There’s nothing like getting cozy by a crackling fire on a cold night. But it may not be that warm OR healthy. Here are some facts about a wood-burning fireplace:

First: It won’t heat your house efficiently. Because most of the warmth goes right up the chimney with the smoke. Plus, heat rises, creating a draft, so a fire ALSO draws warm air from other parts of the house, and sends that up the chimney, too. So, unless you’re right by the fireplace, you may need a blanket to stay warm.

And that fragrant, woodsy smell? It’s actually pollution and a health hazard. Environmental experts say burning wood releases soot into the atmosphere and forms creosote. That’s a tar-like substance that ends up lining your chimney and must be removed by a professional. And if you don’t remove the creosote, you increase your chances of a chimney fire.

The final wood-burning fireplace fact: Once the fire dies out, you must keep the damper open for 12 hours to clear the soot out of the air. So your house will be an icebox all night long.

But, even with all those cons, there’s something special about a wood-burning fire. So if you’re going to light one, use hard woods, like hickory, ash, oak, and maple. They burn twice as hot and twice as long as softer woods like pine. And use glass doors to close off the fireplace – so less heat gets sucked out of the rest of your home… and less soot gets in your lungs.