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Re: how do I operate a Heat Exchanger

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Posted by George on March 21, 2004 at 06:26:24:

In Reply to: Re: how do I operate a Heat Exchanger posted by Harold hydronicnetwork.net on February 22, 2004 at 07:21:40:

Just a few comments on the subject:
Harold is most certainly correct about condensation and reduced draft! However, in some cases these considerations are not a big deal.
I installed an old oil heater (100,000 BTU)in a shop area at our non-profit Historical Association where the flue is short and all metal. This discarded heater had a burned out combustion chamber that I repaired and then lined with Cerafelt. The system runs very well and the improved efficiency of the chamber results in pretty high flue temperatures.
I have one of these Van Wert units (5') and plan to install it as soon as I get a motor and fan for it. My feelings are that this unit will improve the overall heating efficiency.
BUT, I would not install one of these units if I had a standard masonry chimney because of the likelyhood that the flue gases in the relatively cold chimney would get below the dew point and would therefore allow acidic (and perhaps combustible) compounds to condense on the surfaces. Such condensation in our short flue will be of no concern since it is so easy to replace.
Harold also stated that new heaters are much more efficient and have already undergone design improvements to wring as much heat as possible out of the flue gases.
Let me know the flue size, motor data, and fan blade size on your unit. This will help me to pick a replacement motor and fan for ours.
George

It is supposed to save fuel by taking the heat that is left in the flue after the furnace uses what it can. It is a bad idea, because it reduces the flue gas temperature that drives the flue gases up the chimney and can cause draft problems. It is an obsolete artifact left over from 40 years ago.

: If the furnace is so badly constructed that it can not extract the heat to the home on its own, it should be replaced. As almost all today's oil furnaces are better than 84 percent efficient, there is no longer a place in this world for such an exchanger, as it can only make serious draft and condensation problems.

: Remove it to be replaced by a good piece of sheetmetal vent.

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: Just a few comments on the subject: : Harold is most certainly correct about condensation and reduced draft! However, in some cases these considerations are not a big deal. : I installed an old oil heater (100,000 BTU)in a shop area at our non-profit Historical Association where the flue is short and all metal. This discarded heater had a burned out combustion chamber that I repaired and then lined with Cerafelt. The system runs very well and the improved efficiency of the chamber results in pretty high flue temperatures. : I have one of these Van Wert units (5') and plan to install it as soon as I get a motor and fan for it. My feelings are that this unit will improve the overall heating efficiency. : BUT, I would not install one of these units if I had a standard masonry chimney because of the likelyhood that the flue gases in the relatively cold chimney would get below the dew point and would therefore allow acidic (and perhaps combustible) compounds to condense on the surfaces. Such condensation in our short flue will be of no concern since it is so easy to replace. : Harold also stated that new heaters are much more efficient and have already undergone design improvements to wring as much heat as possible out of the flue gases. : Let me know the flue size, motor data, and fan blade size on your unit. This will help me to pick a replacement motor and fan for ours. : George : It is supposed to save fuel by taking the heat that is left in the flue after the furnace uses what it can. It is a bad idea, because it reduces the flue gas temperature that drives the flue gases up the chimney and can cause draft problems. It is an obsolete artifact left over from 40 years ago. : : If the furnace is so badly constructed that it can not extract the heat to the home on its own, it should be replaced. As almost all today's oil furnaces are better than 84 percent efficient, there is no longer a place in this world for such an exchanger, as it can only make serious draft and condensation problems. : : Remove it to be replaced by a good piece of sheetmetal vent.

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