Before you rush out and get a new energy saving refrigerator, it’s important to understand how much energy your old fridge consumes. Why? For three reasons.

First, because you’ll be looking at Energy Guide labels on the new fridges, to find out which ones will cost the least to operate, and you might as well have an idea of how they compare to your existing refrigerator.

Second, if you want to replace your fridge mainly to save electricity, you may find out that you don’t need to. While today’s refrigerators are far more efficient than those of ten years ago, your fridge may turn out to be efficient enough that there isn’t a convincing motivation to replace it. You might save more money on energy, for the same investment, on weatherproofing or a new window or two.

Third, you may discover your existing fridge uses so much energy, that a refrigerator tune-up will save you money even in the short time before you buy the new unit. Things that can really help are: checking the gaskets for leaks or cracks, checking the temperature in both compartments (38-40F for fridge, 5F for freezer), ensuring the compressor and coils are dust free; and keeping good air circulation around the unit. Even if you find out that your old refrigerator is an electricity hog and you do a tune-up, you might find that the tune-up on its own will result in big electricity savings.

Your current refrigerator could easily be costing you $25 to $125 a year more than it should, and your new refrigerator may turn out to be less efficient than its ENERGY STAR label claims, depending on how you use it. But if you merely assume that a refrigerator uses what its label claims, you’ll be leaving a big opportunity on the table.

What if I told you that $20 could save you at least $40 a year, every year? It turns out that there is an inexpensive device that can do just what we’re after: measure the energy consumption of your fridge.

I bought a Kill A Watt meter about five years back and have used it to measure the energy consumption of many appliances in my house. I have also lent it to friends and family so that they could uncover energy savings of their own. These meters are available for about $20 and they measure how many kilowatt hours per day (kwh/day) an appliance like a fridge consumes. A measurement takes about three days, because a fridge cycles on and off, and only a longer measurement irons out the peaks and valleys of the refrigerator’s electricity use. But once you have that reading, you will know what your refrigerator consumes and you can start choosing actions to save electricity, or you can make a more sound decision about replacing your old refrigerator.

The Kill A Watt meter measures electricity use in several ways. The important readings for our purposes are time elapsed and kilowatt hours used. The Kill A Watt meter measures both of these values from the moment it is plugged in, so if you plug in the meter, then plug your fridge into the meter soon after, you’ll start to see how much electricity your refrigerator uses once a minimum of 24 hours have passed. Follow these steps:

1. Pull your refrigerator out from the wall. Unplug it and plug an extension cord into the wall outlet instead.

2. Plug the Kill A Watt meter into the other end of the extension cord, and the fridge plug into that. Leave the meter where its display is visible.

3. Push the fridge back. (You can just stick the Kill A Watt meter between the wall socket and the refrigerator, if that allows you to see the meter while you’re taking the measurement.)

4. Wait at least 36 hours to measure. Ideally you should wait 48 to 96 hours. If you keep pressing the red button on the Kill A Watt meter you will see readings for, among others, the hours and minutes elapsed, and the kilowatt hours consumed. You can compute kilowatt hours per day using the following formula:

kwh/day = kwh / ((hours/24)+(minutes/1440))

So if the final reading is 2.37 kwh and the elapsed time is 34h22m, the consumption would be 2.37 / ((34/24)+(22/1440)), or 1.655 kwh/day. Don’t wait more than four days to do your reading, because the time elapsed measurement wraps back to zero at 99h59m.

Most fridges are rated in terms of kilowatt hours consumed per year, so to compare your existing refrigerator with what’s available now, you can multiply the kwh/day result by 365. Our hypothetical fridge which we determined uses 1.655 kwh/day consumes 604 kwh/year. A 16 cubic foot Sun Frost fridge, in comparison – one of the most efficient refrigerators available – consumes only 254 kwh/year.

You can see how your existing fridge stacks up against new models by searching the www.energystar.gov database, for models that share features of your refrigerator. Fridge efficiency standards have gone up in recent years, and a fridge typically consumes more energy as it ages, due to worn gaskets, dust buildup on compressor and coils, wear and tear on the motor, and occasionally loss of refrigerant. And ENERGY STAR rated refrigerators must be at least 20% more efficient than the standard, so if you own an old refrigerator that was not ENERGY STAR rated when you bought it, you can see there is a big potential for savings, especially if you know your current consumption.

The efficiency requirement for refrigerators varies based on configuration (top or bottom freezer, side-by-side, or no freezer), volume, defrost features, and refrigerant type. And the formula is so convoluted that few people other than US EPA and DOE officials, and appliance company engineers, can really grasp it. So rather than quote the standard let’s look at a couple of examples.

An ENERGY STAR rated, 10 cubic foot, auto defrost unit that consumes 309 kilowatt hours per year, is 21% better than the minimum required for its category.

A 14 cubic foot partially automatic defrost unit that uses 254 kilowatt hours per year, is an amazing 36% better than the standard specifies.

As you can see, even for units that sport an ENERGY STAR logo, there is a wide range of efficiencies, and don’t forget that a large unit that exceeds the standard by 36% may still use more energy than a smaller fridge that exceeds the standard by only 20%, if the minimum standard for the two fridges is different. If you can choose a smaller refrigerator when you buy a new one, you will certainly save more energy.

Once you have measured how much electricity your refrigerator uses (it will probably be in the range of 400 and 600 kilowatt hours per year, depending on the size of unit, or even more if you have wasteful features such as side-by-side doors or an exterior ice and cold water dispenser) you can compare the consumption of your unit to those at the ENERGY STAR website, and see if it’s time to do a refrigerator tune up, or replace your refrigerator altogether.

If you’re in luck, you might discover that the model you have now is already an energy saving refrigerator. If not, at least you’ll have a great tool for seeing if your new fridge measures up to its billing.