By Granite Trusted Pros · Last updated October 27, 2026
Why check your septic system before winter?
A problem is easier to fix while the ground is still soft and the tank cover is easy to reach. The NEHA winter guidance says a well maintained septic system is better able to handle the stresses of winter weather. It also warns that effluent from a failing system can freeze near the leach field and stop more effluent from soaking into the soil. That is one reason to look for trouble in the fall rather than in January.
What are the warning signs of a failing septic system?
EPA lists these common signs:
- water and sewage from toilets, drains and sinks backing up into the home
- bathtubs, showers and sinks draining very slowly
- gurgling sounds in the plumbing
- standing water or damp spots near or over the septic tank or leach field
- sewage odors around the tank or leach field
- bright green, spongy grass over the tank or leach field, even in dry weather
EPA also says soft, wet or spongy soil around the leach field when there has been no significant rain is a good sign of a system failure. An odor alone can have other causes, such as a roof vent, so EPA suggests having a local septic service provider or plumber look rather than guessing.
Is it a good time to pump the tank?
NHDES says septic tanks should be pumped every three to five years for optimal function, and to use an NHDES-licensed septage hauler. If you are due or are not sure when it was last done, fall is a convenient time to book. EPA adds that alternative systems with pumps, float switches or other mechanical parts should generally be inspected once a year. Our guide on how often to pump a septic tank in NH has more detail.
How do you help keep a septic system from freezing?
This advice comes from NEHA and the Minnesota Pollution Control Agency, a state with long, cold winters like ours:
- Fix leaky faucets, toilets and appliances. NEHA says small trickles of water can freeze inside a pipe and eventually freeze it solid.
- Check for open, broken or uncapped risers, inspection pipes and manhole covers that let cold air in, and have a septic pro repair them.
- Let the grass over the tank and leach field grow a little longer in late summer and fall for extra insulation.
- Keep cars, trucks and heavy foot traffic off the system. Compacted snow and soil insulate less, and the MPCA says to pay special attention to the area between the house and the tank.
- Do not plow, shovel or pack down the snow over the system. Loose snow is insulation.
- For a new system or one that has frozen before, ask a pro about extra insulation. Both sources mention a loose layer of mulch, hay or straw 8 to 12 inches thick over the pipes, tank and leach field. The MPCA says not to add mulch to a system that is already frozen, because it slows thawing in spring.
What if you are away for part of the winter?
NEHA says that if you will be gone for more than a week, leave the heat on and consider having someone run warm water regularly. If you will be gone for several months, talk to a septic pro about pumping the tank before you leave. NEHA notes that in certain areas pumping a tank can cause it to pop out of the ground, so this is a question for a pro, not a do it yourself job.
What are the signs your septic system is freezing?
Slow or stopped drains in cold weather can point to a frozen line. If you have a pump, NEHA says that hearing water constantly running into the pump tank, or the pump turning on and off, can mean the system is frozen. In that case, shut off the pump and call a septic system service professional. If you think the system is starting to freeze, NEHA suggests using warm water and spreading laundry and dishwasher loads out to at least one warm load a day.
What should you never do to a frozen septic system?
NEHA and the MPCA agree on this list:
- do not add antifreeze, salt or a septic system additive
- do not start a fire over the system to thaw it
- do not pump sewage onto the ground
- do not leave water running all the time, since that can overload the system
EPA does not recommend septic additives at any time of year. A pro has tools such as cameras, steamers and jetters to find and clear a frozen line, according to the MPCA, and NEHA notes that unless the cause is fixed, the system will probably freeze again next winter.
What should you do in spring?
NEHA recommends a septic inspection after winter ends, whether or not the system froze, because snowmelt can saturate the ground. If your system froze, ask about insulated pipes or insulated covers so it does not happen again.
Where can I find a septic company near me?
Our septic service directory lists local septic pumping and service companies in Milford, Nashua, Bedford, Merrimack, Amherst, Manchester, Concord, Windham, Hollis, Bow, Salem and nearby towns, with phone numbers you can call directly. Ask any company you call to confirm it is an NHDES-licensed septage hauler. Selling this winter? See what NH law requires when you sell a home with a septic system.
Frequently asked questions
What are the warning signs of a failing septic system?
EPA lists sewage backing up into the home, slow drains in tubs, showers and sinks, gurgling sounds in the plumbing, standing water or damp spots near the tank or leach field, sewage odors, and bright green, spongy grass over the tank or leach field even in dry weather.
Can a septic system freeze in New Hampshire?
Yes, septic pipes, tanks and leach fields can freeze in cold weather. Cold-climate guidance from NEHA and the Minnesota Pollution Control Agency points to leaky fixtures, compacted snow or soil, open risers, and low water use while a home is empty as common causes.
What should I do if my septic system freezes?
Call a septic system service professional. NEHA and the Minnesota Pollution Control Agency both say not to add antifreeze, salt or septic additives, not to start a fire over the system, not to pump sewage onto the ground, and not to leave water running, which can overload the system.
Should I pump my septic tank before winter?
NHDES says tanks should be pumped every three to five years, so if you are due, fall is a convenient time. NEHA adds that if you will be away for several months, ask a septic pro about pumping before you leave, and notes that in some areas pumping a tank can cause it to pop out of the ground.
Do septic additives help in winter?
EPA does not recommend septic additives, saying they can be ineffective or even harm system operation. NEHA and the Minnesota Pollution Control Agency also say not to add them to a frozen system.
Sources
- EPA: Frequent Questions on Septic Systems
- EPA: How to Care for Your Septic System
- National Environmental Health Association (NEHA): Guidance for Septic Systems Before, During, and After Winter Weather
- Minnesota Pollution Control Agency: Don't let your septic system freeze
- NHDES: Get Pumped! New Hampshire
This guide is general information, not professional advice. Talk to a licensed septic pro about your own system.