How to Prevent Frozen Pipes in Portsmouth, NH
To prevent frozen pipes in Portsmouth, NH, keep heat reaching exposed plumbing, stop cold drafts, protect outdoor connections and know where your main shutoff is before winter arrives. This guide covers preparation, cold-snap habits and the safe next steps if a line freezes anyway.
Most of the work happens in autumn. A little preparation is far easier than drying out a ceiling in February.
Call (844) 442-1700 if a pipe has already frozen or burst and you need to reach a local plumbing provider.
How to Reduce Frozen-Pipe Risk in Portsmouth
Frozen pipes are mostly a problem of cold air reaching water that is not moving. Reduce cold exposure, keep warmth near the pipes and drain lines you do not need.
The core steps are simple:
- Find and label your main water shutoff.
- Seal drafts near pipes in basements, crawl spaces and garages.
- Insulate exposed pipes in unheated areas.
- Shut off and drain outdoor faucets and hoses.
- Keep the heat on, even when the building is empty.
- Make a plan for trips and vacant periods.
The City of Portsmouth has published winter guidance on owners’ responsibilities and freeze prevention. Its 2018 notice links to that guidance.
Source: City of Portsmouth — Protect Your Pipes This Winter, January 3, 2018.
Why Pipes Freeze in Cold Weather
Water expands as it freezes. In a closed pipe, that expansion builds pressure between the ice and a closed faucet or valve.
The pipe often splits where pressure builds, not exactly where the ice formed. That is why a burst can appear some distance from the coldest spot.
Wind makes things worse. Cold air blowing through a gap can freeze a pipe in a room that otherwise feels acceptable.
Which Plumbing Runs Are Most Exposed
Pipes freeze where cold air reaches them and warm air does not. The location matters more than the age of the house.
| Location | Risk | Prevention |
|---|---|---|
| Outdoor faucets and hose bibs | Direct exposure; trapped water in the line | Shut off the inside valve, drain, remove hoses |
| Unheated crawl spaces | Cold air and wind under the floor | Seal vents in winter where appropriate, insulate pipes |
| Exterior walls | Pipes near cold sheathing | Seal drafts, keep cabinets warm, consider rerouting later |
| Unheated garages | Pipes and supply lines near doors | Keep doors closed, insulate lines |
| Basement rim joist area | Air leaks where pipes enter | Seal gaps around penetrations |
| Kitchen and bath sinks on outside walls | Cold air in the cabinet | Open cabinet doors in very cold weather |
| Attics | Little heat, exposed runs | Insulate pipes, check for gaps in insulation |
| Supply line entry point | Cold foundation wall | Seal the opening, protect the line |
Walk your home with this list each autumn. Note any run you can reach and anything that seems cold to the touch.
Locate and Label the Main Water Shutoff
Your main shutoff is the single most useful valve in a freeze emergency. Find it before you need it.
In many homes it sits near where the water line enters, often close to the meter. Some homes also have a second valve on the other side of the meter.
Make the valve easy to use:
- Clear stored items away from it.
- Tag it with a bright label.
- Show everyone in the household where it is.
- Turn it gently once a year to check it moves.
- Note any valve that is stiff or leaks when turned.
Do not operate the utility’s curb valve or meter fittings. Those belong to the water utility. A stiff house valve is a job for a plumber.
Seal Drafts Without Blocking Safe Ventilation
Drafts freeze pipes faster than still cold air. Sealing small gaps near plumbing is one of the most effective steps.
Look for gaps around pipe penetrations, rim joists, sill plates, basement windows and dryer vents. Use caulk or foam rated for the location.
Do not seal combustion air openings, furnace or water heater vents, or required crawl-space ventilation without advice. Fuel-burning equipment needs air, and some vents are required for good reason.
Insulate Exposed Pipes Appropriately
Pipe insulation slows heat loss. It does not create heat, so it works best when some warmth reaches the area.
Good practice includes:
- Fitting foam sleeves snugly with no gaps at joints.
- Covering elbows and valves, not just straight runs.
- Taping seams so sleeves stay closed.
- Insulating both hot and cold lines in cold spaces.
- Keeping insulation away from heat sources and flues.
Electric heat cable can help on some runs. Use only products listed for the purpose, follow the instructions exactly, and have questionable installations checked.
Protect Hose Bibs and Outdoor Connections
Outdoor faucets are often the first fixtures to freeze. Water trapped in the line or in a connected hose has nowhere to go.
