Winterizing Septic Systems, Pro Tips – Solutions, Prevention


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Winterizing Septic Systems, Pro Tips

Your septic system is frozen, now what? Let’s go over some of the symptoms, solutions and preventative measures on keeping your septic system safe in winter.

In colder climates, wastewater professionals and homeowners may have to contend with several additional challenges over and above the normal septic system installation challenges or system failure issues that may arise from time to time.

While wastewater professionals usually see the number of system installations slowing down over winter due to the limitation of installing a system in frozen ground, the volume of emergency work typically rises dramatically, due to system failures caused by frozen septic lines for example.

septic system services

Like all emergencies, these tend to always occur during the holidays and as luck would have it when the weather is at its worst.

The Boy Scouts motto ‘Be Prepared’ is a mantra that should be heeded by all, but particularly by owners of septic systems — especially ahead of winter, when extremely cold conditions can cause a septic system to freeze up. This article will help you better understand some of the potential problems you may be presented with when the mercury drops and offers some tips and solutions on how to prepare a septic system for the winter in order to avoid these potential pitfalls.

How Cold Temperatures Affect an Onsite Septic System

 Temperature can influence the rate of flow and mixing within the septic tank, as well as the nitrification process, which together with pathogen removal, will be slower in colder climates. Consequently, sewage can take longer to break down and bacteria and viruses are likely to survive for long periods in cold soils, due to the microbial activity being inhibited when temperatures drop.

Wastewater treatment is essentially a biological process that depends on living microbes to get the job done effectively. The microbes that break sewage down are fair weather critters that are more active in warmer temperatures.

Consequently, microbial activity declines as temperatures drop, and when temperatures drop to as low as 35-39 degrees F, the microbes go into a dormant state. What this means, is that sewage is processed slower at lower temperatures, and can stop altogether if temperatures drop as low as 35-39 degrees F.

However, because septic tanks are buried below ground, in colder climates the sewage effluent typically tends to be around 10-20 F degrees warmer than ambient soil temperatures, which, together with the heat from the surrounding soil, keeps temperatures in the soil treatment area higher than 35 degrees F.

frozen septic tank lid

In colder climates, the onset of freezing may arise when the temperature of the wastewater flowing into the septic tank is very low, particularly in shallow septic system installations, or systems that consist of a large volume septic tank or multiple tanks/components connected in a series that may be partially or completely surrounded by frozen soil.

In cases such as these, it may be necessary to insulate the septic system in order to ensure internal temperatures are maintained at a level that is conducive for microbial activity — and by extension digestion — to take place effectively.

insulated septic tank

Frozen Septic System Symptoms

If you have a septic system, experiencing frozen lines or having a septic tank that is now rock solid with ice, is certainly not one of those situations that you plan for.

There are possible answers as to why freezing has occurred in your system, this can stem from a shallow piping network to uninsulated septic tanks…but let’s not forget how Mother Nature can factor in.

Snow acts as a fantastic insulator, in fact up to an R1 rating per every 1 inch of snow cover so whenever the temperatures drop prior to snowfall, then we can often see problems arise in the sewage system.  It is important not to compact the snow around the septic system components, this will keep the insulating factors of snow working in your system’s favour.

Let’s touch on some of the reasons why freezing occurs in a couple of different system types: 

In a conventional septic system, freezing can occur if there is slow running water from fixtures, water softeners or the emptying of furnace condensation into the sewage system. 

This slow running water can quickly cause ice to accumulate in the drain lines, eventually causing complete blockage from slow ice formation.

With regular household use, frequent warm water, soaps, waste and detergents rise the level of the wastewater’s freezing point and the constant biological activity in the septic tank can certainly keep the entire system from freezing. 

Now if there is a slow trickle of water going in through the system, and let’s say no one is in the home for a week or two…this is usually when Murphy’s Law comes in for a visit.  There are freezing conditions with limited snow cover, the drain lines start to accumulate with ice, eventually blocking the system and causing back up through the lines into the home.

preventing septic freezing

With extremely low temperatures even the constant movement of wastewater through the septic system isn’t going to keep the system from freezing.  In cold regions, preventative measures are the key, and properly designing a septic system is going to factor in the extreme temperatures.

In a pressure distribution septic system, there is going to be fast-moving fluids moving through the network lines.  Often the drain field can be a relatively far distance from the septic and pump tanks, what this means is the effluent is cooling down as it travels through the piping network. 

With every 90 degrees turn or level piping, there is going to be some ice formation if the design didn’t take into account the possibility of extreme conditions.  In the dispersal piping network in the drain field, the orifices where effluent gets dispersed into the soil can easily start to form ice and eventually clog.  

septic freezing

This can lead to clogging the entire drain field, eventually blocking any effluent from being dispersed.  This will cause the system to malfunction, the high water alarm in the tank will go off, and if the homeowner is not careful with water usage, the sewage system will eventually back up into the home.

