lennox 90% in attic


I have a customer with a very erratic problem with thier furnace in attic. Its a Lennox G43UF-60C-110-08. The problem happens on only extreme cold days. I think something is freezing or slushing up in the furnace itself, maybe one of the vac. hoses or drain tubes that lead to the trap. There were some problems with the furnace drain that I corrected. They had it draining down an outside wall, uninsulated in some sections, no heat tape, and they used schedule 80 pipe. I thought for sure when we replaced it with schedule 40, rerouted it down an inside wall, reinsulated it and put heat tape on the pipe and trap, that that would solve the problem. But of course it acted up again, ball buster!!
This attic gets very cold. The water in the bucket I used to drain the pipe we replaced actually started to freeze. This is one of those green houses where everything is tight, and very little heat escapes through the ceiling that would help in this case. I think the problem is definately somewhere in the furnace with water freezing. If anyone is familiar with this furnace and this particular problem, I would appreciate some input. The temp here in NJ has gone up a little bit in the last couple of days, and the furnace is working perfect.
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wrote:

Its freezing somewhere probably the trap. Never install a 90+ in a unconditioned attic. Sounds like a hack job if you ask me.
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Yes it is a little hacky, I thought it might have been freezing in the trap too, that's why as I mentioned we insulated and put heat tape on the trap and drain line thinking that woud solve the problem, but it didn't. I think something is freezing in the furnace itself.

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Make a little room around the furnace, and drill a hole in the plenum, so some heat gets to the furnace?
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Christopher A. Young
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The condensate could be freezing inside the furnace thereby tripping the pressure switch., or any number of freezing scenarios. The furnace should have been an 80% in a cold climate attic using B- vent . You never put a condensing furnace in a place where it will get below 32 f. for extended periods of time.
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Just to be clear, I did not install this furnace. The people have been having problems and they called me to repair it. I agree to put a 90% furnace in an attic is not a good idea in a cold climate.
wrote:

The condensate could be freezing inside the furnace thereby tripping the pressure switch., or any number of freezing scenarios. The furnace should have been an 80% in a cold climate attic using B- vent . You never put a condensing furnace in a place where it will get below 32 f. for extended periods of time.
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wrote:

If they want it fixed tell them they need a 80% furnace not a 90+. Otherwise, to bad so sad.
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