Though aesthetically pleasing, traditional fireplaces are extremely inefficient, unhealthy and environmentally-unfriendly.
They lose over 90% of the heat they produce through the chimneys, and if there is no fire and the fireplace damper is left open, warm inside air will escape through those same chimneys.
And they also emit dangerous pollutants, in large quantities: CO, CO2, dioxin, arsenic, formaldehyde...
Some people like to argue that wood smoke has been around since our origins as human beings, which is true. But our antecessors did not live long enough or in air-tight modern homes, where the effects of smoke are a lot more dangerous.
Wood smoke contains complex microscopic particles that get into our respiratory system and aggravate heart and lung diseases.
Traditional fireplaces are a really bad choice.
To minimize their impact use only seasoned wood, which burns hotter and releases a lot less smoke; to ensure that the wood is really dry, make sure that it has been stored for at least five or six months.
The fire-building technique is also important; the fire should be kept hot, that is, with visibly high flames for at least 15 or 20 minutes, to allow the chimney to heat up and to avoid the smoke to drift into the house.
Also do not forget to keep the damper closed, when not using the fireplace, to prevent inside heated air from being lost up the chimney.
Anyway, these are just palliatives. They can't fix the raw fundamental problems raised by traditional fireplaces. If you want to keep using firewood, consider fireplace inserts instead of traditional fireplaces.
Fireplaces inserts are basically wood stoves converted to fit in existing fireplace openings, able to burn wood in a very efficient way. The level of emissions of certified units can be less than 4 grams per hour (instead of the 30 grams of traditional units). And they have a reasonable or good heat output, contrary to common fireplaces.
New energy fireplaces vs. insert fireplaces
Be cautious when buying. Pay attention to the distinction between factory-made fireplaces and insert fireplaces (stoves designed to fit inside existing fireplaces). Though the line between the two is now somewhat blurred, only the “stove” technology ensures good or reasonable results.
These “efficient fireplaces” come with a white tag (image at right), certifying that they are at least 70 percent cleaner than non-qualified models. But though they burn cleaner than traditional fireplaces, they are a lot more pollutant than EPA certified wood stoves and fireplace inserts and a lot less efficient than wood stoves and the fireplaces inserts using the new stove technology.
Most of the best wood fireplaces inserts are air-sealed combustion units, and they may include variable heat output and air boost devices for faster wood ignition.
The heat output of wood fireplaces
As said earlier, traditional wood fireplaces can lost about 90% of the heat they produce through the chimney. Their heat output is very low. And this really contrasts with the best fireplace inserts, which can reduce heat loss to 20%. Many of them are now able to heat rooms up to 2000 sq. feet (190 m2) or more, with an average burn time of 8 hours.
Be cautious anyway. Do not oversize; manufacturers often overestimate the efficiency of their inserts/wood stoves and assume conditions that do not exist in practice, like zero moisture content wood.
The insert should be chosen according to the size of the room, to avoid overheating problems. And do not forget that a good installation is critical for performance, as much as seasoned wood.
Prices & Alternatives
Though cheaper than traditional metal fireplaces, qualified wood-burning inserts aren't exactly a cheap option; expect prices to range from $2,000 to $4,000.
And do not forget alternatives to them: gas, pellet and decorative electric fireplace inserts, or direct-vent wall-gas heaters. Some of these last alternatives are a lot cheaper, and burn cleaner and more efficiently than wood.