Where do you use the most energy?

Where do you use the most energy?  Is it heating your home?  Powering the refrigerator? Heating water for showers and dishes? Powering your entertainment center?  In order to really understand how you use energy, you will need to install some sort of home energy monitoring system like the TED-5000, but you can extract an amazing amount of information from just reviewing your energy bills, e.g. natural gas, oil and electricity.

We have been logging our energy usage and costs since before we bought our home.  What can I say, Alicia likes tracking things and looking at data.  This is very simple to to do, she just maintains a spreadsheet where she puts in information from the gas and electric bill each month.  We also track our bi-monthly water & sewer usage on the same spreadsheet, but today we’re focusing on energy usage.  If you want to do this your self, the data we find useful to record every month is:

  • Date (note it is usually a separate billing date for gas and electric bills)
  • Therms of natural gas used (you can always convert to cubic feet later)
  • Cost of Gas (total cost including supply and distribution)
  • What we actually paid (we have an average billing plan to even out the cost month to month)
  • Repeat for electricity substituting kWh for therms and Cost of Electricity for Cost of Gas

In terms of usage, most utility bills have the usage for the past 13 months somewhere on the bill, so even if you just have your most recent bill, you can get a year’s worth of usage data.  Oil is harder to track because you don’t get a monthly bill or a record of the previous year’s usage, though you should ask your oil company as they might be able to provide this history.  I was preparing for an energy audit at my church and our oil supplier was able to give me the past 12 years of data.  Chart 1 shows our energy usage for the past 5 years and the progress we have made in reducing our usage.

Chart 1: Overall Household Energy Use from 2005-2009
Chart 1: Overall Household Energy Use from 2005-2009

So, what sorts of things can you tell just from having your electricity and gas usage?  Here is what I figured out from our data:

  • Natural Gas usage makes up 58% of our total home energy usage (does not include gasoline for transportation)
  • Heating water is about 21% of the Natural Gas consumption over the year.
  • We have reduced our energy usage over the past five years by a total of 40% averaging about 10% per year. (last year alone we reduced energy usage by 23% and are on pace to do it again this year)
  • Air conditioning is about 10% of our annual electricity consumption
  • $ for $ in our home it has been better to focus on saving natural gas than electricity

To find out how I can tell this, read beyond the fold.

How to to figure out things from our energy bills:

Before looking at the bills and data, it is important to figure out what runs on each energy source.  In our home the things on gas are:

  • Heating Water (standard gas hot water heater)
  • Heating (High efficiency condensing gas boiler since Jan 2009)
  • Cooking (Gas range and oven) – minor
  • Clothes Drying (when not hang drying) – minor

everything else powered in our home runs on electricity including summer air conditioning with window units.

Heating Water – 12% overall energy usage

To tell what portion of gas usage is for heating water, look at the summer consumption. If you heat your water with electricity, then you will probably only be able to apply EPA estimates.

I take the lowest 3 or 4 months of the year and calculate the average, so that is June-September which works out to an average of 12 therms per month (shown) when we are not heating our house.  Of course this actually covers cooking, hot water and clothes drying, but based on Energy Star’s research, the energy used for cooking and clothes drying is negligible compared to the energy used for heating water.  So, applying 12 therms/month over the year, assuming that hot water usage doesn’t change significantly over the year,  works out to 144 therms of the 688 used, so water heating uses 21% of the natural gas in our home or 12% of our total energy usage.  This is consistent with Energy Star’s estimations that heating water accounts for 14% of an average home’s energy use. We’ve turned our water heater thermostat down to 120F, wash clothes (except cloth diapers) in cold and take short showers.

Here is our natural gas usage for 2009

Date Gas (Therms)
1/8/2009 134
2/8/2009 154
3/9/2009 120
4/8/2009 83
5/7/2009 37
6/9/2009 14
7/9/2009 13
8/9/2009 13
9/9/2009 8
10/8/2009 29
11/5/2009 35
12/7/2009 48

Heating – 44% of total energy use

We installed a high efficiency gas boiler in January of 2009 which has led to a significant decrease in our natural gas usage since then. We had air sealing and insulation done in November of 2009, and so far we’re seeing even more savings.  So far we’re on track for an additional 20-30% reduction in our heating bills.

