Originally, septic tanks had one chamber but for the most part, the one-chamber design has almost completely been replaced by the two-chamber design.
As a result of the efficiency achieved in the two-chamber design, the three-chamber tank was also introduced.
As the name suggests, the three-chamber system has three chambers that are used as pre-treatment chambers of the waste before the wastewater is sent to the drain field area for the final treatment process.
Whether a tank is one chamber, two chambers, or three chambers, the mode of operation is the same—the solid waste will settle at the bottom to form the sludge layer while the grease will float on top to form the sludge layer.
As the solid waste gets liquefied, it moves to the next chamber and the process repeats until the waste finally gets to the leach field.
But since one-chamber ones are almost obsolete, we will only look at the two and three-chamber ones.
Pros and Cons of Three-Chamber Septic Systems (Over A Two-Chamber System)
Two-chamber septic tank systems are the most commonly used in most homes today.
In fact, it is very unlikely to have a one-chamber system unless you live in an old house with a septic system that was installed before the 1990s.
In a two-chamber system, the first chamber acts as the pretreatment stage where scum and sludge settle.
The partially treated waste is sent to the second chamber where it is treated further before it is sent to the drain field area.
A two-chamber system is small, cost-effective, and ideal for rural areas.
The main drawback is it has limited room and will therefore fill up faster than a three-chamber system would.
The three chambers in a three-chamber system give more room and time for the treatment of solid waste.
Just like in the two-chamber system, the first chamber in the three-chamber design is the pre-filtration stage where the sludge and scum mainly settle.
The other two chambers offer a finer filtration and the result is better-treated water that gets released into the drain field.
Another notable difference between three-chamber and two-chamber systems is that three-chamber systems can handle large volumes. This means they do not fill up as quickly and will therefore not require pumping s regularly.
Three chamber systems also break down scum more efficiently while most of the scum in the two chamber systems will only be removed through pumping.
The way the chambers are designed, waste will only move to the next chamber if it fills up in the first one.
This means the waste will take longer in the tank before it is sent out to the drain field. As a consequence, the effluent will be better treated in the three-chamber system.
The main drawback of three-chamber systems is that they have more components which not only means they are more costly to install but also harder to maintain.
These coupled with the initial costs of purchase and installation make them less desirable for homeowners.
However, they are less likely to pollute the groundwater because of the more thorough breakdown of solid waste.
The Cost Of Installing A Three-Chamber Septic Tank
Three-chamber septic tanks are more sophisticated and therefore cost more than two-chamber ones.
However, the installation process is pretty much the same.
So, the only significant difference in the cost is the purchase price but the figure your contractor will quote for the installation should not be any different from what it would cost to install a two-chamber system of the same size.
The table below gives a rough estimate of the installation costs for septic tanks
| Number of Bedrooms | Cost |
| 1 | $500-$900 |
| 2 | $700 -$900 |
| 3-4 | $900 – $1500 |
| 5-6 | $1200-$1600 |
| 6-7 | $1500-2500 |
These are just ballpark figures as the exact cost will vary depending on your location.
Additionally, the cost of the tank installation may also be determined by the material used.
For instance, Forbes estimates that a basic concrete tank will cost $750-$1700 whereas a fiberglass tank of the same volume will cost $1450 – $2000.
So, the only way to be sure of the exact cost is to request a quote from a contractor.
How Big Should A Three-Chamber Septic Tank Be?
Even though three-chamber septic tanks are more efficient than two-chamber ones, they are still subject to government regulation which requires the size to be determined by the number of bedrooms.
| Number of Bedrooms | Tank Capacity |
| 1 – 2 | 750 |
| 3 | 1,000 |
| 4 | 1,250 |
| 5 | 1,250 |
As you may imagine, the performance of the tank will largely be impacted by its size.
The larger the size, the more volume it can handle and the more efficiently it can handle waste.
However, big is not always better and there are some cases where a small tank may be more efficient than a larger one.
For instance, if you install a tank meant to serve 5 people on a property that is occupied by one, the large tank may struggle to get enough bacteria to break down the waste.
The same case applies to houses that are not occupied all year (e.g. log cabins and other vacation properties).
In an ideal scenario, bacteria are sent into the septic tank with every flush of the toilet and these bacteria revitalize the bacteria population in the tank.
When the bathroom is not actively used, the system may not sustain itself and that can result in all kinds of issues.
Also, if you renovate an old house and add a bathroom/bedroom, you may be required by law to install a larger septic tank.
It is therefore advisable to consult with the local authorities to be sure you are not in violation of any bylaw before you commence any construction work.
Maintenance
A three-chamber septic tank requires regular maintenance to prevent problems such as backups, odors, and groundwater contamination.
Here are some essential maintenance tasks that are recommended for these types of tanks:
- Pumping: Be sure to pump your tank every 3-5 years or as often as your local regulations require. Pumping removes the scum and sludge thereby giving the tank more space for new wastewater from the home.
- Water usage: The whole idea of having three chambers is to allow the solid to settle in the tank for longer to allow bacteria enough time to liquefy it. However, this process may be hampered by excessive water thereby causing system failure. Avoid using too much water and fix any faucet leaks to help prevent hydraulic overload.
- Proper Waste Disposal: Flushing non-biodegradable items such as feminine hygiene products, baby wipes, and pharmaceuticals can cause blockages in the septic system. Proper waste disposal can help prevent these issues.
- Inspections: Prevention is always better than cure. As such, you may want to perform regular inspections to help you nip any issues in the bud. A professional septic service can perform an inspection and recommend any necessary repairs.
Ideal Soil Types for Three Chamber Systems
A three-chamber system is a conventional system and as such, it is only ideal for soils that have good permeability and absorption.
The soil should not be clay because that would interfere with the percolation and it should not be sandy because the wastewater would sip through too fast before it is sufficiently treated.
Additionally, there should be enough depth between the soil and the water table to avoid water pollution.
Any soil conditions that do not meet these basic requirements will call for the installation of an advanced system.
You may want to check: What Is The Best Septic System For Clay Soil?
Three-Chamber Septic System Lifespan
In terms of durability, three-chamber systems will just last as long as the two-chamber ones –i.e they should last for 15 to 40 years.
The longevity of the septic tank has less to do with how many chambers it has and more to do with how it is maintained.
If you stick to the recommended pumping schedule and practice other maintenance practices, the tank should last for at least three decades without any issues.
Closing Thoughts
The two-chamber septic tanks may have been the de facto standards for most modern houses that have conventional systems but the onset of three-chamber systems is bound to change the trend.
Even though they are costlier to buy and maintain, they are more efficient and less likely to pollute groundwater.
So, do not shy away from installing a three-chamber system on your property because you can rest easy knowing you have a system that will work almost flawlessly for years on end.