Those seeking to convert their fireplace to gas have various options, each with advantages and drawbacks. (Sandra Leavitt Lerner)

Question: I’m the original owner of a 17-year-old townhouse with a wood-burning fireplace that’s seldom used because of the heat loss. The heating system and water heater run on natural gas, so I’m thinking of converting the fireplace to one that burns gas, as well. The fireplace is at the back of the townhouse, about eight feet from where the gas line enters the house.

Is this type of conversion advisable? What are my options (i.e., vented or ventless)? And what is the approximate cost for making this type of conversion? I’m hoping not to have to make a lot of structural changes.

— Alexandria

Answer: You have several options: a gas fireplace kit, a vent-free gas fireplace and a gas fireplace insert. None involve structural changes, but there are significant differences in aesthetics, energy efficiency, and effects on the air inside your townhouse. Having a gas line within eight feet is great, because basic installation costs often include hooking up to a gas line within 10 feet.

A gas log kit (about $850 installed, or maybe $200 more if you want remote-control flames) will give you the look of an open fire but not a lot of heat. The big downside is that installers must lock the damper into a partially open position. That guards against someone lighting the fire and forgetting to open the vent, which could flood your home with carbon monoxide. Having the damper open all of the time, of course, means that you’re losing heated or cooled air all the time — not the solution you’re seeking. To avoid that, you’d also need to install tight-fitting glass doors. Although these cost as little as $700, ones that are truly airtight start about $1,700, says Nancy Bart, a saleswoman at the Bromwell’s fireplace shop in Falls Church (703-207-9800; www.bromwellsthe
). So the cost of switching to gas logs could top $2,500.

A vent-free gas fireplace (maybe $850 installed) is another option. Because no exhaust would go up the chimney, you’d keep all of the heat in the room, and you could still have an open fire. However, all the combustion exhaust would also wind up inside, as would all the moisture released by the burning gas. That’s why vent-free gas fireplaces aren’t recommended when anyone in a house suffers from allergies, asthma or heart problems. Nor are they recommended as main heating systems; you’re only supposed to run them for three or four hours at a time, to keep the moisture and exhaust buildup to generally tolerable levels.

Finally, there’s a true gas fireplace insert (about $3,000). This solution changes the look of a fireplace, because you’re adding an insert, and it eliminates the option of having an open fire. But the look is still tidy, and the result is that you can enjoy the fire without worries. The glass doors are always shut because the fire chamber is sealed, with all of the combustion air piped in and the exhaust air piped out. This gives you energy efficiency and good indoor air, and it allows you to leave the fire running as long as you want.

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The Checklist: Read Jeanne Huber’s roundup of home-improvement tasks you should tackle in June.