Before the first hard frost:
Disconnect and drain every garden hose.
Close the indoor shutoff valve for each outdoor faucet.
Open the outdoor faucet to let trapped water drain.
Leave it open if the fixture manufacturer recommends it.
Shut down and drain irrigation systems according to their instructions.
Frost-resistant faucets still need the hose removed. A hose left attached can trap water inside the valve body.
Keep Heat Available in Occupied Rooms
Heat is the best protection, and it needs to reach the pipes. A warm living room does little for a cold cabinet against an outside wall.
Keep the thermostat at a steady setting day and night during deep cold. Large overnight setbacks can let vulnerable runs drop too far.
If you use a space heater, follow the manufacturer’s instructions. Keep it clear of combustibles and never leave it running unattended.
Planning for Trips and Vacant Properties
Empty buildings are at higher risk. No one is there to notice a cold room, low pressure or a leak.
Before you leave in winter:
- Keep the heat on at a safe steady setting.
- Ask someone to check the property regularly.
- Give them your shutoff location and a contact number.
- Consider shutting off the main water supply.
- Ask a plumber about draining the system for long absences.
If you shut off the main water, check how that affects your heating. Some boilers and other systems need a water supply, so ask a qualified professional first.
Risks in Crawl Spaces and Exterior Walls
Crawl spaces and exterior walls hide pipes where you rarely look. Problems there can go unnoticed until water appears.
Check crawl spaces for gaps, missing insulation and damaged vent covers. Look for pipes resting directly against cold foundation walls.
For pipes inside exterior walls, the fixes are usually draft sealing and keeping the room side warm. Rerouting a line away from an outside wall is a larger project best discussed with a plumber.
When Opening Cabinet Doors May Help
Sink cabinets on outside walls trap cold air around pipes. Opening the doors lets room heat reach them.
This is a simple step for the coldest nights. Remove cleaning products or anything hazardous if children or pets can reach the open cabinet.
Opening doors helps only if the room itself is warm. It will not protect a cabinet in an unheated space.
Safe Options During a Cold Snap
When temperatures drop sharply, a few extra habits reduce risk for vulnerable fixtures.
- Let a vulnerable faucet drip slowly, which keeps water moving.
- Open sink cabinets on outside walls.
- Keep interior doors open so heat circulates.
- Keep garage doors closed.
- Check the coldest rooms morning and evening.
- Watch for faucets with sudden low flow.
A dripping faucet uses some water. Most owners use it only for the most exposed fixtures during the coldest nights.
What Never to Use to Thaw a Pipe
Some thawing methods create fire, injury or electrical hazards. Never use them, however quick they seem.
Do not use:
- Torches, lighters or any open flame.
- Heat guns or other high-heat tools.
- Charcoal, kerosene or propane heaters indoors.
- Electrical devices in or near standing water.
- Boiling water poured onto pipes.
Open flames near framing can ignite hidden materials inside walls. High heat can also damage pipes and fittings and make a burst more likely.
How to Recognize an Already Frozen Line
A frozen line usually shows itself at a fixture before it shows anywhere else. Watch for flow problems during cold weather.
Common signs include a faucet that delivers only a trickle or nothing, a toilet that will not refill, or frost on an exposed pipe. Sometimes one fixture fails while others work normally.
These signs suggest a blockage of ice, not a confirmed burst. Treat the line gently and assume it may already be damaged.
What to Do if Water Flow Stops
If a fixture stops flowing in deep cold, assume a frozen pipe until proven otherwise. Act calmly and safely.
Leave the affected faucet open so water can move as ice melts.
Check whether other fixtures still work.
Warm the room or cabinet with existing heat, never flame.
Look along accessible pipes for frost, bulges or splits.
Know where the main shutoff is in case water escapes.
Call a plumbing professional if flow does not return or the pipe is out of reach.
Do not leave a slowly thawing pipe unattended. A hidden split can start leaking as the ice melts.
What to Do if a Pipe Bursts
If a pipe bursts, stop the water first. Close the main shutoff, then deal with the damage.
If water is near outlets, cords or the electrical panel, stay out of the area and call for emergency help. Do not walk through standing water near live electrical equipment.
Once the water is off, open a faucet on the lowest level to drain lines. Move belongings, photograph damage and arrange repair. Our page on frozen and burst pipe repair covers what usually happens next.
Call (844) 442-1700 to be connected with an independent local provider for frozen or burst pipe help. Availability is confirmed when you call.
