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Part II: Conservation FirstChapter 2. Find the Leaks

Reading Your Utility Bills Like an Energy Auditor

Turn a year of gas and electric bills into a baseline you can compare against later projects.

Difficulty
Beginner
Cost
Free
published

A bill is two stories printed on one page. The dollar story depends on rates, fees, and taxes. The energy story is the kilowatt-hours, therms, gallons, or hundreds of cubic feet. Projects change the energy story. Rates can rise in a year when you used less fuel and the dollar total still went up. If you judge the work by the dollar column alone, you will misread it.

This page builds a one-year baseline. The heat-loss sketch explains a cold night. The degree-day guide lets you compare two winters that were not the same winter. The PV guide should start from the kilowatt-hours you write down here.

Difficulty

Level
Beginner
Time
An evening with twelve months of bills
Skills
Adding a column and noticing summer versus winter

Cost estimate

Free

Use the utility's own history page if the paper bills are gone. You want units of energy, not a budget app's dollar chart.

Materials

ItemQtyNotes
Twelve months of each fuel1 setElectricity, gas, oil, propane. Wood is a separate estimate, by cord, if you burn it.
The unit printed on the billNotedkWh, therms, CCF, gallons. Do not assume.
A notebook page1Annual total, summer baseline, and what you think the baseline is.

Put the fuels in one language

You cannot add dollars of electricity to therms of gas and learn anything. You can convert each fuel into BTU if you want a single picture.

Unit on the billRough energy
1 kilowatt-hour3,412 BTU
1 therm100,000 BTU
1 CCF of natural gasAbout 1 therm, if your utility uses that convention. Read their factor.
1 gallon of fuel oilAbout 138,000 BTU
1 gallon of propaneAbout 91,500 BTU

A furnace does not deliver all of that to the rooms. An old gas furnace might deliver around 80 percent. A condensing furnace can be in the mid-90s. Electric resistance heat is nearly all heat, at a high fuel price. A heat pump can deliver more heat than the electricity's BTU, which is the point of the pump, and you must not divide that electricity as if it were a resistance heater. Write the equipment you actually have next to the conversion.

Separate base load from space heat

Plot the year. Electricity that stays flat is refrigeration, lights, plugs, and maybe a well or a dryer. A summer bulge is often cooling. A winter bulge is often electric heat or a furnace fan plus lighting. Gas that falls to a small summer value is space heat plus a base of water heating and cooking. The summer months, when the heating system is idle, are the baseline. Subtract a typical summer month from each winter month. What remains is a rough picture of space heat.

It is rough because showers get longer in January, because a pilot burns all year, and because a cold-climate house may still heat a little in a cool June. It is still the right picture to start from. One January bill is not a year. A mild winter is not your design winter.

Oil and propane arrive in lumps when the truck comes. The delivery is not the day you burned the fuel. If you can, compare full years from the same month, or read the tank and keep a log.

A year of fuel useTwelve monthly bars. Summer months sit on a low baseline. Winter bars rise above that baseline. The extra winter height is the rough space-heating portion.Summer baselineThe tall winter bars, minus the baseline, are mostly space heat
Summer months sit on a low baseline. The extra height in winter is the part of the bill space heat is likely to own.

What to write on one page

  • Annual kilowatt-hours, and the lowest month.
  • Annual gas or oil, in therms or gallons.
  • A summer month of that fuel, called the non-heating baseline.
  • Twelve times that summer month, subtracted from the annual total, called rough space heat.
  • The price per unit you would use in a payback, dated, because it will change.
  • Notes on anything odd: a house guest, a broken meter, an electric vehicle, a new well pump.

When you finish a project, compare the same calendar months only after you look at the degree days. A warmer winter will flatter a project that did nothing. A colder one will hide a project that worked.

  1. Collect twelve consecutive months

    For every fuel. Skip any chart that shows only dollars.

  2. Convert units you might mix

    Use the table, and write your furnace type beside it. Do not add electricity BTU to heat-pump heat.

  3. Mark the summer baseline

    That is hot water, cooking, and whatever else does not know it is July.

  4. Call the winter remainder space heat

    Roughly. Then take that number to the heat-loss sketch and see if the two stories can coexist.

  5. Date the price

    Payback math uses a price. The baseline uses energy. Keep them in separate columns.

Further reading

These links go to outside sources. This book cites them by link and does not copy their words or pictures.

General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.