Sump Pumps made Simple

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Ground water and your lovely home

house At the ripe old age of 53, my lovely wife and I moved from our two-story colonial to a ranch style house with a full, 1500 square foot, unfinished basement, and it came with a couple of maintenance issues. There are lots of big trees which dump a lot of stuff on the yard and house, and the property is damp. There aren't any bodies of water or streams, but rain and snow require ongoing work to route water away from the house. I do some of this work myself and hire contractors for big or complicated jobs. Remember, electrical, plumbing and other improvements may need to conform to building codes or other regulations. My house was built in 1964 in upstate New York. Your situation will be different in drier climates or on a shore, etc. Water hasn't changed much in the last 50 years, so most of this web page will be useful even for owners of newer homes. Let's consider the construction techniques and what happens to ground water near the house.

concrete block If there is groundwater, some will seep through a concrete block ("cinder block") foundation. There's nothing that can be done to stop that entirely, and in fact, the seepage takes pressure off the foundation. In other words, if the foundation were watertight, that groundwater would push on the walls until the water dried or until the walls caved in. Concrete blocks are porous and let the water seep slowly in. Concrete blocks are several inches wide, though, with "compartments". The water first seeps through the outer edges of the blocks and enters the compartments. Eventually, it seeps through the inner edges of the blocks, essentially into the basement. Usually, you don't see that water because of the way modern houses are built; more on that in a moment.

It's actually a problem to let the water sit in those compartments before slowly seeping into the basement because it raises the humidity of the basement and can cause mold. Small (7/16", I think) holes can be drilled through the interior edge of the blocks into the compartments at the bottom of the wall to allow the water in the compartments to flow directly in. This is good, because the water doesn't just sit there inside the blocks, but this will change the dynamics of your drainage system. Note that this involves scores of little holes in a typical basement, and you need a good drill and bit to do this accurately. A mold remediation contractor did this in my basement and covered the bottoms of the walls with a plastic paneling.

When groundwater is a concern, a "floating slab" construction technique is used. A sloped layer of insulation or tile or some material is laid, and the concrete floor is installed over that. Around the edges of the floor next to the concrete walls there is a narrow trench. As water seeps through the concrete blocks, it drips into the tile layer and flows down the slope to a collecting point. From there it is routed away via gravity or pumped vertically and then horizontally. In my case, the water is pumped to a storm sewer. The elevation of the entry into the storm sewer is higher than my basement floor, so gravity is not sufficient to get the water to the sewer.
floating slab

If your storm sewer or other runoff destination is lower than your basement floor, you can pretty much stop reading this page. The water will flow to a central drain pipe and then out of the basement to the sewer.

sump and inverter If your storm sewer is higher than your basement floor, the water needs help to get off that tile layer. The water flows to the collection point, gathers into a pipe and trickles into a pit called a sump pit. Without a pump, the water would enter the pit and then gradually back up into the pipe and up the slope of the tile layer under the floor. When the tile layer fills up, the water backs up into the trench, so if you see water in that trench, you're on the verge of a basement flood. As water continues to seep through the walls, it eventually overflows the trench and covers the floor. The height the water could reach depends on your specific geography.

In order to avoid the flood, a pump is inserted into the sump pit and a pipe leads vertically out of the pit, then horizontally through the wall and underneath the ground to the sewer. The sump pump has a switch with a "float" attached. As water flows under the floor and into the pit, the float is raised. When the float moves high enough, the pump is activated and the pit is emptied. In my case, a full pit is emptied in about 4 seconds by my 1/3 horsepower pump.

The amount of time it takes to fill the pit depends on the dampness of the exterior and the size of the pit. The pit is essentially a cylinder, so if your pit is 14 inches in diameter like mine (a relatively narrow pit), the volume of an inch of pit is Pi x 7" x 7" x 1", or 154 cubic inches. If the pit is 24 inches in diameter, the volume is Pi x 12" x 12" x 1", or 452 cubic inches. A gallon of water takes 231 cubic inches, so the narrower pit holds 0.67 gallons per inch and the wider pit holds almost 2 gallons per inch. We care about this because a sump pump will activate less often in a larger pit because it takes longer for the pit to fill. The less often a pump activates, the longer it will last. A good quality pump will last for several years, but its life will be shorter if a small pit causes it to work more frequently.

