September 24, 2016

Assessing Home Energy Use

Calculating how much electricity you consume can help you decide which energy efficiency measures to take.

Q:I want to make my house more energy efficient, but am unsure what improvements it needs, and I don’t want to invest in a professional energy audit. What do I need, and how can I do my own energy audit?

A: Most homes, unless they were built with energy efficiency in mind, can benefit from improvements. The older your house is, the more likely you can significantly reduce your utility bills. Compared to most other forms of investment today, home efficiency improvements can provide a favorable financial return.

First, check with your local electric co-op to see if it has a low- or no-cost energy audit program. You may be able to get professional advice as a benefit of co-op membership, and many co-ops also offer free online home energy audit tools. Use the free Home Energy Optimizer at michigan-energy.org to get a comprehensive analysis of your home’s energy use, and find some cost-saving opportunities.

If your co-op doesn’t offer an audit program, first do a quick, simple analysis to determine how energy efficient your house is by calculating all the energy it uses throughout the entire year.

Keep in mind, this does not take into account the number of people living in the household or other factors that can significantly affect your energy use. For instance, if you have a small business in a home office, you need to have computers, printers and other electronics running the majority of the daytime, and often on most weekends.

To determine how much energy your house consumes annually, check your utility bills or other receipts. The calculation will be based on total British thermal units (Btus) of energy used. A Btu is about the amount of heat given off by burning a wooden kitchen match.

To convert various amounts of energy consumed into equivalent Btus, use the following factors: 1 kilowatt-hour of electricity 3,414 Btus 1 cubic foot of natural gas 1,025 Btus 1 gallon of propane 91,000 Btus 1 gallon of fuel oil 138,700 Btus 1 cord of wood 19 million Btus

After calculating the total annual Btus, divide this number by the annual sum of the cooling and heating degree days for your area—for the current year, not a historical average—which you can find via your local weather service. Finally, divide this number by the square footage of your house.

The number for most homes falls between 10 and 20, which means a variety of energy efficiency improvements will be beneficial. Greater than 20 means your house is very inefficient, and almost any improvement will help a lot. A number less than 10 means significant improvements will be difficult to achieve without serious investment.

Every house is unique, but indoor air leakage typically accounts for 35 percent of annual energy use. Check windows and doors for leaky gaps and joints, and check for gaps where the walls rest on top of the foundation, called the “sill.” Heat loss (or gain, during summer) through the walls and ceiling accounts for about 30 percent more. The remaining energy used is for other things such as lighting, water heating, cooking and electronics.

Holding a lighted stick of incense near the walls, windows and doors and observing the smoke trail can identify leaky spots. Move the incense around the edge and any place there is weather stripping or a caulked joint. It’s best to test this on a windy day. Also check for leaks at the ductwork seams.

If you have an all-electric house, turn on all the vent fans to create negative pressure indoors and then do the incense test. Do not use this method if you have gas, oil or any combustion appliances because backdrafting, in which depressurization will pull dangerous gases back into the home, can occur.

If you want to check for specific hot and cold wall areas that indicate air leaks or lack of insulation, Black & Decker offers a Thermal Leak Detector for about $40 (call 800-555-1212 or visit blackanddecker.com). It uses infrared technology, similar to professional models, to sense warm and cold areas. The sensor beam turns red on hot spots and blue on cold spots.

Check the accuracy of your central furnace/air conditioner thermostat by taping a bulb thermometer next to it on the wall. You may find the thermostat is inaccurate, and you’re actually keeping the house warmer or cooler than you think.

James Dulley is a nationally recognized mechanical engineer writing about home energy issues for the National Rural Electric Cooperative Association. If you have a question for Jim, please email jdulley@countrylines.com, or mail to James Dulley, Michigan Country Lines, 2859 W. Jolly Rd., Okemos, MI 48864. Be sure to let us know which electric co-op you receive service from. Visit dulley.com for more home improvement and do-it-yourself tips.