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Old 03-22-2008, 11:17 AM   #1
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Furnace troubles, where's the water coming from...


About a week ago I noticed that the ignition was not firing every time when the t-stat was demanding for heat. The exhaust blower starts, but the sparker does not fire.

I found that there was a lot of water in the condensation traps, so I drained them and the furnace seemed to operate fine. That is until the condensation traps fill back up with water. I have drained the traps 70 or 80 times over the last week. I do not understand where the water is coming from. My intake and exhaust vents are clear, they was covered in snow a few times this winter.

The trap at the bottom of the burner box is collecting the most water so I assume that the water is coming in the intake and running down through the heat exchanger.

Is there anything I can do before my furnace destroys itself?

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Old 03-22-2008, 12:38 PM   #2
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Furnace troubles, where's the water coming from...


The water in a high efficiency furnace is created when the cold outdoor air (intake) is heated within the furnace itself. It is not unusual for a high efficiency furnace to create water during the winter months - thats why they have drains on them. What is unusual is that this water is causing your problems with your furnace operation. All the water is usually gravity drained in the system - check to ensure there is no blockage in the drain pipe and that all lines will allow flow to the floor drain. There should be an error code on your furnace explaining why it failed to heat....probable causes of the problem will be the pressure switch open. I have seen many units fail in winter even though they were installed "by the book" . I usually install them using a "one pipe system" - that being only 1 exhaust pipe vented outside and the intake drawing from the furnace room that has a combustion air intake into it. It causes alot less issues with pressure switch problems, the air being heated is warmer and therefore saves more money and the furnace will not create as much moisture. Let me know what you find. Hope this helps.

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Old 03-22-2008, 12:58 PM   #3
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Furnace troubles, where's the water coming from...


You have to heat combustion air one way or the other. Is there any prove that your way is better?
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Old 03-22-2008, 03:11 PM   #4
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Furnace troubles, where's the water coming from...


Gena,

well.....minus 10 degree air being heated up by your furnace......or that same minus 10 degree air being slightly drawn into a room that is 65 - 70 degrees and mixing with it before being drawn into the furnace....doesnt exactly take a rocket scientist to figure it out, but by all means call one if you want a mathematical formula to "prove it". Or try listening to someone who deals with high efficiency furnaces on a daily basis.
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Old 03-22-2008, 06:01 PM   #5
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Furnace troubles, where's the water coming from...


Well, it would be very strange to call to myself.
I donít know if itís a rocket science to figure it out or not, and I definitely donít remember a formula itís been already 22 years since I saw this formula last time, but as I remember that it takes the same amount of energy to heat the same amount of air for one degree no matter what. And if you bring that cold air in the basement you make basement colder in a first place. It why, in my opinion maybe Iím wrong, someone invented those intake and exhaust pipes.
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Old 03-22-2008, 07:41 PM   #6
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Furnace troubles, where's the water coming from...


Which just goes to show you that you havent worked on a high efficiency furnace or you would know what I mean. Sucking in 100% outdoor air and heating it is definitely harder on a furnace and your gas bill than it is to allow the furnace to draw air from a warm room with a atmospheric vent to the outdoors. Even up here in Canada at minus 40, I can stand beside the combustion air inlet and feel very little difference in room temperature. Now add to the mix the fact that over 90% over the trouble calls I get on high efficiency furnaces are due to pressure switch problems in cold weather (reallly reallly realllly cold air doesnt want to move down a small 2" pipe all that well) and the fact that most of the manufacturers of these furnaces allow for either a one or two pipe system installation makes it a no brainer. Simply put....easy elimination of the intake pipe ( provided you have a properly sized combustion air inlet and termination) will eliminate a great deal of the pressure switch problems that occur in these furnaces as well as reduce gas usage and increase the life of the heat exchanger. Class dismissed...or I'm putting you on call for the next cold snap we have. lol.
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Old 03-22-2008, 07:58 PM   #7
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Furnace troubles, where's the water coming from...


Gena,
Most manufacturers recommend using a 2 pipe system as preferred method of install. Intake pipe is to bring in a precise amount of combustion air into the burner box for complete combustion. cold or warm air has nothing to do with it. Depnding on application, where the furnace is located ie basement, closet, utility room, conditions of location and type of gas determines if can get away with one pipe or not. Although, I don't work in Canada in neg. 40 degree weather.

As for your problem, make sure your trap is clean, statman is right about something is plugged up somewhere. Usually, your trap is plugged up not allowing the water to drain.

Last edited by sgthvac; 03-22-2008 at 08:00 PM.
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Old 03-23-2008, 07:48 AM   #8
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Furnace troubles, where's the water coming from...


This furnace is a high efficiency "condensing" furnace which means the flue gases are ran through a secondary heat exchanger (similar to a car radiator) to lower the flue gas temperature. The flue gases contain the products of combustion which are predominately co2 and h20 in their gas like state. Cooling the flue gases before they exit the home increases the efficiency (compare flue gas temperature to a mid efficiency appliance) but the byproduct of this cooling is h2o in its liquid form (water). The water from your furnace is this condensate and it runs to a "p-trap". This "p-trap" is supposed to get full because it prevents poisonous gases from entering the home via the condensate line. So, don't empty this out (you need it!) check for blockage downstream of the p-trap. If the problem persists check with a qualified technician. The life of everyone in the home is depending on your wise decisions to save money. Fooling with the furnace may be pennywise but health/safety foolish.
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Old 03-23-2008, 03:12 PM   #9
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Furnace troubles, where's the water coming from...


Hey Guys

Thanks for the input. I found that the drain line had a low point in it where the water was backing up. Not enough to get up in to the pressure switch but it would have caused back pressure on the drain line I guess. Once I cleared the line and got a proper slope on the drain line the furnace seems to be operating fine.

As fare as the comment about exhaust gases coming through the drain line, my drain goes in to a tee, one end goes to drain the other is open. So is a p trap required here? Since my drain is clearly draining in to the atmosphere of my house.
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Old 03-23-2008, 04:19 PM   #10
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Furnace troubles, where's the water coming from...


You should already have a trap that comes with the furnace. What does the drain hoses on your furnace connect to? Most often they are tied to some configuration of a trap. You typiclly don't have to add one. Make sure it is clean.
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Old 03-23-2008, 07:40 PM   #11
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Furnace troubles, where's the water coming from...


OK that makes sense. Thanks, thing seem to be working fine today.

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