Backup options to keep pumping during power failures

I began my quest for a sump pump backup system within a year after I moved into my house, so as I write this, I'm using the previous owners' pump installation. For some reason, they set the pump on a chunk of concrete block in the pit. Possibly, this was done because the narrowness of the pit made it hard to reach all the way down to install the pump at the bottom. The problem is that water is pumped by the bottom of the pump, and since the pump is not at the bottom of the pit, some water remains after the pump stops. That water stays in the pit. We don't like standing water, no we don't. All pumps need to be replaced eventually, and I'll want that cinder block removed at that time if possible. The pump may have been raised a bit off the bottom to control the way dirt and other particles are sucked into the pump, which also affects pump life.

The pump in my pit is guaranteed for three years, and has a manufacturer's label from December, 2011. My pump sees a lot of action, as much as activating every ten minutes. After four or five years, I'll be nervous, and since I hope to eliminate that cinder block, I may then get a new pump even if the old pump is still working. It's easier to replace the pump during dry summer months than when it's wet and the pump has already failed.

Sump pumps are available at home stores and from other distributors. Zoeller pumps get good reviews, as do Liberty pumps in upstate NY.

Once you get your pump in place, a big storm will eventually come through and you'll watch that baby clear the pit. You wonder, though, what would happen if the power were to fail. As noted above, if the pump fails, the pit fills, the water backs up, the trench fills, and your basement floods. What to do? There are a number of options falling into two categories: (1) You can back up your pump with something that works without electricity, or (2) you can back up your power supply. You can do both.

There are pump systems that provide a standard electric pump along with a battery operated backup pump. There are two pumps, rather than just one battery operated pump, because DC powered pumps are not as powerful as electric pumps. The backup pump will not be as reliable over many pump activations, but it's fine for the occasional power failure.

There are water actuated backup pumps. These use the water pressure in your home's water pipes to create suction that clears the pit. Again, the backup pump is not as powerful as the primary electric pump, but it will work as long as you have water pressure.

If you can provide backup power to your electric pump when your usual utility power fails, you achieve similar peace of mind, i.e., the pump continues to operate. Backup power can be provided through generators or batteries.

First let me note some tradeoffs. An electric pump will eventually fail, and a backup pump provides a working pump while you get the primary pump replaced. On the other hand, generators and batteries can operate appliances other than just your sump pump. As long as you're aware your primary pump has failed, you have some time before the flooding begins. An electric pump will fail someday, no matter what backup options you use. When that happens, you'll probably need to disconnect the backup system while the primary pump is replaced, so it's not like the work can be done in a bone dry environment. You can back up your pump and your power if you want to spend the money and time. All these systems break down, and the more sophisticated they are, the more peace of mind they may provide, but the harder and more expensive they are to maintain.

Generac 8KW Generators run from a fuel source, usually gasoline, diesel fuel (including home heating oil), liquid propane or natural gas. They range from small, portable units to permanently mounted, whole-house units. A fully automatic, natural gas, 8000 watt, standby generator will cost you $6000 or more, installed. If you don't tie into your house breaker box and stick with a gasoline unit, you spend less money, but you can't run as many appliances and you need to keep fresh gas on hand, and you need to be home to start the generator.

Since I am a lousy plumber and do not want to get all that friendly with my sump pit, any backup solution that involves a new sump pump requires me to hire a plumber. All things considered, the cost of a new sump pump is about the same for me as a low-end backup power solution (excluding the cost of my existing sump pump). After much research, I decided to back up the power to my existing sump pump with a battery. Boaters and RV owners use "deep cycle" batteries to provide power for cooking, TV, etc. This web page is focused on similar, short-term residential backup power.

