Q&A Catalytic convertors: Do they REALLY increase the heat outpu

QandA Posted By QandA, Nov 24, 2007 at 5:42 AM

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  1. QandA

    New Member 2.
    Staff Member

    Nov 27, 2012

    Though I understand the concept and principle of catalytic convertors, I have always found it difficult to accept that they result in more heat being supplied to the desired (heated) space. Oh, I won't argue that they don't affect the combustion efficiency (burn gases more completely) and thus improve air quality, but given their typical placement in the discharge path (oftentimes, external to the stove itself) it would seem to me that in order to recover that extra heat, a substantial increase of heat exchange surface, such as a four-foot run of stove pipe downstream of that device would be required. That, IMHO, simply is not typical of all installations. It seems as though stove retailers turn a deaf ear to my position on this....but then, that shouldn't surprize me....afterall, they've got a product to sell. I was wondering if any folks here have any thoughts on this matter.


    That assumption is reasonable. Getting extra heat would depend on a number of additional factors such as the strength of the system's draft and materials surrounding the combustor.

    The company I was affiliated with for years used a high temperature refractory silicate material around the combustor. This was used to encourage a high temperature environment for better combustion (combustion efficiency), protect the outer materials from damage, and to invite better residency time to allow other surrounding materials (in our case--cast iron)to capture this heat and send it out into the room (transfer efficiency). That is why a stove made today has an overall efficiency (combo of combustion & heat transfer efficiencies) in the very high 70%, versus a stove made in the late 70's / early 80's which was about 60%.

    The design of a combustor must be in the "discharge route" as that is where the volatile gases are heading. You must have the combustor as close to the source of heat as possible as that is when the gases are "ripe for the picking" for better secondary combustion. At that time, you must design a fairly simple route (heat exchange) for heat transfer without creating a system bottleneck. And, in conjunction with this design, you cannot take too much heat from these gases or else you will slow the draft down. When draft slows, you are dead in the water. That's the balance one must find in combustion & stove design.

    My experience in testing stack temperatures 3 feet above the flue collar is that I did not find a substantial difference (50-70 degrees Fahrenheit) between a stove made in the late 70's, and one made in the 90's. This was done in the lab, and in my own home. Plus, the chimney was cleaner, less wood was used seasonally with the same-to-more-heat provided, and no smoke left the chimney. So, where did the heat from these spent gases go? In the house, my friend, in the house. The technology works without a lot of apparatus attached. Hope this helped.
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