Sizes of Septic Tanks & Shapes

Septic tanks are typically made of fiberglass, plastic or reinforced concrete. Metal tanks are also available, but these can corrode rapidly and are not typically recommended. Septic tanks may be constructed in rectangular, round or oval forms, but the shape of a septic tank does not typically affect its function. The main factor in picking a septic tank is making sure you have the right size to adapt your house.

Concrete Tank Construction

Concrete septic tanks are heavy and usually rectangular in shape. They are typically constructed in one of 3 different types: mid-seal, top-seal, or monolithic. Mid-seal tanks contain 2 halves, and these are joined with a mastic sealant. A top-seal tank is just a one-piece cylinder using a concrete lid. Monolithic cast tanks are cast in a factory as one unit, which makes them more waterproof but also more costly than other forms of concrete tanks.

Debate and Plastic Tanks

Fiberglass and plastic tanks are produced in around or capsule-like shapes and have a nearly impervious waterproof seal. They’re more costly than concrete units, but since these tanks are formed as one piece, there are no seams, the tanks are lightweight, and they are more resistant than concrete tanks to impact cracks.

A Range of Tank Sizes

Septic tank sizes are measured in liters, based on the quantity of sewage the tank can hold. Septic tanks must hold at least 2 days’ worth of sewage from your house so the seams correctly separate from the liquids prior to the liquids move in the absorption field. The tank size is based on the amount of bedrooms in your home. Standard tank sizes are usually 1,000, 1,250 and 1,500 gallons, and these suit most homes. Typically, the minimum tank liquid capacity of a single- to three-bedroom house is 1,000 gallons. A four-bedroom home requires a minimal 1,250-gallon tank, and a house with five bedrooms requires a minimal tank fluid capacity of 1,500 gallons. In case you have a spa or whirlpool, add one-bedroom worth of capacity per fixture.

Estimating Your Needed Tank Size

Tank dimension is calculated using a very simple calculation, although other factors, such as soil type, needs to be considered as well. For this reason it is best to get a specialist assess the site and your house to determine the ideal size of tank for your requirements. However, to obtain an idea of the minimal size required for your house, multiply 150 gallons per bedroom, and multiply the total by 2 to allow for your 48-hour retention time required. As an example, a one-bedroom house would need a minimum tank fluid capacity of 300 gallons. If your house contains more six bedrooms, or you have five bedrooms and a spa, you’d multiply 150 by 6, and the total, which is 900, is multiplied by 2 to give you a minimum liquid capacity of 1,800 gallons.

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