The vast majority of our gas usage is for heating the house.  As shown below, we use about 12 therms of natural gas per month to heat water, dry clothes and cook.  That leaves the rest for heating, which with New England winters is a major expense.  In our case, after removing the 12 therms/month for heating water we are left with 544 therms or 79% of natural gas usage for heating.  When compared to total energy use in 2009, heating accounted for 44% of our total home energy use.

Air Conditioning- 4% of total energy usage

To estimate the energy usage for air conditioning, look at the non-summer months electricity usage when the ACs are not in the windows.

Here is our Electricity Usage for 2009:

Date Electricity
1/23/2009 514
2/20/2009 442
3/23/2009 467
4/23/2009 411
5/21/2009 405
6/24/2009 546
7/24/2009 520
8/21/2009 915
9/23/2009 652
10/23/2009 606
11/20/2009 554
12/22/2009 559

Figure out the average for the non-summer months, in my case 495 kWh/month.  Now subtract that from the summer months electrical usage and the resulting sum is the annual electricity usage for AC, 653kWh/year or 10% of our electricity usage and only 4% of total home energy usage.


Now that we know what several of our largest consumers of energy are in the home we can figure out where we should focus our attention to make the greatest impact and stretch our hard earned dollars.

Since heating makes up almost half of our usage, that is the key place to focus our attention, which is what we have done installing a high efficiency condensing boiler and air sealing and insulating our home. In terms of energy usage (and even just electricity usage) Air Conditioning is less than a tenth of our usage, so we should focus on other areas to look for savings. If we were in Austin, TX these results would likely be flipped with a very large portion of the energy usage going towards keeping the home cool with central AC.

The big energy use that demands more exploration is the other 90% of electricity usage, but that is for another post and requires additional tools like a kill-a-watt meter and TED-5000.

As you can see, with just two utility bills, a spreadsheet and a little time, you too can figure out what are the biggest energy users in your home and where you should focus your energy and money on reducing energy usage.  Start now, find your most recent electricity and gas bill and enter the data into a spreadsheet.  If you know how, you can probably log into your utility company and download the last few years of usage and billing data.  Don’t wait, get started now.

Happy Earth Day!


  1. Many institutions limit access to their online information. Making this information available will be an asset to all.

  2. Great info. and an interesting challenge! You have me wanting to break out the spreadsheets! 🙂

  3. Guys after watching and hearing this discussion about climate change and global warming we are missing the fact that some day for sure oil reserves are going to be exhausted. So what we are going to do then? Wind energy definitely can’t replace the fossil fuels. Nuclear power is too dangerous and can fall into wrong hands.I feel that solar energy if fully tapped can be used. Moreover a lot of job opportunities can be created as well. Yesterday I did a little bit of research about the solar power potential on FreeCleanSolar.com and found out very nice info. I am fully convinced that solar is the future. Any comments??

  4. Hi Maria,

    I think that solar will definitely need to be in the mix and that we cannot continue to rely on fossil fuels.

    I think the first priority needs to be efficiency. It has been shown time and time again that energy efficiency investments have the quickest return on investment and save the most energy per dollar invested.

    In terms of solar, I am a big fan, particularly of solar thermal which in New England could provide a significant percentage of the heating needs in the winter in addition to freely heated domestic hot water. But first, people should air seal and insulate.

    In utility scale implementations, a lot of research is being done on using solar thermal to generate electricity. I think this will be a big player in the coming years for the electric grid.

    I love solar PV as well and we are in the process of considering that for our home. Again energy efficiency can significantly increase the proportion of electricity generated by PV on a home or business.

    I think wind will play a big portion in the energy mix, perhaps as much as 20% overall because it is financially viable today and because once we start developing offshore floating turbines (one is already in production testing in Europe) then we can get more steady production of power. Also, with some of the cool energy storage ideas being developed at places like MIT, wind and wave energy can be used for base load power, something that historically, solar and wind have not provided.

    While I understand the risks of nuclear, we already have to deal with all the risks and issues, so leveraging that technology more fully with modern safety and protections will also play a role since nuclear already provides a significant portion of electricity generation for the world and can be used as a district heat source (co-generation) as well.

    Engineered GeoThermal energy is also a hot emerging technology that I expect to play a big role in the future too.

    So, I think solar will play a big part in the future, but we will not achieve our goals lowering the atmospheric CO2 levels and meeting the worlds growing energy needs without leveraging multiple complementary technologies including solar (PV & thermal), wind, wave, nuclear, geothermal and most importantly energy efficiency.


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