Let's say you're a wood stove manufacturer, and need to publish heating capacity numbers so potential buyers can compare your various models to each other and the competition. You know that people all across the country are going to see the same brochure. You also know that your potential customers are going to want to heat their homes in the coldest weather, which in North America occurs in January. So, you consult the National Average Weather Chart at http://www.infoplease.com/ipa/A0762183.html to see how cold that is. Here's what you find out: The average January temperature in Seattle, WA is 40.9 degrees. The average January temperature in Mount Washington, NH is 5.2 degrees. Obviously, your stove models aren't going to heat the same size homes in both locations. So, let's say you have produced a stove with a lab-verified absolute maximum output of 97,000 btu/hr. You know that people in the real world aren't going to burn that stove wide open all the time to achieve that output, but you need to give them some basis of comparison to your other models (and the competition), so you publish that number in your brochure, being sure to label it as a "peak" or "maximum" number. Let's say you've also found that this model will heat a well-insulated, single-story, 3,000 sq.ft. house with 8-foot ceilings in Seattle. You publish "heats UP TO 3,000 sq.ft." in your brochure for the same reason. trusting your dealers to interpret the adjustments necessary for their climate zones and for the particular houses to be heated. All manufacturers do this, and it does provide a valid standard of comparison from one model to another, when properly interpreted. I've noticed when people ask the forum about wood stove sizing, some members respond by asking about the house, and where it is located, like a good, experienced dealer would do. Others respond with blanket statements like, "The manufacturers' numbers are crap: reduce them by half." I can testify from personal experience that a homeowner who follows the latter advice and puts a non-catalytic, EPA approved woodstove rated to heat up to 3,000 sq.ft. in his 1,500 sq.ft. well-insulated, single-story house in Bellingham, WA will find that, if he operates the stove at secondary ignition temperatures as he's supposed to do, he's going to be enjoying his fire from out in the yard. By the same token, as recently posted on the forum, a homeowner with the same stove installed in a partially-insulated walkout basement in a two-story, 3150 sq.ft. house in MI might find that stove not quite up to the task. Not trying to start anything here, just suggesting that people come to the forum for good advice, and we should take care to provide just that.