Comparison: Prevention, Thawing, and Repair
Prevention, thawing and repair are different stages with different risks. Knowing which stage you are in helps you act correctly.
| Stage | Goal | Who usually handles it | Main risk |
|---|---|---|---|
| Prevention | Keep water from freezing | Owner, sometimes a plumber | Missing an exposed run |
| Thawing | Restore flow safely | Owner with care, or a plumber | Unsafe heat or a hidden split |
| Repair | Fix a damaged pipe | Plumber | Water damage and access |
Frozen pipes, burst pipes and ordinary fixture blockages can look similar at first:
| Clue | Frozen pipe | Burst pipe | Blocked fixture |
|---|---|---|---|
| Flow at fixture | Little or none | May drop sharply | Low at that fixture only |
| Weather link | Deep cold | Often during thaw | None |
| Water escaping | No | Yes, often | No |
| Other fixtures | May still work | Pressure may fall everywhere | Work normally |
| Immediate step | Keep faucet open, warm safely | Shut off main water | Clean aerator or call a plumber |
Preparing a Household Shutoff Checklist
A short written checklist helps anyone in the house act fast. Post it near the main shutoff or inside a utility cabinet.
Include:
- Where the main shutoff is and how to turn it.
- Where the electrical panel is.
- Which outdoor faucets have indoor valves.
- A phone number for plumbing help.
- 911 for immediate danger to people.
- Unitil’s New Hampshire gas emergency line, 1-866-900-4115, for a gas odor after calling 911 from outside.
The gas line number comes from the Portsmouth Fire Department’s gas safety sheet. If you smell gas, leave first and call from a safe place.
Source: Portsmouth Fire Department — Gas Safety Fact Sheet, reviewed October 2026.
When to Ask a Plumbing Professional
Some situations go beyond safe home steps. Ask a professional when:
- A pipe is frozen in a wall, ceiling or crawl space you cannot reach.
- Flow does not return after the room has warmed.
- You see a bulge, crack or frost line on a pipe.
- Your main shutoff will not turn or leaks when turned.
- You plan to leave a property empty for a long period.
- Pipes have frozen in the same place before.
Repeated freezing points to a layout or insulation issue. A plumber can discuss rerouting, insulation or other changes. For how calls are handled, see how it works.
After a Freeze: Checking for New Leaks
A pipe that froze may have cracked without leaking right away. Check carefully once temperatures rise.
After a freeze, look for damp spots, drips, stains or low pressure. Check under sinks, around exposed pipes and below the area that froze.
A meter test can help reveal small leaks. If you find a problem, our water leak repair page explains how repair scope is typically decided.
Seasonal Habits to Repeat Each Autumn
Freeze prevention works best as an annual routine. Repeat these steps before the first hard frost.
- Drain and store garden hoses.
- Close and drain outdoor faucet lines.
- Check pipe insulation for gaps or damage.
- Seal new drafts around pipes and the rim joist.
- Test the main shutoff valve.
- Update your household shutoff checklist.
- Arrange a property checker for winter trips.
If you have properties in nearby towns, the service areas page explains how coverage is confirmed for each address.
Call (844) 442-1700 if your autumn check turns up a damaged pipe or a valve that will not close.
Frequently Asked Freeze-Prevention Questions
What temperature should I keep my home at to prevent frozen pipes?
There is no single safe number for every home. Keep heat steady day and night, and make sure warmth reaches pipes on outside walls and in cabinets.
Should I leave a faucet dripping during cold weather?
A slow drip can help on the most exposed fixtures during deep cold. It uses some water, so most people limit it to vulnerable lines.
How deep should a water line be to avoid freezing in Portsmouth?
We do not publish a single depth figure. Required depths and practices depend on code, the utility and the site, so ask the utility or a qualified plumber.
Can I use a hair dryer or heater to thaw a pipe?
Never use flames or high heat. Warm the room with existing heat and call a plumber if the frozen section is concealed, unreachable or near water and electricity.
Should I shut off my water before leaving for winter?
Shutting off the main can reduce damage if a pipe fails while you are away. Check first whether your heating system needs water supply.
Does pipe insulation stop pipes from freezing?
Insulation slows heat loss but does not add heat. It works best combined with draft sealing and some warmth in the space.
How do I know if a frozen pipe has burst?
Water escaping, falling pressure or new damp spots after thawing suggest a burst. Shut off the main water and arrange repair.