How to Winterize an Onsite Septic System

As the cold weather approaches, homeowners are advised to check that their septic system is operating efficiently and that all routine maintenance is up to date, to ensure that things will continue to run smoothly over the winter months.


Because colder temperatures can adversely affect the efficiency of the septic system, we recommend that you take steps to insulate your system to ensure maximum efficiency over winter.

Insulating the septic system lines during installation

If you live in a cold climate and your septic pipes are exposed to the elements, there are a few ways to improve insulation:

Firstly, you can simply use insulated sewage piping that comes encased in an insulating urethane foam sandwiched between a polyethene exterior sleeves. Installation is simple and it is not likely to come apart.

freezing septic lines

Alternatively, you can wrap the sides and top of the pipes with insulation foam sheets specifically rated for use buried under soils. Insulation foam designed for indoor use is likely to absorb moisture from the soil, rendering it ineffective for use underground.

It is also likely to move about rather than stay wrapped around the pipes once trenches are back-filled with soil and gravel. So if you decide to go this route, make sure you purchase insulation sheets that are suitable for use in soil.

Finally, you can enclose the pipe within a larger pipe that serves as a sleeve, effectively creating an air space around the sewage pipe that provides some form of insulation.

While this may be suitable for areas that don’t suffer extended episodes of freezing, it may not be adequate for areas that are subjected to longer bouts of freezing temperatures.

Heat tape can be used provided the temperature of the tape is rated for PVC or Polyethylene piping. This can sometimes be challenging though as there has to be an electrical receptacle near the line or lines being taped.

septic freezing

Frozen Drain Fields, Insulation and Prevention

In order to protect the drain field and prevent it from freezing, homeowners should stop mowing the grass that lies above the drain field from around mid-September.

By allowing the grass to grow, it will help retain snow, providing an insulating layer over the soil treatment area that can help reduce the likelihood of freezing.

Another option, particularly for homeowners who don’t have lawns, is to spread an insulating layer of leaves or straw over the area to retain heat and prevent the system from freezing.

septic insulation

Soil that lacks vegetative cover is likely to cool down more rapidly, allowing frost to penetrate to greater depths within the soil. This is particularly important for seasonal homes that are closed up for most of the winter.

Soil Compaction, this is of key importance, when regular vehicle or foot traffic goes over components of the septic system can greatly increase the chances of the frost line to form deeper into the soils.  Keep this in mind and avoid any kind of traffic over your septic system, this is a vital precaution not only on freezing factors but also to keep pipes or system components from breaking or shifting.

How to Prepare a Seasonal Septic Tank from Freezing

Many residents who inhabit homes in the colder parts of the country only reside there over the summer, opting to move to areas where temperatures are warmer and more bearable during the harsh winter months. In order to prolong the lifespan of septic systems serving these seasonal homes, and to ensure they continue to operate efficiently, it is vitally important that they are shut down over the winter.

Implementing the following steps in the fall can help reduce the likelihood of a seasonal septic system freezing up and presenting a problem when the owner returns in spring.

Preparing Sewer Lines from Freezing, Seasonal Cabin & RV

 If the home is going to be closed up over winter it is best to shut off the water supply to the house and drain the water lines completely. To do this, drain the water pump then let it run for a few seconds to remove any water remaining in the lines.

Open all the taps and leave them open. Drain the septic system’s pressure tank completely. Flush all the toilets in the house.  Remove all drainage hoses for the washing machine and/or dishwasher, and check that any flexible hoses in sinks, wash basins or bathtubs have been completely drained.

Clear the water from the tub by running it for a couple of seconds before draining the tub. Disconnect all electrical plugs supplying power to your water appliances. When the owners return in the spring, simply reconnect everything, ensuring that the lines are flushed before use.

If you decide to leave the water connected over the winter months, make sure there are no drips or leaks, as a constant slow flow of water can cause the septic system to freeze up — a common problem when high-efficiency furnaces are left on over the winter.

Is RV Anti-Freeze Safe for Septic Systems

The common type of antifreeze used in automobile cooling systems is Ethylene Glycol. This is not safe to use in any part of a home water system. … Propylene Glycol is not harmful if swallowed in small amounts but it is still not recommended for use in water supply systems. 

antifreeze in septic systems

Now there may be some great advancements in certain Glycols being septic safe, but I would be very wary of using these products.  What one has to remember is that it is vital to keep the active biology in the tank and in the drain field active, not clogged with chemical substrates.  Bacteria in the tank and in the drain field are actively working, it is essential not to interrupt this biology with unknown factors that can kill the ecology.

Furnace Preparation

When leaving the furnace on over winter, we recommend draining the water pipes to prevent freezing. If left on, make sure there are no slow drips that can cause the system to freeze up, as slow leaks tend to freeze more readily than a faster flow of water. If you spot a leak, divert the excess water to a bucket or floor drain to prevent it from slowly flowing into the septic system, potentially causing it to freeze up.

If you opt to turn the furnace off, ensure that the hot water pipes and a steam system is free of any water unless antifreeze has been added to the system. When leaving a furnace on over winter it is a good idea to install a thermostat that is able to maintain the indoor temperature between 40-50 degrees and to wrap heat tape around pipes to insulate them.

