. Remove the battery, charge it fully, and keep it on a maintainer over the layup.
    Helpful gear: Battery maintainer — Recommended pick
  7. Support the cover so snow and rain shed off, and leave vents so the interior can breathe.
  8. For an inboard or sterndrive, follow the manual closely — those blocks are the ones freeze claims hit hardest.

What to have on hand

Marine antifreeze
Propylene-glycol fluid rated for engine blocks and systems.
Recommended pick
Marine fuel stabilizer
Additive that protects ethanol-blend fuel over the layup.
Recommended pick
Fogging oil
Spray that coats cylinders against corrosion in storage.
Recommended pick
Battery maintainer
Keeps the cranking battery topped off on the trailer.
Recommended pick

What this means locally

Against its neighbors, Concord (first freeze Oct 13) runs about a week ahead of Manchester (Oct 24) and about a week ahead of Nashua (Oct 24). Across New Hampshire, local prep deadlines in our data range from Oct 6 to Oct 17, so a statewide rule of thumb would miss Concord by weeks. In Concord, that same cold is your cue to winterize an RV and store a motorcycle.

Other winter jobs in Concord

Every task below is dated to Concord's own freeze and snow normals.

Sprinklers → Oct 3Frozen pipes → Sep 21Ice dams → Oct 16Car battery → Oct 13Snow blower → Oct 25Sump pump → May 8RV → Oct 3Motorcycle → Oct 3

See the full Concord winter checklist, in order →

Frequently asked questions

At what temperature does a boat engine block crack?
Trapped water in an engine block or manifold can freeze and crack the casting once temperatures fall below 32°F and stay there long enough. Inboard and sterndrive blocks hold the most water and are the most vulnerable. Draining fully and adding antifreeze before the first hard freeze near Oct 13 is the protection.
Do outboards need winterizing?
Yes. An outboard should be drained so no water sits in the powerhead or lower unit, and the fuel system stabilized. Outboards self-drain better than inboards when tilted down, but fogging the cylinders and changing the gear oil are still part of a proper layup.
Fogging oil: is it necessary?
Fogging coats the cylinder walls and internal parts with a film that resists corrosion during months of storage. On engines that sit all winter it is cheap insurance against rust, especially in humid or coastal storage. Follow your engine maker's guidance on how to apply it.
How much does boat winterization cost?
A professional winterization varies with engine type and boat size, and inboards cost more than a simple outboard. Doing it yourself costs mainly antifreeze, oil, and fogging oil. Either way, the bill is far smaller than repairing a cracked block, which is the failure winterizing prevents.
Do boats in NH really need winterizing?
If temperatures reach freezing where the boat is stored, yes. Freeze claims are common in milder states precisely because owners assume they are safe and skip the step, then a rare cold snap cracks a block. Check the local freeze dates above and protect the engine before the first hard freeze.
When should I de-winterize my boat?
De-winterize in spring once the risk of a hard freeze has passed for your area. Reconnect and charge the battery, replace drain plugs, check hoses and clamps, and inspect the fuel system before the first launch. Reopening too early leaves the block exposed to a late cold snap.

Data: NOAA 1991–2020 normals via Concord Muni AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.