Installing a septic tank is an excellent solution for managing waste, especially if you live in a remote area or prefer to bypass local utility services.
Septic tanks, however, come in a wide variety of sizes, forms, and types. Selecting the appropriate tank for your home is vital. Septic tanks are sized based on their working capacity, which is the capacity of the 1st chamber (in a two-chambered tank) OR the capacity of the 1st tank in a two-tank system.
Size of Septic Tank based on Bedroom Count
Below is a basic table that shows approx minimum working capacity regarding septic tank sizing in Alberta. Keep in mind that these minimum capacities are only valid for homes that have basic fixtures. If your home has additional fixtures, large tubs, a large number of bathrooms, etc, these minimum capacities are not valid for proper tank sizing.
Number of Bedrooms | Minimum Working Capacity Volume |
1, 2, or 3 bedrooms | 3,360 L (740 Imp gals) |
4 bedrooms | 4,260 L (940 Imp gals) |
5 bedrooms | 5,220 L (1,150 Imp gals) |
6 bedrooms | 6,130 L (1,350 Imp gals) |
A typical Canadian home’s occupants are expected to use 50 imperial gallons of water each day.
Size Factors for Septic Tanks
There are various classifications for septic tank sizes. There are the tank’s actual dimensions, the septic tank’s minimum capacity expressed in imp gallons, and the specifications for the distribution box, baffles, and drainfield’s size and form.
Dimensions of the Tank
The dimensions of a tank totally depends on what capacity is needed. Most concrete septic tanks (most popular in Alberta) are around 4-5ft tall, 6-8ft wide, and 10-13ft long (for most 4-6 bedroom homes).
Working Capacity
As mentioned above, the working capacity of the septic tank (in Alberta) is calculated to allow for min 24hrs of retention time in the working chamber. The formula for this calculation is Estimated Peak Flow + Sludge & Scum Accumulation over 3 years.
Materials for Tanks
Owing to construction issues, septic tanks can be made from a wide range of materials, all of which affect the maximum size.
- Concrete: The most frequent material used to construct septic tanks is concrete. The size range is enormous here since concrete is pourable. Many concrete septic tanks are “integral” tanks, which means it has two chambers (working chamber + dose chamber). Concrete tanks have the deepest burial rating (up to 5m or 15ft).
- Fiberglass and plastic: These tanks usually only have a burial rating of 4-6ft, so they can only be used in limited installations. They can be more chemical resistant to components in the sewage and surrounding soils as compared to concrete, however they can crack easier than concrete during freeze-thaw cycles. They are lighter weight than concrete and can usually be placed with a small excavator.
- Steel: Steel is very uncommon for residential applications; it is much more expensive than the other options.
Advice for Selecting the Correct Septic Tank
To make sure your size requirements are satisfied when purchasing a new septic tank, it is best to have a professional designer/installer assess your home, count the bedrooms, bathrooms, and fixture units to calculate the minimum capacity that the local authority will require.
Avoid Overspending
Grossly oversizing a septic tank does not help. The only time to oversize your septic tank would be if you know that you might be renovating or adding bedrooms /bathrooms in the near future.
Regular pumping/cleaning
Regular pumping is necessary to guarantee effective functioning and a respectable lifespan for septic tanks. Tanks installed after 2009 (in Alberta) are supposed to be sized for an expected 3yr interval between pumping/cleanings. Septic tank pumping typically costs around $400 – $500.
For expert advice and assistance with your septic system needs, contact Soilworx today!
