My old cast iron box stove heated up my office quickly, but was hard to regulate, dried out the atmosphere, burned a lot of fuel, and cooled off quickly. Now, with a little masonry "hat" to capture the heat that was previously vented out the chimney, I heat up a few hundred pounds of bricks and mud which radiate a gentle heat into my office for up to 12 hours (depending on how much wood I use).
The surface temperatures are much lower than hot iron and (except briefly, at it's hottest), very huggable. In addition, I lined the firebox with brick, which makes the metal surfaces less dangerous, and increases combustion temperatures for a cleaner burn. Once hot (which takes up to about 10 minutes), there is no visible smoke coming out of the chimney. I typically burn it for less than an hour and have heat all day (I live in western Oregon, so it's not that cold). In my under-insulated cabin, the "hat" usually holds heat until the next morning. The stove was an old cast-off that now provides clean heat with minimal smoke. Oh, it also has a little "white oven" that we can bake in (note the wooden oven door on the lower R).
I don't have the technical apparatus to do the testing, but I do have neighbors with "approved" stoves that they load up with damp fuel that they allow to smolder all night long, clogging their chimneys with creosote and putting clouds of grey smoke into the blue sky.
Here's a quick video that gives you an idea of what's inside the heater. Most of the bits are recycled brick and tile, with a few new firebricks for good measure. The base I cast from special hi-temp cement.