Will I be cooking my A-coil?

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Old 10-20-08, 02:59 PM
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Question Will I be cooking my A-coil?

Hello all, first post here and need a little help. I had an old Interdyne(?) 55/45 furnace that has the recalled gas valve burn up on me. I was lucky to have it not burn down my home, so, now that I still have my home, I need to fix it. I looked for a gas valve and they are around $200, give or take. When I opened my big oval portal door to the furnace, I could see the heat chamber/exchanger cracking in the corners leading to the inner portion of the back wall. There was one on each side about 4” long. I knew this back a year ago, but, being a double walled unit, I figured it was good for a little while. I decided to trash that unit completely and got me a Bryant 312AAV03070 (I believe it is). I am using this as a downflow and the unit sits on top of my old evaporator almost perfect, but, I am concerned as to how far the bottom of the furnace needs to be from the AC coil. It looks as if it is the same distance as the old unit (about 5-8” give or take) but the old unit was put in 1972 and this is a new 70k unit, MUCH hotter I am sure.

I have looked everywhere but can not find a “heat exchanger to AC coil distance” notes. I have looked EVERYWHERE and its getting real cold outside. Will this be enough distance or do I need some kind of transition duct work to raise the furnace?

Thanks.
 
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Old 10-20-08, 03:10 PM
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hvacman

I'm sure you meant the furnace sits atop the evaporator not the condenser. Five to eight inches from the furnace to the evaporator coil is ample.
 
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Old 10-20-08, 03:13 PM
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And here i was trying to sound professional, lol. Yes, you are correct. I type this up so fast, I was not thinking what did what.

But you say "ample", really? Just seems like a lot of heat so close? I am only asking because I want to learn, not that I am challenging. Just out of curiosity, does one measure from the edge of the exchanger as point "A" to what part of coil "B", or, is bottom of the furnace point "A", and then, where is point "B" ? It may not even really matter, but, again, I am just curious.

Thanks.
 
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Old 10-20-08, 05:49 PM
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Measurements

Measure from the highest point on the coil to the bottom of the heat exchanger. In an upflow application, the coil drain pan sits virtually on top of the furnace. If you are lucky there might be 1-2" between the heat exchanger & the coil.
 
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Old 10-20-08, 08:48 PM
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Wow, thats crazy! I did not think the coil could, would and should take that much direct heat.

Thanks.
 
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Old 10-20-08, 09:12 PM
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High Heat

It's really not much heat at all. Most gas furnaces only run around 120-140 at the plenum. Oil runs hotter & therefore the coil has to be at least 6" away from the heat exchanger.
 
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Old 10-21-08, 06:24 AM
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I thought a gas exchanger would be putting out around 260 degrees. Well, 140 isnt too bad, thanks Grady.
 
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