I noticed that the downdraft Dutchwest 2477 has very good emissions, but relatively poor efficiency. Would it therefore be correct to conclude that downdraft designs in general sacrifice efficiency to improve emissions? Or am I just totally confused?
downdraft efficiency vs. emissions
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No, it's just that emissions and efficiency rating are allowed to be too vague. This is all being changed as we speak. In the near future manufacturers will not be allowed to use default numbers that make their products look more efficient than they really are. Currently only a few manufacturers post actual test numbers on their hang tags. Blaze King, and woodstock do on all of their stoves. A few others do, but not their whole line up. You will find that non-cat stoves will use this default number almost always, there's a reason for that!
No doubt downdraft stoves (if run properly) are highly efficiency in terms of both complete combustion and effective heat output. But while I can't comment on how the numbers are used for ratings, I do believe in general that downdraft designs sacrifice some effective heat output relative to other non-cats (and of course to cats), regardless of whether or not this improves emissions.
All modern stoves are designed to "lose heat" up the flue, in having a certain amount of uncontrollable secondary air flowing to the fire to maintain secondary combustion and ensure flue temps don't get too low (as they do in the pre-EPA "airtight" stoves). Because the downdraft design requires a good draft and very high re-burn temps in the secondary combustion chamber, I think it is probably common for flue temps to run a bit higher than with other stoves. That has been my experience, as well as that of others who have posted here.
So some heat is lost up the flue, above and beyond what other designs send up the flue. My impression is that you might require a little more wood in a downdraft to generate the same heat output as a burn-tube stove (and that burn-tube stove in turn could require a little more wood than a cat stove). On the plus side, I have a clean chimney!
All modern stoves are designed to "lose heat" up the flue, in having a certain amount of uncontrollable secondary air flowing to the fire to maintain secondary combustion and ensure flue temps don't get too low (as they do in the pre-EPA "airtight" stoves). Because the downdraft design requires a good draft and very high re-burn temps in the secondary combustion chamber, I think it is probably common for flue temps to run a bit higher than with other stoves. That has been my experience, as well as that of others who have posted here.
So some heat is lost up the flue, above and beyond what other designs send up the flue. My impression is that you might require a little more wood in a downdraft to generate the same heat output as a burn-tube stove (and that burn-tube stove in turn could require a little more wood than a cat stove). On the plus side, I have a clean chimney!
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