Transfer switch system A battery-based backup power solution involves one or more batteries, an inverter providing alternate power when utility power fails, a battery charger, cables, fuses and a transfer switch to choose from AC or inverter power to run appliances. A vehicle battery can be used, or a separate battery can be recharged from a vehicle battery. Common jumper cables can be used but won't perform as well as the heavier cables recommended for longer-lasting "deep cycle" batteries. Small inverters can be plugged into a vehicle cigarette lighter port, but these will not run a sump pump (as calculated below). Separate fuses may not be needed depending on the system. A transfer switch allows the system to run from AC (utility power) or DC (battery power), and that's optional, but without it you have to be present during a power failure to plug appliances into the inverter. You can also run appliances full time off the inverter, always drawing from the batteries that are always being recharged. This isn't "bad", but you'll need a more expensive charger and inverter as described below. For residential use, transfer switches are common. For marine and RV solutions, an AC source is often unavailable so a transfer switch may not be useful.

I do not want to use my car or manually engage my backup power. In March, 2013, I set up a dedicated deep cycle battery (Interstate Batteries DCM0090, 90aH) and an integrated inverter/charger with a transfer switch and heavy cables (Royal Power PIC3000). Over a few months, I tested the battery by running multiple appliances for extended periods. I may have over-drained the battery and it stopped taking a charge. In July, I was able to exchange it under warranty for an new battery, (Optima SC27DM, 66aH) The inverter is plugged into AC and the multi-stage charger is always connected to the battery, keeping it charged for when the AC power fails. The pump runs from AC when available, and from the battery when the AC power fails. I don't need a separate fuse. I can run other appliances off this unit with my sump pump, but each appliance drains the battery. My system should run my sump pump alone for several days off battery power, even if the pump is running frequently. In case of a long power failure, I could recharge my battery from a vehicle. My property has big trees and overhead utility lines, so I am legitimately concerned about an area-wide power failure once every 20 years that leaves customers without power for days. I can't run my water heater from my battery, but at least my basement won't flood.

To run several appliances during a power failure, the inverter should be in the 3000 watt range. Whole house applications, including a gas furnace, require at least 5000 watts. Inverters provide current with either a "modified sine wave" or "pure sine wave". Simple appliances such as incandescent light bulbs are not sensitive to the sine wave, but fluorescent fixtures and audio/video equipment require a pure since wave. Motors and pumps are not as sensitive as A/V equipment, but if operated permanently from battery power, a pure sine wave should be provided. If a transfer switch is used, appliances run off pure AC power most of the time, and an MSW inverter can be used during the occasional power failure (that's what I do, but I don't run my furnace and TV off battery power). The battery charger needs to be a multi-stage charger; this does fast bulk charging for a low battery and then reduces power to keep the battery topped off. A single-stage bulk charger can damage a battery if attached while the battery is fully charged. If there is no transfer switch, then the charger needs to be powerful enough to keep the batteries charged while they're being discharged to run the appliances. Chargers are rated according to DC amps, so the average DC amps of the appliances would be measured. The appliances don't all run continuously, so you need to estimate the amount of recharging needed to keep the batteries from going dead. In my opinion, it's easier to use a transfer switch and just use the batteries when AC power has failed, and that allows a smaller charger and, for most applications, an MSW inverter. Chargers are more expensive and complicated than transfer switches. PSW is more expensive than MSW.

Calculator! Battery backup power for residential applications

I found to be useful. If all you want to run is a sump pump, an MSW inverter/charger is great. If you're serious about running multiple appliances, assemble a PSW system from top quality components. Your appliances will thank you. I like playing with numbers, so here is my nifty calculator. My 1/3 horsepower electric sump pump has power requirements similar to a refrigerator. Inverters are rated according to the power (wattage) they provide, so I needed to determine the needs of my pump.

This program calculates power requirements and expected performance of a residential backup power system consisting of a power inverter that operates electical appliances using deep cycle batteries (similar to automobile batteries). Realistically, most homeowners will not run a home for days from battery power (or go off-grid) unless they have space for solar cells or windmills and lots of heavy, expensive batteries. My application is primarily to provide backup power for a sump pump.

