Question: If a wood/gas/coal stove gives off heat all around (sides, top, even piping), how does an insert give off as much heat. I notice the BTU output measurements are almost identical for similarly sized floorstanding vs. insert units. Answer: Good question ! I've wondered the same myself. Truth is, the measurements you get on most units, especially gas, may not be accurate for one reason. I'm told that the efficiencies are calculated by a "stack" method, whereby the calculation is based on what goes up the chimney...not on the heat produced in the room. This can be misleading. Inspect the insert in question to see if the heat exchange system looks capable of doing the job. Inserts that extend out of the fireplace and have larger convection chambers are usually better at moving the heat.