Q: I've lived in a house with a working fireplace all my life. No doors, just a good, old-fashioned open hearth. But now my son e-mailed from college and said a professor told his class that fireplaces are a bad idea, energy-wise, and end up costing you more to heat the house. I can't imagine how heating with wood cheaper than oil costs me morethan using an oil furnace. If I didn't use the fireplace, I'd turn up the heat higher and use more oil. Before I bring this up in my e-mails with my son, I want to know the facts. Nobody I know has heard of this, so I'm hoping you know something about this. A: I share your love of fireplaces. I suspect that your son's professor was describing the fact that chimneys not only do a good job of drawing smoke out of the house but they also pull warm air out of the house. As warm air is lost up the chimney, equal amounts of cold air are drawn into the house from outdoors. That outside air enters through gaps throughout the house, such as around windows and doors, plumbing vents, wire pathways and more. That's why wingback chairs are traditional around fireplaces; they help protect people from the draft coming toward the fireplace. The result is a costly cycle, because your central heating system then works harder to replace the lost heat and to compensate for the incoming cold air. This phenomenon is at its worst on the very days we're most itching to get by the fire: on the coldest days of the year. So, you can see why fireplaces can lose more heat than they generate. Doors reduce heat loss but, seeing as you want an open fireplace, you can minimize the loss by making sure that the damper is shut when the fireplace isn't in use, after all ashes have gone cold. Find the sources of any cold drafts and seal them. Caulk around window frames and exterior door frames and use weather stripping on the doors too. In fact, sealing up air leaks is one of the most cost-effective improvements you can make to a house, whether or not it has a fireplace. A Home Performance with ENERGY STAR contractor can do a comprehensive job of air sealing, including key points between the house and the attic. You can find a contractor at www.efficiencyvermont.com/homeperformance . I hope this helps in your next e-mail to your son. Q: My daughter has taken a big interest in tropical fish. I think it's a great hobby and she's becoming very well-informed about it, but as the number and size of tanks increase, I can't help but wonder how much electricity this is using. Are there energy-efficient approaches to this hobby? If not, do you have an estimate of how much this adds to an electric bill? A: You bet. There are simple ways to minimize a fish tank's electric use. Keep it away from windows in the winter, set the thermostat as low as is healthy for the fish in the tank, and use fluorescent lights on a timer. As for how much of your daughter's hobby costs are in your electric bills, I'll give you an estimate for a 10-gallon tank with a filter, light and heater. That will typically cost about four dollars per month at today's electric rates. Costs go up as tank sizes increase. If you want to know more specifically how much power the fish tanks in your house are using, you can borrow a meter from Efficiency Vermont. Plug an electric device into the meter, plug the meter into the wall and you'll get your answer.