I'm sorry, but the Vogelzang is not putting out twice as much heat as the Encore or the Heritage. Stoves aren't magic. BTU ratings are useless.
Any stove can put out less heat if the input air settings are different or the wood is different.
There is 30 million BTU in a Cord of Osage Orange wood which calculated down means that 2.2 cu ft of the same wood has 515,625 btu's. so 119,000 Btu is not a stretch by no means.
I am not saying Omni test labs is right, its just that mathematical the numbers seem feasible.
The Btu rating is a combustion number not a number of how much heat your getting radiate out into your house there is a difference.
I think you're confusing BTU with BTUh, or the amount of energy versus the rate at which it's released. I believe most stove manufacturers are rating a stove based on how many BTU's can be released per hour, whereas you're quoting how many BTU's of energy a stove can hold and release over an entire burn cycle.
Joful, I think you hit the nail on the head there as think about this one step further, as we are going to have to figure this one out on our own as no stove manufactures are going to release their test documents for us to pour over and analyze, but anyhow If a stove is to be ran wide open to burn at is hottest output for max btu's , then the stove will only burn for lets say at its wide open setting for lets say 4 hours for example. So lets say the vogelzang example of 119,000 btu's at that 4 hours then the total btu's per hour for the wide open setting 4 hour burn would be 4 x 119,000btu = 476,000 btu so still you are in the ball park of the full load of osage orange which theoretically gives 551,625 btu in a 2.2cuft amount of wood. taking it one step further is if the stove rating of 76% efficiency is close then the 551,625 x .76 = 419,235 which is still in the ball park. Its in the ball park as I just used a 4 hour burn time as an example but what if the burn time was more like 3.5 hours when the stove is burning at its most wide open max air setting then the numbers would align up almost perfect for a 76% efficient stove.
So one more example is if the manufacturer of the stove that is rated 65,000 Btu , what maybe going on there is they set their input air settting for a 8 hour burn. You take 65,000btu number multiply it times the 8 hour burn time and you get a number close to the 551,625for osage orange example the best wood out there , the number you get is by calculating it is 520,000 btu.
So you get the picture real quick that it can be all in how you calculate the numbers.
Going back to what I said in my first post is to compare stoves, use the EPA tested Btu's numbers using the same type wood and the same settings for the stove.
Better yet you might use the efficiency ratings as that tells you how much heat you extracting out of the wood.
Looking at the big picture I think it was said previously by BeGreen and others that all these stoves EPA approved passed testing meaning they all are pretty close in efficiency. Its more about how you operate the stove and the kind of wood that makes the bigger difference in the performance of your stove. If your really interested in perfromance any of these stoves that are EPA approved will do exceptionally great on 3 year old season oak, hickory, Osage Orange.