This is very strange. I’ve recently posted a question here about condensation in the 30′ long ABS EXHAUST vent from my propane furnace. I got some good advice: correct the slope of the pipe and let the condensed water run back to the furnace and out the drain in the bottom of the housing of the exhaust blower. Now I find that there is also liquid in the air INTAKE pipe – also 30′ long, 3″ ABS. It’s probably been there for a while; I just didn’t notice it. If I correct the slope on this pipe the water will run into the furnace and presumably into the housing where the burner is located. That can’t be right. I propose to cut a small hole in the low spot of the existing run and let the water drain out before correcting the slope of the pipe. Then I’ll plug the hole. This should be okay for an intake pipe, right?
Can anyone suggest where the water is coming from? The configuration of the intake and exhaust pipes where they exit the house looks like what’s in the furnace installation manual; there is a 90-degree elbow in the intake pipe and it is facing downward, about 30″ above the ground. There are no sprinklers in that area. I live in eastern Ontario. We have very cold winters and hot humid summers.
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How much water?
How much water? I would guess there's at least a quart of water in the pipe, judging by the sloshing I hear when I jostle the pipe up and down.
--longwave
Seems odd. Is the pipe in an unheated crawl? If in heated space cold air from outside wouldn't cause any condensation in the pipe, and any water that did get in should evaporate after a couple of days of operation. Even in an unheated crawl there shouldn't be any significant condensation, though it might take a hair longer for water that somehow got in there to evaporate.I'd suggest you check the connections at the furnace to be sure they're tight, with no leaks. Is there adequate separation between the exterior intake and exhaust ports?
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Condensation is a possibility. If there is any recirculation of the flue gases, there will be lots of water.
Edited 3/8/2007 10:15 pm ET by rich1
There shouldn't be significant recirculation, and there's no other reason for condensation to occur. Puzzling
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
No, but his pipes should have been hung and graded properly to begin with.
This is true. But this sort of problem is depressingly common.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
And it still doesn't explain how the water got there.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"And it still doesn't explain how the water got there."
Any chance there's a problem with the furnace's drainage/installation so that the condensate in the furnace is backing up into the flue/intake? Remote, but possible, I suppose.
Mike HennessyPittsburgh, PA
It would be wise to compare the instructions in the installation manual with what was actually done, given that we already know the installer was a jackleg. If the OP doesn't have an installation manual it should be possible to download over the internet, or, as a last resort, order one from the mfg.There are various adjustments that need to be made in a condensing furnace, depending on whether it's installed vertically, horizontally, upside-down, etc. (One reason that the industry likes condensing furnaces is that a single furnace can be installed in many different orientations, whereas for conventional furnaces a different design is required for each orientation.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
There's no way for the condensate to back-up into the incoming pipe. Both the intake and exhaust pipes are steeply sloped where they enter the furnace room. It's the long runs from there, across the basement to the out-of-doors where they are virtually level (and sagging). The more I think about it, the more I think it's a one-time problem. There's no way it could be condensation.
The pipe runs through my heated basement directly to the outside, where it makes a 90 down turn. There is about 20" between the inlet and the furnace exhaust above it. I agree that it could hardly be condensation in the pipe. I'm now assuming that it was a one-time occurance (freak weather, falling snow getting sucked into the pipe, kids?)
The connections to the furnace all seem tight. There are a couple of spots on some of the joints where the ABS cement hasn't oozed out between the fittings.
Would it be okay to drill a small (1/4") hole in the middle of the low part of the pipe and then plug it with silicone after the water drained out?
Should there be a screen over the outside inlet to keep wasps and mice from nesting in the pipe during the summer (when the furnace is never one)?
--longwave
Re the screen, read the instruction/maintenance manual -- I think most advise against it, or have important restrictions. Any restriction on airflow can cause the furnace to fail to start, with resulting frustration.To get the water out, I'd advise getting a Fernco of the appropriate size, if possible a "repair" version without the center ridge. Remove the rubber gasket from the sleeve, split it lengthwise, and, if not a repair version, carve out the center ridge with a razor blade or some such. You may also have to do some surgery on the metal band to allow it to separate fully.After drilling the hole and draining, wrap the Fernco around the pipe, with the slit opposite the hole in the pipe.You can also make a "poor man's Fernco" with a sheet of rubber, a square of sheet metal, and a couple of worm clamps. The rubber only needs to be 2-3 inches square.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Thanks, DanH. You're repair suggestion makes more sense than my idea of using silicone to seal the hole.
The installation manual says that "consideration must be given to the blocking effect of louvers, grilles and screens" and indicates that quarter-inch (or larger) screens would have zero blocking effect, so I think I'll try that once I get the water out.