Septic Tank Maintenance

 If the home is going to be closed up over the winter months, you may want to consider having your septic tank pumped out beforehand. Leaving the tank full of sewage over winter when the system is not used can cause the sewage inside to become cold and maybe even freeze.

why do I need to pump my septic tank

When the residence is opened again in spring the ground may not have thawed sufficiently to warm up the cold sewage entering the drain field, which may, in turn, lead to less efficient processing of the effluent.

However, having said that, you may need to tread carefully here if the site has a high water table and your tank has not been specifically designed for these conditions. An empty tank may ‘float’ upwards as the level of the water table rises, particularly in areas that are prone to heavy winter rainfall.

Additionally, it is important to implement measures to ensure the septic system is well insulated to prevent it from freezing. Alternately a tank heater can be installed as a short-term solution, or you can speak very nicely to your neighbours, friends or family living nearby and ask if they can pop in once a week or so and run the washing machine to ensure there is a regular flow moving through the system.

septic tank heater

If the holding tank needs to be pumped out, make sure to do this before winter sets in, as a thick covering of snow could make accessing the tank more difficult.

Also check that any pump housed within the system itself is working properly, as this could fail if temperatures plummet. Check the riser lids for damage, and repair or replace any that look suspect.

Now is a good time to inspect the drain field for any surface ponding. Should there be any evidence of ponding, ensure that this is attended to before rain and/or snow add to the problem.

Septic Freezing Problems & Preventative Measures

 Septic lines are usually installed within the upper layers of soil so as to allow sufficient depth of soil to facilitate efficient treatment by bacterial communities living in the soil matrix as the effluent filters through.

Consequently, these pipes are not normally installed below the frost line, and therefore any water remaining in the pipes can freeze, causing a blockage in the pipeline.

Once blocked, the only immediate viable solution is to have the pipes jetted, which besides the additional expense, can be tricky considering your yard is likely to be frozen over or covered in snow and conditions are not likely to be very hospitable for the contractors responsible for doing the jetting.

There are several things that can cause the pipes within a septic system to freeze, including:

  • A bow in the pipeline or low point that allows water to collect rather than drain freely from the pipe;
  • Exposed or shallow lines that are exposed to frost;
  • A slow leak or dripping condensate from a high-efficiency furnace that causes water to slowly trickle into the pipes, but because this is in insufficient volumes to create an adequate flow, it can freeze up in the pipeline causing a blockage.

Therefore, in order to prevent water from collecting and accumulating in the septic lines and potentially becoming frozen, the pipes within- and feeding the drain field need to be correctly sloped to ensure adequate drainage and properly bedded to prevent the buried pipes from becoming bowed.

Using straw or leaves is going to add an extra insulated barrier from freezing temperatures, spread enough over the septic system components, drain lines and even drain field to provide enough insulation against possible freezing. 

How to Thaw a Frozen Sewer Line

Although any type of work on your septic system should involve a professional, sometimes emergency situations can occur at inconvenient hours or in areas where a pro isn’t readily available.

Let’s go over some emergency steps that can be conducted:

  • Locate the septic tank and remove the lid.  Condensation from the septic tank can cause the lid to freeze to the tank.  Use hot water to help the lid release.  Do not use a torch as this can ignite methane gases in the septic tank.
  • Adapt a PEX hose to your garden hose or hot water pressure machine and insert it through the inlet of the septic tank, towards the home.  This will keep the water flow moving into the septic tank and not backing up into the home.  You can use a garden hose but PEX is less flexible and can go deeper in the pipeline.
  • A high-pressure nozzle can be used with the warm water to start breaking apart the ice in the pipe, eventually, the ice will melt and release.  Some pros use steam or hot water to speed up the process but the high temperature may cause the PVC to crack.
  • Once you feel the ice being broken up in the line, slowly run warm water from the home to ensure it flows into the septic tank and breaks up any further ice formations. 
thawing septic system

Thermal blankets can thaw out the ground if digging around septic system components are necessary.  These ground thawing blankets can be plugged in and left until the necessary depth is thawed in the soil.

thawing a frozen drain field


 As we can see, a little pre-winter preparation and foresight can go a long way to ensuring your septic system continues to work efficiently over the cold winter months.

Simple measures, such as ensuring your septic system is well insulated; that there are no slow leaks or drips that can cause water to accumulate and freeze up within the pipes; and that septic lines are correctly sloped and bedded; can mean the difference between you relaxing by a crackling fire enjoying a hot cup of hot chocolate when things freeze over, or frantically plying a freezing jetting contractor with hot chocolate in an effort to thaw him out.

Luis Goncalves, ROWP, IN, PL

I fell into this amazing trade quite by accident, I have always loved being around heavy machinery and moving earth and in contrast love working with designing things.  This trade in the septic field has led me down a wonderful path of exploring all of my skills and passions while working hard at achieving success.

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