? Battery voltage: 6V   12V   24V 36V 48V
? #1 amps: 110V   115V   120V :  used hrs/day =
? #2 amps: 110V   115V   120V :  used hrs/day =
? #3 amps: 110V   115V   120V :  used hrs/day =
? #4 amps: 110V   115V   120V :  used hrs/day =
? #5 amps: 110V   115V   120V :  used hrs/day =
? batteries, each amp-hours, will last
   Optional calculators to determine hours per day of appliance operation:
? Run for seconds times per day = hrs/day
? Run for seconds every minutes = hrs/day
? Run for minutes times per day = hrs/day

AC watts and DC amps: Electrical labeling on American appliances usually shows the AC amperes (amps) and AC voltage (volts). Multiply the amps by the volts to determine the wattage (watts). The electrical label on my sump pump rates it at 5.2 amps and 115 volts, so that's 598 watts. Total the watts of the appliances you wish to run on battery power. That total indicates the inverter needed to run AC appliances from DC batteries. You should overestimate your inverter needs to account for startup surges and future expansion. The wattage measured is for the "continuous" needs of the appliances, but each appliance draws additional power when starting up. The startup surge ranges from slightly more than the continuous draw for a light bulb, to a few times the continuous draw for pumps and motors. My personal recommendation is to account for a 4x startup surge. So, if you want to power 1000 watts of appliances, your inverter should account for a 4000 watt startup surge. I only want to run my sump pump and could probably get away with a 1500 watt inverter, but I went with a 3000 watt inverter (rated for a 6000 watt startup surge) to allow me to experiment with other appliances. Once I was in the 1500 watt range for a modified sine wave inverter, it wasn't much more expensive to bump up to 3000 watts.

To convert AC amps to DC amps, divide the AC voltage by the battery voltage, multiply by the AC amps, and add an inefficiency factor. The labeled battery voltage is typically lower than the actual voltage from a fully charged deep cycle battery, and the battery drops in voltage as it is discharged. For a 6V battery, this web page use 6.3 actual votes in calculations.
6V:6.3, 12V:12.5, 24V:25.0, 36V:37.5, 48V:50.0.
The inefficiency factor estimates the amount of AC-to-DC work done by the inverter. The inverter is powered by the battery in order to accomplish the inversion. This web page estimates the inefficiency at 15%. So, for my sump pump running from a 12V battery, the calculation is ((115V / 12.5V) x 5.2A) x 1.15 = 55.016 DC amps. Note that a DC appliance running off a battery does not suffer from this inefficiency because the inversion does not need to be performed. However, DC appliances are usually not as powerful as AC appliances.

Amp-hours: Once the DC amps are known, the calculator shows amp x hours, i.e., the power you'll draw from your battery rack per day. Ultimately, this calculator is intended to determine the operational life of your battery rack given your expected usage pattern.

Battery operation: Once you know how much power you're drawing per day, we can calculate how long a particular battery rack will last before the need to recharge. Batteries are rated for some number of amp-hours. My "group 27" battery (refers to the physical dimensions) is rated for 90 amp-hours. Battery specs are complicated and this is an estimate based on laboratory testing, but we can estimate the operational duration of an installation. If the number of daily amp-hours you need is greater than the total amp-hours of all your batteries, your operational duration will be less than a day. If the calculation shows a very short duration, less than an hour, you may not even be able to get all your appliances running.

Try calculating the load of a few light bulbs (.8 amps) for a few hours, along with a refrigerator (5 amps) for 12 hours per day, a microwave (9 amps) for .25 hours per day, a cable modem (1 amp) with wireless router (1 amp) for 2 hours per day, and charge up your laptop battery (1 amps) for a half hour per day, and your sump pump (5 amps) for 0.1 hours per day. You can see that running a whole house off deep cycle batteries for 3 days would require a large rack of 90aH batteries. After all that, you still don't have heat or hot water. Batteries weigh 50 or 60 pounds and cost a couple hundred dollars each. For the typical suburban homeowner, it's usually more cost effective (and space effective) to install a natural gas or liquid propane whole-house generator.

To run more than the occasional sump pump and light bulb, you should use pure sine wave inverters rather than modified sine wave. Consider a 5000 watt inverter (MSW $400, PSW $1500), along with batteries ($200 each), multi-stage charger ($300 for a big rack), transfer switch ($100 for a simple one, more to hook into your electrical box), cables ($100 per battery unless you can find some kind of bulk rate) and fuses ($50 each, probably need a couple). The charger will pull from your AC system to keep the batteries charged up (not prohibitive, a few dollars per month once the batteries are charged).

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