Originally Posted By: dedwards
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I am not sure the stains are related to each other. The stains on the side of the plenum is mold stains very typical of air leaks around the tape and hard cast seams. The cold air leaks out and meets the warmer moist air normally found in these areas and condenstion forms, creating a perfect environment for mold to grow. the stain around the WH flue looks too looks very much like a leak around the weather skirt up on the roof. I find them installed too high up on the flue coming out of the roof and wind driven water comes in and runs down the sides of the pipe to the ceiling below. Its just a guess as I am not there to get the whole picture but I find these stains almost routinely. (Did one on Friday that had the exact same stain over the WH)
This looks like one of the furnace units that has a water jacket inside the furnace that receives hot water from the WH. Water circulates basically through a continous loop. Ive only seen one other but it works very efficiently and there is only about a 10-15 degree drop in the water temp. Once the water returns to the WH it is mixed quickly back to optimal temp. I have some literature on one made somewhere in Texas. Now I’ll have to dig it out because Im curious.