How-To Determine the electric load of your house

by andrewodom on June 20, 2011 · 10 comments


The electrical load of the house is the total power consumed per day by all the appliances and electronics in the household.

While the electrical load is based on the wattage or maximum power draw of each appliance in the house, it also takes into consideration the average amount of time each appliance is used for in a day. Electrical load is calculated in watt-hours or kilowatt-hours, which describe the power consumption over the course of an hour. Understanding your house’s electrical load helps you identify and control large areas of power consumption. It also points to any modifications that may be required by your electrical system.

Know what you want to calculate. This can seem difficult but it’s really not too hard once you learn the terms. Most electrical appliances are rated with watts, while some use amps. To convert amps to watts, multiply the number of amps by 120. You do this because U.S. home electric outlets use 120 volts, and volts multiplied by amps equal watts. The number you want to find is how many kilowatt hours (kWh) you are using. That is what you meter reads and what you are ultimately billed for.

Create a log of what electrical appliances you use and how long you use them at a time. Keep in mind things that you do not actively (or regularly) control like heating or cooling units, water heaters, freezers, and refrigerators. Make a list for 5 straight days of all the appliances you used, to find a good average on each.

Check the labels on your electrical appliances. This is a start to calculate your electrical load and is a good way to get an idea of how much power each appliance uses. One thing to remember is that the number on the label is the maximum watts that appliance will use in an hour, so a refrigerator for instance will only use a small amount of power unless the compressor is running at which time it will use closer to the maximum power.

Estimate the amount of watts you use per appliance a day. If you need help for appliances like heating and cooling units, water heaters or other passive appliances, you can find many estimations on the Interwebs.

Calculate the kWh use for each appliance. The formula for kWh is watts multiplied by hours used and then divided by 1000. For instance, a 100-watt light bulb used for 10 hours would use one kWh.

Add all of the kWh totals from your appliances to get an idea of your electrical load that you use every day.

If you want to be incredibly specific you can use a watt-meter to get a better idea of how much electricity individual appliances use. A watt-meter will connect between your appliance’s plug and the wall outlet and it will tell you how much electricity the appliance uses over time.

I would also advise that if you want to convert your findings into actual overhead expense you need to either refer to your electrical provider’s monthly statement of phone them to find out the actual charge for kWh. The rate can vary greatly from zip code to zip code. Your bill might have multiple kWh rates (one for “delivery” and one for “fuel”), and in that case you should to add up them all up to get the total kWh rate.  Most rates are tiered, meaning the higher your use, the higher the rate.  When we did this for The Bungalow we entered our highest tier into the calculator (yes, we have a tiered system), because I realized the energy we could save would also save us money at the highest tiered rate.

Did You Know?

…an electric clothes dryer uses on average 4400 watts?
…a refrigerator can use upwards of 700 watts?
…a dishwasher can use 3600 watts?…a refrigerator can use upwards of 700 watts?
…a laptop computer uses 40 watts when plugged in?
…a 42″ LCD television uses nearly 236 watts?
…a coffee maker uses 900 peak watts?

I bring all this information to our attention as we here at the r(E)volution continue building and refining our solar power needs. We are looking at a grid-solar combination system but it will help us greatly if we choose appliances and light fixtures and the like with total wattage in mind.

What about your home? Do you keep energy consumption in mind? Is your monthly electrical bill out of hand? Do you wish you knew how to bring down those prices?

  • http://twitter.com/givmo Givmo

    We’ve been helping the people at ThinkEco (http://www.thinkecoinc.com/) test their product; it’s a lot like the watt meter you linked to but with a web interface for seeing live energy usage and energy usage over time as well as creating schedules to automatically turn things off an on. It’s a really nifty little device that exposes a lot of interesting, otherwise hidden, energy usage patterns. For example, when laser printers are on but not in active use, they cycle through periods of high energy usage just to keep the toner warm. It’d be great if all appliances had a publicly available graphs of typical energy usage; it’s much easier to save energy when you actually know what/when energy is being used!

    • anotherkindofdrew

      That sounds amazing. Are there plans to bring it to the market soon? 

      • http://twitter.com/givmo Givmo

        Yea it is really cool! I think they are currently doing pilots with businesses/organizations. I’m not sure when they will be  available in normal stores unfortunately.

  • Luke Rademacher

    anyone know of a device or apparatus that allows appliances to be plugged in but not allow em to drain/use energy until the appliance is needed – like for toasters, microwave ovens, coffee machines, blenders/food choppers, or even radios/stereos, televisions etc? sometimes its annoying to plug in and unplug stuff I am not using right at the moment – like my tv loses its settings anytime its unplugged.

    • anotherkindofdrew

      Not that I know of Luke. In regards to your TV, it would still lose its settings if it is receiving no power. I think you are talking about something that would act as a throttle or a governor. But other than a powerstrip (which would still pull phantom power) or unplugging, I really don’t know.

    • http://www.facebook.com/profile.php?id=576916498 Andy Hawkins

      It’s called a power bar ;-) but seriously, and sadly the answer is no. Modern devices seem obsessed with two things, telling us the time and storing settings data in a way that cannot be powered by an internal battery or capacitor. We don’t need everything in our house to tell us the time the way our home theater, dvd, microwave etc does but doing so requires the unit to be plugged in and drawing phantom loads 24×7. If our PC’s can keep their internal settings and clock powered by a small battery maybe we should be asking our home entertainment manufacturers why their systems can’t?

    • http://www.facebook.com/abel.zylzimmerman Abel Zyl Zimmerman

      There are some switching devices out there, but they are not specific to home appliances, and thus would take a bit of tinkering to get up and running. Therefore, it is probably easiest to look for appliances that do not have phantom electrical draws. People who use off-grid solar systems are quite preoccupied with this concern, so this is a good place to go for reference. The Backwoods Solar catalog has some nice tutorial information within. And the Backwoods folks are really wonderful: http://www.backwoodssolar.com. 

  • http://www.facebook.com/profile.php?id=576916498 Andy Hawkins

    My monthly power bill in my “big” house, (which isn’t really that big at 30′ x 49′ and only a single) it totally out of control, by far the biggest contributor though is heating. I have electric baseboard heaters and the house isn’t greatly insulated which up here in the Canadian Maritimes adds up to a hydro nightmare. Strangely enough this is not my first trip down this path, the first house I rented in town here had $650 hydro bills in the winter and $70 in the summer. After installing a woodstove (something I hope to be doing here shortly in the big house) the winter bills went down to $90 a month. I plan to heat my tiny house with wood as well and will be curious to see just how much wood it will need.

    In the meantime I’m trying to work out what appliances will make it to the tiny house and which ones will be electric, and which will be propane. Once I have that, with such a short list it should be fairly straight forward to work out my electrical requirements.

    The one question I keep coming up with though is if anyone is doing a totally off grid solar setup on a tiny home, and if so what issues, if any, are they coming up with when it comes to storing the electricity?

    • anotherkindofdrew

      Totally off-grid. Good question Andy. At this time I don’t know of anyone TOTALLY off-grid. I think adjusting to life in a tiny house is overwhelming enough at times that adding that to living totally off-grid would just be too incredible. Most people I know are doing it in steps. 

    • http://www.facebook.com/abel.zylzimmerman Abel Zyl Zimmerman

      Using a battery bank matched to your solar array (and climate) is a pretty established practice. If you have propane available, use that for as many appliance needs as you can. This will make the cost of your solar electric system manageable (but still not uber-cheap.)

Previous post:

Next post: