Sump Pump and Ejector Pump

Many houses have a sump pump, and most newer houses (and some older houses) have an ejector pump.  This blog posts describes the purpose of each of these devices and explains some of the differences.

There’s a lot of water in the ground (of course – that’s why plants have their roots there!) and if any part of a house is below ground then that water wants to try to leak into the house.  And there are a couple of ways to deal with water.

You can try to block water out completely and not allow it to get anywhere it’s not supposed to be.  That’s actually not very easy – water will find a way, especially through an underground foundation that you don’t have access to for maintenance.  Or, you can give water a place to go where it can be controlled and won’t do any harm.  This is the point of a sump pump.

A sump is a pit dug at the lowest point of the house that gives water a place to go and collect before it can come through the foundation wall or through the floor slab.  Usually – but not always – there is also some buried drain pipe (usually called drain tile) running around the perimeter of the house and discharging into the sump.  This drain pipe is perforated so that water in the ground will leak into the pipe and wind up in the sump.

Ground water trying to attack the foundation finds its way into the sump.

At the bottom of the sump is a pump.  When the sump fills with water an automatic valve turns on the pump and pumps that water away, usually discharging outside of the house but sometimes discharging directly into a sewer line inside the house.

So ground water that’s trying to attack your house and ruin your basement instead runs into the sump and is pumped safely away.

An ejector has a completely different purpose.  An ejector deals with drain water from the house’s plumbing system, helping to get it out of the house. In Chicago and most of the older suburbs we have combined storm and sanitary sewers.  These cities use the same large sewer pipes to handle rain water and to handle the drain from your house (from sinks, tubs, showers, and toilets).  Here’s what it looks like, with a typical basement and the sewer line out in the street.  The house’s main plumbing drain pipe leaves through the basement floor, and all the drain water from sinks, toilets, and tubs drain by gravity out to the sewer in the street.

A typical older house with the main plumbing drain pipe going out to the sewer through the basement floor.

It used to be that when it rained very hard in Chicago and some of these older suburbs the sewers became overwhelmed with rain water and actually backed up into the basement through a floor drain.  As you can imagine, this was a huge nuisance and it could do a lot of damage.

During a heavy rain the sewer can get overwhelmed and floor the basement.

So the solution was to start using overhead sewers with an ejector pump.  Now instead of the main plumbing drain pipe going out through the basement floor it goes out through the foundation wall elevated a couple of feet.  All the drain water from the fixtures above this exit point can still drain out by gravity, but all the drain water from the fixtures below has to be pumped up (this includes the floor drain which now empties into the ejector sump).  This drain water first drains into the ejector sump, and when that fills up the ejector pump comes on and pumps this sewage up over a high loop where it can then drain by gravity.  An ejector pump is more powerful than a sump pump, and it’s able to grind up the solid waste from the toilet.

A typical newer home with an ejector pump.

Now if the sewers become overwhelmed by rain water, it would have to back up not just to the floor level but to a point about 6-8 feet above the floor before it could spill into the house.  And if that happens then we’ve all got a lot worse problems to worry about than basement flooding.

Now even if the sewer becomes overwhelmed it’s much harder for that sewer water to back up into the house.

A sump pump just needs a simple cover to keep out debris and to reduce the chance of the water evaporating into the house.  But an ejector deals with sewage – including waste from the toilet.  So the cover to the ejector pit needs to be sealed tightly to prevent those odors from getting into the house, and the pit needs to be vented to the outside through the plumbing system’s existing vent pipes.  So there are two pipes coming from an ejector pit – there’s the drain pipe and there’s the vent pipe.

A sump pump should have a battery backup system so that it can continue to work in case of a power outage.  This is when you’re likely to need your sump pump the most, during a big rain storm that might cause a power outage.  But it’s rare for an ejector pump to have any kind of battery backup system and it’s not really necessary.  But keep in mind that if you don’t have power then you don’t want to use any of the fixtures that drain into the ejector.  You’ll only want to use the fixtures at the first floor and above that still drain directly into the sewer by gravity.