Fireplaces give off radiation—but not the kind you’re thinking. Fireplaces give off infrared radiation, just like human bodies. Your mom and your fireplace give off the same radiation. Crucially, it is not harmful.
And, in fact, your fireplace emits less radiation than a microwave. This radiation is inseparable from the heating capabilities of your fireplace. To fully understand exactly how fireplace heating works—and also how it compares to heating from other appliances like furnaces and space heaters—let’s dig deeper.
How Do Fireplaces Provide Heat?
There are three ways heat can move: conduction, convection, and radiation.
A fireplace heats with all three.
However, traditional fireplaces primarily provide heat via radiation. In thermal radiation, emitted electromagnetic waves strike molecules and energize them, making them move faster and warming them up. There is no need for physical matter to exist between the heater and the heated, such as between the sun and the earth; the sun warms the earth via radiation.
The other two forms of heat transference, however, do require matter. And the distinction between them is what form of matter they use.
Convection, for one, is the transfer of heat via a gas or liquid. If you were to stand above a fire (or even put your hand over one) and feel warm air, that warm air would be heating you via convection. (which is why you place your pots directly above a fire on a gas stovetop; the fire heats the air, and the hot air rises and heats the pot.) Since hot air rises, directly above a fire will be the hottest spot. There, an object would be heated both by radiation and convection.
Whereas convection transfers heat through moveable matter, conduction is heat transference through solid matter. Touch the hot bricks around a fireplace and conduction will be warming you. You’ll notice that “conduction” and “conduct” are related words—and just as certain materials are particularly good conductors of electricity, others conduct heat very effectively.
Metal, for example, conducts heat well, which is why metal pots burn you when your potholders don’t, and metal utensils left in something hot can burn. Also, this is why metal objects are particularly painful to touch in winter. These are all examples of heat conduction through a solid medium. Conduction is a very efficient (most of the energy goes toward the intended purpose) but very slow way of heating something.
A wood-burning fireplace provides heat via radiation, convection, and conduction—in other words, with all possible methods of heat transference. However, most of the heat your fireplace gives to your home comes by way of thermal radiation.
Your fireplace’s convection heat is moving through the air, and hot air rises. So while your fireplace does produce a huge amount of convection heat, most of that heat goes straight up your chimney and out of your home.
Meanwhile, the conducted heat is mostly limited to what you feel if you are right next to the fireplace, physically touching the bricks.
Similarly, gas fireplaces heat your home primarily with radiated heat. Some convection heating also takes place but has very little conduction. Instead of stoking a fire, and instead of needing a steady supply of fresh wood, a gas fireplace is controlled through external means (the same as any other gas appliance), where you can control the level of gas output for maximum control over the strength of the fire. Since most of the heat is given off by radiation directly to the objects within sight of the fire, gas fireplaces heat the room they’re in much more effectively than they heat the rest of the house.
Electric fireplaces heat your home with an electric heating element or heating coil. Cool air flows into the fireplace from the room, which is then warmed by the heating coil and flows back out into the room, warming your home by convection.
Electric fireplaces are also convenient since they can be turned on or off with just the flick of a switch, versus needing to stock up on wood and then building a fire for each and every use. However, the downside to an electric fireplace (versus a wood-fueled one) is if your electricity goes out, so does your heating; a wood-burning fireplace will work no matter what’s happening with the rest of your appliances.
Are Fireplaces Safe?
We’re all aware of the fact that fire is one of the most dangerous things we interact with within our lives. Your home is the last place you want to have a fire. So it’s possible to make the argument that a fireplace—a box specifically designed to make fire inside your home—is a weird idea.
Is a fireplace safe? Well, fire is incredibly dangerous, and a fireplace means fire in your house—so the answer is, not entirely. Fireplaces are, in fact, dangerous. If used properly (and properly maintained), you can stay safe even while using a fireplace.
But there are always risks involved, and you always do have to be on your toes when using your fireplace and actively, intelligently working to make sure your fire is under control. In particular, please keep your chimney professionally maintained—according to the National Fire Protection Agency (NFPA), there are more than 25,000 chimney fires in the United States every year.
In addition to the obvious risk posed by a fire in the home, fireplaces also have health risks because of the smoke and the gasses they produce. Smoke can cause respiratory issues and lung cancer.
Burning gas and wood can also produce carbon monoxide—which, in a properly vented fireplace, is mostly sent outside. However, if your fireplace is not venting properly, this deadly gas can build up in your home without your notice since carbon monoxide is invisible and odorless. For this reason, a working carbon monoxide detector is invaluable to your home.
If you are concerned about pollutants from a fireplace, consider an electric fireplace, which releases no such fumes into your home.
Do Fireplaces Heat Efficiently?
Despite how cozy they are, wood-burning fireplaces and gas fireplaces are incredibly inefficient heaters. In a wood-burning fireplace, 80-90% of your fireplace’s total heat does not warm your home. Instead, it goes right out of your chimney. Of the heat wood-burning and gas fireplaces produce, most of what actually warms your home is radiation heat—but they are also producing massive amounts of convection heat, and almost all of that goes straight up the chimney and outside.
Additionally, the chimney is a year-round energy leak, letting heat out during the winter and letting A/C-cooled air out during the summer. For this reason, if you have a chimney, always remember to close the flue when not in use and make sure the damper has a good seal to minimize air leaks. It is not impossible for an active fireplace with active fire to end up cooling a room, with more indoor heat lost up the chimney than fire-heat added to the room (though this is not common).
When it comes to gas fireplaces, gas logs throw away about 75% of their heat due to the problems we’ve just discussed, while gas inserts are far more efficient because they are fully enclosed—thereby losing only 20-30% of their heat.
But by far, the most efficient fireplaces are electric ones, which lose only 1% of the heat they produce because they are not connected to the outside. So all of their heat (or at least 99% of it) stays in your home. And since they don’t create smoke or combustion inside your home, there is no risk of indoor pollutants. If you’re wondering whether an electric fireplace or a space heater is more efficient, well, they are essentially the same thing, just with different aesthetic designs.
Furnaces are another viable option, with up to 98% efficiency, as well as more effectiveness warming your whole house evenly than a fireplace. A fireplace’s heat radiates from only one spot and slowly leaks to the rest of your home, but a furnace sends heat to every room in your house.
However, there is the coziness factor: you’ll have to decide whether getting to read in front of a fire or if energy efficiency is more important to you.