I whole heartily disagree with the post above: Never Modify a Stove.
That might have been true a few years ago, but today with high liability and cut throat completion, stoves are not made as good as they could be, especially the lower priced ones.
What I am seeing lately is wood/coal stoves that have so many air holes in the firebox, that you could toss a horse through them. They do that now on account of liability. Years ago every one knew that you simply opened the draft a few moments before you cracked the door on an air tight stove or the sudden influx of air would cause a mini-explosion; back draft firefighters call it. That happened because the fuel was sufficiently heated, but lacked enough air to readily burn. This is what makes for incredibly long burn times on wood stoves. Today, stove manufacturers fear lawsuits and know if their fireboxes have air holes in them, the fuel will readily burn and there is no back draft potential or exceptionally high creosote build up. They really do not give one lick if you burn more wood, or send more heat up your chimney, as long as you buy their stove, they are happy. Now the more expensive stoves do care about their product and how well it burns, BUT their high price also takes into account higher liability rates.
In the perfect world, we would all be able to afford high end stoves and live happily ever after, however that is just not the case. It depends on your skill level of course, but since I have the ability to build US Navy Destroyers that have withstood mines in the Mediterranean, (and personally thanked by the Captain of the vessel for saving the lives of the crew by doing my job as a welder), I don't think modifying a stove that burns better is outside my skill set. Neither do I think it is outside the skill set of others.
In today's world where manufacturers know that people buy stoves based on price, they cut as many corners as they can on manufacturing them. My Vogelzang Pot Bellied Stove is an example. I have since greatly modified it and it is an excellent stove now. In every case the only reason the manufacturer did not do what I did to improve the stove, was on account of costs; latches for the firebox doors, seals on the doors, and automatic draft controls.
It could be argued that if a person has the skill set to modify a stove safely and efficiently, then they could build an even better one from scratch. That is a true point to make but why reinvent the wheel, when something simply can be improved upon? With the attitude; Never Modify a Stove, we would have never got out of the fireplace era. I am sure at one time people thought adding wood stoves to fireplaces was dangerous and ill conceived as well, and where would we be with that mind set. Modifying a stove is nothing to take lightly, but with some skills, research and investment, some spectacular results can be achieved.