If your fireplace is too hot, you may notice that the room gets uncomfortably warm or that the fire burns too quickly. If you have a gas fireplace, you may also see flames shooting up the chimney. To check if your fireplace is too hot, hold your hand above the opening for a few seconds. If it feels uncomfortably warm, it's probably too hot. You can also use a thermometer to measure the temperature inside the firebox. If it's over 120 degrees Fahrenheit, it's too hot.