it depends on the fire place. traditional fireplaces loose most of their heat via the chimney. ventless fireplaces loose 99.9 percent of their heat out of the front of the fireplace and into the home
Up the chimney. Fireplaces require a lot of air, which is drawn from outside the building. With an open hearth, much of the heat goes up the flue, and out of the building (having drawn cold air in from outside). A blower can spread warm air from the fire through the building, and hearth doors can limit (but not stop) air movement up the flue. Which is why wood stoves became so popular- they heat better than open fireplaces.
Chemical to heat
Radiation energy.
Some of it is though you also get convection an conduction heat transfer
Wood in a fireplace. When woods burns it gives of heat, a form of energy. Thus the wood has more potential energy.
If something is a good conductor of heat then it will lose heat slowly. If something is a poor conductor of heat it will lose heat quickly.
Better, in a heat efficient way, because there is no loss of heat, with a real one,you need to vent exhaust fumes and at the same time you lose heat. A real fireplace looks better but is less efficient.
The fireplace's heat is an example of radiation.
Fireplace
Heat cast forward out of a firepalce is called radiant heat and it the only usable heat that a fireplace can create The wasted heat that a fireplace creates is called combusion heat that rises up the chimney.
Check and see if your fireplace has heat vents on the sides or above the firebox, and that they are open.
You ARE going to lose heat up the chimney. Couple of things you can do to keep SOME of it in the room. Got a set of doors for the fireplace? They need to be open while burning, but can be closed as fire goes out, keep from sucking warm air out of the room. There are heat exchangers that are metal tubes with a fan. Tubes heated by the fire, fan pushes air thru the tubes, out into the room. The "Heatilator" style fireplaces have a heat exchanger built in to the fireplace. The heat exchangers are not cheap, and are still not as efficient as a wood stove.
The function that a fireplace fan serves is to distribute heat throughout the room that the fireplace is in. A fireplace fan is ideal because it's probably not safe to sit too close to a fireplace.
When you use the fireplace, the damper should be open all the way. If not, you probably will not get enough updraft and your house will fill up with smoke...not a good thing. When it is not in use, the damper should be closed...otherwise you will lose a lot of heat up the chimney.
The main thing that one should do to make sure that heat is not being lost through the chimney of a fireplace is to always close the damper when the fireplace is not in use. In addition, you can also use a fireplace door or cover to prevent additional heat loss.
radiation.
Radiation
Chemical to heat