To make the most of interactive online green tools, gather information about your home. For the basics, you will need to know the amount of electricity and heating fuel you use (either by the month or the year).

If you don’t know your energy data, contact your utility companies. They should be able to provide you with the amount of fuel (oil, natural gas or propane) that you used last year as well as the number of kilowatt hours (kwh) you used either by the month or the year. Note the price that you pay per kwh.

For a general idea of square footage, measure the length and width of your house. For example, a two-story house with an unconditioned basement might be 25 feet wide and 40 feet long. Multiply those numbers to get one floor’s square footage (25 x 40 = 1,000). Multiply that number by the number of floors of conditioned space (1,000 x 2 = 2,000) to get an approximate figure.

Check your water heater, refrigerator, stove, clothes washer and dryer for such information as age, estimated amount of energy consumed, size, brand name, model number and any variable settings such as temperature on the water heater.

If you have a basement or crawlspace, check if your ducts are sealed. For a quick gauge of how leaky things might be, put your hand where two pieces of unsealed ducting connect when the furnace or central air conditioner is running. You may be able to feel the air escaping and not getting to the intended rooms.

If you purchased your present windows, look up the paperwork. Note their age and frame composition and whether they are double pane or have low-E argon gas. Count how many windows you have, get their approximate sizes and note which directions they face.

If you can, check the depth and type of insulation in your attic. For the home office, check your paper supplies and try to calculate your monthly or yearly use.

Having this information will let you take more advantage of the online tools and get more customized answers to your “what if” questions.