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Old 01-24-2014, 02:01 PM   #31
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Natural gas furnace combustion air intake question.


Hmmm, still- something is effecting the primary air making its way for the combustion process which is why it works when you remove the door. Id be very interested in hearing what the service tech finds when he looks at it.

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Old 01-24-2014, 02:03 PM   #32
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Natural gas furnace combustion air intake question.


Personally I think your major problems ( based on similar experiences ) are:

1) need that tee

2) get the furnace elevated 1/2" from back to front so water drains out faster and it helps to be sloped from left to right as that is where the water leaves.

These furnaces can be finicky with how fast they drain and when that does not happen it backs water up into the secondary heat exchanger and causes press switch problems. If that does not solve it then get the switch replaced as it may be faulty and yeah a 2 pipe system is always better but MUST be done according to Nordynes specs. If not then you have exhaust recirc into the intake and more press switch problems. If no water came out that port and no sloshing sounds then you don't really need that hose.
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Old 01-24-2014, 05:57 PM   #33
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Natural gas furnace combustion air intake question.


Right after the furnace finishes a heat run, pull the cap off the bottom port of the inducer, and see if water runs out.
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Old 01-26-2014, 08:52 PM   #34
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Natural gas furnace combustion air intake question.


Beenthere: Checked bottom port on inducer assembly just after a cycle, and still nothing came out. No sloshing.

Just a quick update. Took the PVC condensate drain pipe out of the pump and stuck the end in a jar. The pipe has put out no water all night, in fact bone dry. Only blowing warm air.

That can't be right, can it?

Furnace is level front to back, and about 1/2" high on the drain side. I can't fix that by myself the way they have it set up [Sheet metal duct out of top of furnace jammed against floor joists. Large boards below furnace can't be removed without destroying drip pan.] Will call them tomorrow.

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Old 01-27-2014, 10:00 AM   #35
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Natural gas furnace combustion air intake question.


Called installer. He said the pvc pipe drain is only for AC. AC coils sit above the furnace. He says heat exchanger drain is a plastic tube inside the furnace.

He thinks it is the pressure switch itself and is going to replace it. I'll update later, in case someone is having similar problems.
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Old 01-27-2014, 10:25 AM   #36
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Natural gas furnace combustion air intake question.


that plastic drain tube needs the open tee and that is why I mentioned you can buy it and plastic fittings with barbs to do the job. the furnace will work w/o slope but it is better if it has.
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Old 01-27-2014, 10:54 AM   #37
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Natural gas furnace combustion air intake question.


Thanks Yuri, I'll tell him when he gets here.
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Old 01-27-2014, 11:22 AM   #38
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Natural gas furnace combustion air intake question.


Yeah, Try HARD to convince him to cut that hose and put a tee in it. I have had to do it on other furnaces and it is a pain in the butt but necessary. Needs an open end to siphon better like a sink or any other plumbing drain. Few techs do it or understand it and it is standard procedure on all Lennox furnaces. If he laughs at it or does not agree then it is easy to DIY. Plus the hose should be above the pump water level like you read elsewhere. These PVC plastic fiittings from HDepot or any plumbing store are what I use
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Old 01-27-2014, 04:47 PM   #39
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Natural gas furnace combustion air intake question.


I am a nordyne installer and the installation looks textbook. You have a drain installed on the flue as well as the collector box. The location of the pump is fine and the drain is open(vented) via the vent pipe. Im betting on icing as the problem. The pressure switches are very temperamental on these furnaces. Any icing on the discharge of the flue will restrict it enough to cause the pressure switch to trip. Also, the freezing of the drain pipe will cause the safety switch in the pump to break the R terminal on the furnace. Next time it goes out, get the error code on the board and see what its telling you. Good luck
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Old 01-27-2014, 05:42 PM   #40
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Natural gas furnace combustion air intake question.


I have had drainage problems with Ducanes and AireFlos where they have that horz soft pipe running thru the fan or elec compartment. It gets dips and airlocks and the open Tee helps a lot. with a clear hose and the door switch taped closed I could actually watch the draining problem and learned that technique the long hard way. Probably with 3 inch venting they would never have that problem. I don't usually see 2" on anything over a 70M BTU so 2" seems iffy and not what I would use. 3" is so large it never ices up.
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Old 01-30-2014, 11:07 PM   #41
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Natural gas furnace combustion air intake question.


Update...

The fellow came two days ago and replaced *both* pressure switches. Said he had been talking to fellow HVAC experts in the area and they were pretty sure that was the problem. Next day same trouble. Pressure switch open fault again.

And yes, he completely dismissed the ideas of tilting the furnace and providing any vents on drain lines.

Rather than try to force him to do those things, and then take the chance it would not help, I decided to just do it myself. I may still need to call him again after that, so I don't want to burn any bridges. (Yes, Yuri, I'm a wimp.)

There will be very few more cold days here to check it after tomorrow. The coldest average low temp here is 32 degrees, average high 53. This problem happens even when it's slightly above freezing outside. But who knows...
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Old 01-31-2014, 07:59 AM   #42
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Natural gas furnace combustion air intake question.


I suspected he would. Try my tee method as it is based on real world experiences. I have never seen any furnaces over 70 or 80,000 BTUs (Lennox 70, Carrier 80) vented with 2" pipe so going to 3" may be the real solution.

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