Power Outages, Generators, and Basement Floods

Storms in New Hampshire reliably produce three categories of damage we get called for every year: electrical surges that destroy HVAC controls and electronics, generator problems from systems that were not exercised or not properly installed, and basement flooding that submerges furnaces, boilers, and water heaters. Most of the damage is preventable with basic preparation.

At A.J. LeBlanc Heating, our electricians, plumbers, and HVAC technicians have helped southern NH families through more than a few of these. Here is what we tell customers ahead of every storm season.

How power surges damage your home

A standard NH residence is served with 240 volts of electricity (two 120-volt legs plus neutral and ground). Household electronics tolerate roughly plus or minus 10 percent, so normal voltage swings between about 110 and 130 volts are fine.

The problem is what happens during a storm or grid event. A lightning strike on or near a utility line, a tree taking down a transformer, or a switching event during a restoration can briefly push voltage to 150 volts or higher. At those levels, electronic controls explode, burn out, or short circuit.

Vulnerable equipment in a typical NH home:

Furnace and boiler control boards
Gas and oil burner controls and transformers
Heat pump and AC compressor controls
Smart thermostats
Garage door openers
Security and fire alarm panels
Variable speed pool pumps and well pumps
TVs, computers, and home networking equipment

What to do when you do not have a generator

If a major storm is forecast and you do not have backup power:

Unplug high-value electronics before the power goes out: computers, TVs, audio equipment, anything with a charger.
Switch off the breakers at your panel for the HVAC system and well pump. When power is restored, an inrush surge will not reach the protected equipment.
After power has been stable for at least 15 minutes, switch the breakers back on one at a time with a few seconds between each.
Plug high-value items back in only after voltage looks normal (lights are steady, fridge running properly).

Whole-house surge protection

A whole-house surge protective device (SPD) installs at the main electrical panel and protects everything downstream. Unlike a power strip with surge protection, an SPD intercepts surges before they reach individual circuits and is designed to handle far larger transient voltages.

Installation is straightforward for a licensed electrician.
Cost is small relative to the value of the equipment protected.
Many homeowners pair an SPD with point-of-use protection on the most sensitive equipment (computer, server, smart panel).
An SPD is not a consumable on a calendar schedule. Check the status indicator periodically (e.g., seasonally); replace the device when the indicator shows protection is exhausted, after a major surge event such as a nearby lightning strike, or once it passes its rated service life (typically 10 years for residential SPDs). Our whole-house surge protection guide covers SPD selection and replacement in detail.

Generators: standby vs. portable

Portable generators

Portable generators run on gasoline, propane, or natural gas and connect through extension cords or, ideally, a manual transfer switch installed at the panel.

Run the generator outside, at least 20 feet from any window, door, or vent. Carbon monoxide from a generator can kill within minutes in an enclosed or partially enclosed space.
Exercise the generator a few times a year. Run it under load for at least 15 minutes. A generator that sits unused for two years usually will not start in an emergency.
Let the engine warm up and stabilize before energizing loads.
If powering loads through a manual transfer switch, turn circuits on one at a time with a few seconds between each.
Never back-feed a generator through a dryer or other outlet. It is dangerous to line workers and illegal in NH.

Whole-house standby generators

A standby generator is a permanently installed unit (typically Generac, Kohler, or Cummins) that runs on natural gas or propane and starts automatically within seconds of a power outage. A licensed electrician installs an automatic transfer switch at the panel.

The system exercises itself weekly for several minutes on a programmed schedule.
Annual professional service is required for warranty coverage and reliability.
Sized from a load calculation by the installer, not guesswork. Typical NH whole-house standby units run 11 to 26 kW, and a power management module lets a smaller unit cover more of the house. See our generator sizing guide for how that works.
Modern units include cellular monitoring so the homeowner is notified of run cycles and any fault codes.

Cold-weather plumbing protection

If the power is out long enough that the house cools and pipes are at risk:

Open faucets to a slow trickle on exterior-wall plumbing runs to keep water moving.
Open cabinet doors under sinks on exterior walls to circulate warmer interior air.
If the home will be unoccupied during extended cold without heat, drain the pipes, fill traps with antifreeze, and shut off the main water supply.
If you have a generator running essential circuits, prioritize the heating system and the well pump if you are on a well.

Recovering from a flooded basement

Furnaces, boilers, and water heaters that were submerged or partially submerged must not be restarted until a licensed technician has evaluated them. Industry safety guidance from AHRI is strict on this point:

Gas valves, safety controls, and burner components that contacted floodwater must be replaced, not dried and reused. Corrosion begins inside these components as soon as they are submerged, and the damage is invisible even when a part looks clean and dry on the outside.
This applies whether or not electrical power was on during the flood. Submersion is what compromises valves and controls, not electricity.
Equipment that was partially or fully submerged frequently warrants full replacement rather than repair. A licensed technician must make that call before any restart.
Insulation jackets that absorbed contaminated water should be removed and replaced.

Need help preparing or recovering?

For surge protection, generator installation or service, post-flood HVAC recovery, or 24/7 emergency service in southern NH, contact A.J. LeBlanc Heating. Serving New Hampshire families since 1928.

Frequently Asked Questions

How often should I exercise a portable generator?

At least once every three months, under load, for 15 minutes or more. Use fresh fuel and a stabilizer if it sits between runs.

Will a whole-house generator power my air conditioning?

Properly sized, yes. Sizing starts with a load calculation by the installer; typical NH whole-house standby units run 11 to 26 kW, and a power management module lets a smaller generator carry the heating system, well pump, refrigerator, and central AC by shedding lower-priority loads. Smaller essential-circuits systems are a valid lower-cost option for homes that do not need full coverage.

Is a surge protector enough, or do I need a whole-house SPD?

Plug-in surge strips protect against minor surges on the circuit they are plugged into. A whole-house SPD installs at the panel and protects everything downstream, including hardwired equipment like the furnace and water heater. Both layers together provide the most protection.

What should I do immediately after a basement flood?

Shut off power to any submerged or wet equipment before entering the water. Do not attempt to restart anything that was wet. Call a licensed technician to inspect the heating system, water heater, and electrical components.

Do you offer 24/7 emergency service?

Yes. Call 603-623-0412 any time for no-heat, no-hot-water, or storm-related HVAC emergencies in southern New Hampshire.