Do You Need A Plumbing Upgrade Before Switching To Low Flow Toliets?

It's all too common for homeowners to change the water-using fixtures in their homes, such as sinks and toilets, without consulting with a plumber to find out if the new fixtures will work with the rest of the structure's plumbing. This usually turns out fine with newer homes, but if you're living in a home that's already a few decades old, there's a good chance that an upgrade like a new toilet could cause serious problems. Find out why low flow toilets and old plumbing are incompatible and how to make them work together.

Slow Flow

In older homes built before the 1992 decision to require new toilets to only use 1.6 gallons of water, the plumbers expected between 3 and 5 gallons of water to accompany each flush of the toilet. This is a dramatic reduction in the amount of water flushing waste down the pipes. In fact, many residential sewage systems were designed with flaws that were overcome by the amount of water flowing through the system. If you didn't notice a problem with slow drainage and clogged toilets until after switching to low flow models, it's likely a plumbing design flaw or age-related issue that is causing it.

Lack of Pressure

Most low flow toilets try to make up for the reduction in water by increasing the pressure of that water as it moves through the toilet and into the plumbing. This is supposed to help force the waste through the pipes to create fewer clogs, but it only works if the incoming water supply actually provides enough pressure for the toilet to use. The required PSI can range from 10 to 40 depending on the model and its features, so have a plumber test your home PSI before choosing a design with a high pressure requirement. You can contact a plumber at a company like Aurora Plumbing and Electric Supply, Inc.

Low Slope

One of the most common problems in the sewage lines of an older home involves a lack of slope. Today's building codes calls for a minimum of 1/8th of an inch of slope for every foot of pipe, while many older homes feature much less slope or even a negative incline that requires a lot of water pressure to clear. You can check for slope issues with the sewage lines connecting to your toilets by

  • Measuring the slope with a spirit level over the length of the pipe, which requires access to the drain pipe
  • Lifting the toilet up off of the seal and looking for standing water in the pipe below it
  • Hiring a plumber to check the level of the entire sewage system with a high-tech pipe snake.

While waste may have kept moving despite a lack of slope when there was a lot of water to push it along, it's going to become trapped in the pipes with a low flow toilet. Waste that sits in the pipes creates clogs, and even a little residue left behind leads to corrosion on older copper and iron pipes.

Fixing sloping issues is tricky because in most cases it involves replacing dozens of feet of sewage pipe at a time. The cost is even higher if the pipes are encased in the slab instead of open and accessible in a crawlspace or basement. If you're stuck with a low flow model but can't upgrade your plumbing, consider a design that offers a boost to move things through the pipes.

Boost Power

If you can't do much about your current plumbing and must install a new low flow toilet, look for a model with pressure assistance. These units house a small air compressor that gives each flush an extra boost of force to keep it moving in the sewage pipes. This feature can prevent clogs and help you make the most of older plumbing, but keep in mind that most models also rely on a high water PSI to couple with the blast of air and most older homes won't offer enough PSI.


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