--longwave
I just noticed this thread and I do have another idea for you. I can't imagine how you got water in the air intake piping, but lets say it was a rare happening where some snow may have gotten blown in there.
I would go outside and cut the 90 degree elbow off of the intake pipe. It may not even be glued, so check that first.
Make sure your furnace is shut down and then take a shop vac ( and some type of hose extension) and just suck the water out of the pipe from the outside.
There are a number of ways to extend the hose. You can tape it to a section of 2" plastic pipe or tape it to some type of flex hose from the hardware store or simply buy a regular vacuum hose extension. Just slide it down the pipe to where the water is and suck it out.
Go get yourself another 90 degree elbow and attach it to the 3" abs without cementing it in case this happens again.
Thank you, BoJangles. Sucking the water out of the pipe from out-of-doors seems like the first choice, if I can reach get to it with the shop-vac hose. You've provided a couple or reasonable approaches.
--longwave
I would think that, even without removing the elbow, you could slip some flexible plastic hose (maybe 1/2" OD) through. Weigh the end down somehow, and measure out enough to reach the center of the dip. Cobble an adapter to the vac hose with duct tape or whatever.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
>>Would it be okay to drill a small (1/4") hole in the middle of the low part of the pipe and then plug it with silicone after the water drained out?Don't even worry about plugging it - it's combustion air - a 1/4" hole won't make any difference.
With my mouth I will give great thanks to the Lord; I will praise Him in the midst of the throng. For He stands at the right hand of the needy, to save them from those who would condemn them to death.
- Psalms 109:30-31
It is possible that your furnace is pulling in enough exhaust air for combustion to cause your problem.
You mentioned that the exit termination looks like the installation manual, but have you measured the installed distance between intake and exhaust and then compared that to the instructions? Is your vent system the correct size? Bigger is not better. Most installations less than 60' (including elbows, each run- not added together) on furnaces 80k BTU and less can usually be installed with two inch pipe. Installation manuals are very specific with venting instructions.
If the intake is too far away from the exhaust, then it becomes easier to pull exhaust air back into the unit. Dead corners and driving wind/rain/snow can help the problem.
The exhaust contains a great deal of humidity. It will not take much recycling to create the small pool of water you are describing. If it is cold enough, the water vapor in the exhaust will freeze almost instantly and become much easier to pull in those little lightweight ice crystals.
Blowing fine snow will cause the same thing- especially if the vent terminations are on the predominant wind side of your home. Then the ice thaws in your home.
Three inch exhaust pipe slows the exhaust stream down considerably. One solution is to put a 3 x 2 coupling reducer at the end, which speeds up the exhaust stream. This gets the humid exhaust further away from the intake. Some manufacturers have this detailed in the instructions. It works.
Premade stainless steel 1/2" mesh screens are available for your vent terminations- they press fit into the hub end of a fitting. Usually, one will come with the furnace (not the cheap cheap builders models). PVC screens are available for 3" pipe. Some areas here require screens by code.
Do not waste your time with galvanized hardware cloth. It will rot away quickly on the exhaust and the intake will rust where you cut it.
A word of warning on the screens... The exhaust pipe will never freeze shut in a proper installation. However, the cold screen makes a nice place for humid exhaust air to condense out and freeze on the intake pipe. Seen it happen, and it makes for a nice expensive service call. Given the right weather conditions, intake pipes can freeze shut without a screen.
A cleanout tee and threaded plug, installed near the furnace on the intake pipe, will allow the furnace to operate using indoor air for combustion in an emergency. The frozen intake pipe can then be thawed out at a more convenient time. An extra $5 in parts.
Edited 3/11/2007 9:07 am ET by danski0224
Thanks for your analysis,danskj0224. Your suggestion that the exhaust gas may be recycling suggests the cause of the problem to me. On very cold days (below 0 degrees F)I have noticed icicles hanging down from the exhaust elbow - created from the condensed combustion gasses and perhaps as much as 6" long. I'm guessing that when condensate drips from these icicles it falls a short distance and is sucked into the incoming air pipe.
I will test my hypothesis with an eye dropper tomorrow.
Thanks again,
--longwave
(The furnace manual calls for 2" piping for 100,000BTU or less, and 3" piping for 120,000 BTU or more. My furnace is 120.000 BTU so the 3: pipe should be okay. I have 3 elbows in each run, in addition to the outdoor terminating elbows. The pipes exit side-by-side in the middle of a long straight wall: no pockets of dead air. In operation, I observe the exhaust gas pluming high and away in the breeze, well away from the downward pointing inlet.)