This is a little rant about the BTU ratings of Pellet stove's. Before I begin let me say I love my pellet stove and have owned several. The BTU rating on almost all stoves is simply the max feed rate per hour multiplied by a BTU rate of a typical pellet (and I would guess not all manufacturer's use the same figure). So all told a 40,000btu unit can burn 40,000btu's worth of pellets in an hour. To that I say so what !
A number that would be far more useful would be the output btu's, and the actual heat exchange efficiency. Many stove makers list an "overall efficiency" which is a bit of a mystery, but to get the rating they are claiming I believe they take the combustion efficiency (nearly 100%), the electrical efficiency(nearly 100%), and finally the heat exchange efficiency and average them for the overall efficiency. So a stove with a heat exchange efficiency of 45% could have and overall efficiency rating of 81%. I had a quad santa fe and I am almost certain there was more and hotter air coming out of the exhaust then out of the heat exchangers. So of the 30,000btu's it could burn I was probably getting 15,000 or less. My Harman advance is much better, but it has two heat exchangers and uses less air then the quad. The exhaust of my harman is of far less volume and a lower temperature then that coming out the heat exchangers.
I am not bashing the quad, it was well built and ran great, but it was just very inefficient.
One of the most common questions on here is what size unit should I get, but an important factor is the stove efficiency because the units ability to keep up will be related to its output. This is particularly important because so many folks get these stoves to save money. Interestingly a Harman dealer I spoke with didn't know that the btu rating was not an output rating, so there are many involved in this industry who don't know it them selves.
I suppose the bottom line is selling and sizing stove's based on their btu input, would be a little like selling and sizing air conditioners based on their electrical usage.
I would be interested if any one else has noticed this, and is there reform on the horizon??
A number that would be far more useful would be the output btu's, and the actual heat exchange efficiency. Many stove makers list an "overall efficiency" which is a bit of a mystery, but to get the rating they are claiming I believe they take the combustion efficiency (nearly 100%), the electrical efficiency(nearly 100%), and finally the heat exchange efficiency and average them for the overall efficiency. So a stove with a heat exchange efficiency of 45% could have and overall efficiency rating of 81%. I had a quad santa fe and I am almost certain there was more and hotter air coming out of the exhaust then out of the heat exchangers. So of the 30,000btu's it could burn I was probably getting 15,000 or less. My Harman advance is much better, but it has two heat exchangers and uses less air then the quad. The exhaust of my harman is of far less volume and a lower temperature then that coming out the heat exchangers.
I am not bashing the quad, it was well built and ran great, but it was just very inefficient.
One of the most common questions on here is what size unit should I get, but an important factor is the stove efficiency because the units ability to keep up will be related to its output. This is particularly important because so many folks get these stoves to save money. Interestingly a Harman dealer I spoke with didn't know that the btu rating was not an output rating, so there are many involved in this industry who don't know it them selves.
I suppose the bottom line is selling and sizing stove's based on their btu input, would be a little like selling and sizing air conditioners based on their electrical usage.
I would be interested if any one else has noticed this, and is there reform on the horizon??
