I can hear liquid sloshing in the 5″ ABS exhaust vent from my high-efficiency propane furnace. I had the furnace and vent installed 9 years ago. The ABS exhaust and inlet lines are about 35′ long, with one right angle turn. The drop over most of the run appears to be about 1 foot. I am guessing that the ABS has sagged in the middle of the run and that condensation from the exhaust has pooled there.
Should I tap into the ABS to drain it or should I try to restore the slope and let the water drain back into the furnace? It sounds like there might be a couple of quarts of water in there.
–longwave
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That can be a very dangerous problem. If you get enough sag, you will eventually completely plug up your exhaust with water. Do you really have a 5" pipe??
You must be on the edge of having the exhaust flow sensing switch, shutting your furnace down. If that switch were to fail, you could have a carbon monoxide problem in your house.
That's one reason I don't like ABS for flue piping. It is not nearly as rigid as PVC. You are going to have to straighten out your piping and make sure it is sloping on a consistent grade with no pockets.
Yes, BoJangles, the exhaust pipe is ABS, but I was mistaken about the diameter. It is 3.5" O.D.
I realize that the build up of water in the exhaust is unsafe. What's the best way of getting rid of the build up before correcting the slope? Can I drill a hole into the bottom of the exisiting line and then plug it when the water drains? Alternatively, if I correct the slope with the water in place, is there a drain in the furnace that will divert the incoming water from the mechanical/electrical components.
--longwave
I DO NOT KNOW about you're particular furnace, but mine has a drain that runs to the floor drain in the basement, and it regularly makes water. The HVAC guy even warned me not to try to level the exhaust pipe where it comes through the basement wall, he said the furnace was designed to take in water in the event of rain or melting snow.Not much of an answer in your particular case, but there are furnaces out there, that it would be acceptable to simply straighten the exhaust, and have the water run into the furnace.Mine is a Coleman (York) 92+.A medium to large guy named Alan, not an ambiguous female....NOT that there is anything wrong with that.
You should check your installation manual for the furnace if you have one.
Generally, the exhaust pipe should slope back towards the furnace about 1/4" per foot. It sounds like you have plenty of grade, but your pipe is not straight.
You will always get condensation in the exhaust flue on a run as long as yours. Your furnace is designed to collect and drain that condensate.
You don't need to drill any holes in the pipe. You should just raise it slowly to the proper grade and let the water drain back out when the furnace is not running.
You just need to straighten the pipe to the proper grade with more hangers.
Thanks, BoJangles, for the clarification re: how to do the draining. It's taken me this long to find the time fix it. I found the drain for the vent pipe - in the housing for the vent exhaust blower. I raised the vent pipe where it was sagging and was relieved to hear the condensate flowing back towards the furnace and further relieved to find that the drain's outlet tubing was doing its job. The cause of the problem was skimping on the installating of the pipes. One extra pipe hanger would have prevented the sagging.
--longwave
Good for you!!
There is a drain in the furnace.
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
Sure, get some ABS cement and cut the line at the lowest point, install a threaded drain at that point and your done. Might also be wise to place some supports in that length of pipe.Plumbing code says, I believe, that your not suppose to have any horizontal runs in vent pipe for furnace. Horizontal = anything less than 45 degrees from level(horizontal).
> Plumbing code says, I believe, that your not suppose to have any horizontal runs in vent pipe for furnace. Horizontal = anything less than 45 degrees from level(horizontal).I doubt that any plumbing code says that. Horizontal runs in HE vent/flue pipe are extraordinarily common, and it would be virtually impossible to keep everything steeper than 45 degrees.Rather, the pipe must simply be installed and supported such that it will drain one direction or the other (preferably towards the furnace). Generally about 1/8" to the foot should be sufficient.Installing a draincock is unnecessary and introduces an unnecessary (and therefore hazardous) joint in the pipe.
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
Please, if you don't know what a code says, don't reply.
Plumbing code has NOTHING to do with heating vents.
What is a threaded drain? Should he leave it open? You didn't say. Nothing like a little CO in the house.
Manufactures IOM state what grade and what material is to be used for venting.
One other reason not to tap & drain (besides the CO) is that if what is in the vent is exhaust condensate - as opposed to water - then it is acidic and will gradually eat certain types of piping. I know commercial high efficiency boilers incorporate a treatment section on the condensate drain to neutralize the acid before discharging into the plumbing system - I can't speak for a residential furnace, but I would be careful about what the furnace drains in to...
Now there's two pieces of bad advice if I ever heard it!!
Surely you can't be serious???
Sometimes I shoot from the hip without thinking and blow my foot off. I was mixing up gravity venting of combustion byproducts, that together with further mix ups of the plumbing code with mechanical code and I just got gibberish. Your comment about slowly raising the pipe to let the condensate drain back to the furnace was probably the best idea. That, together with fully supporting the vent pipe would solve the problem in the original post.
We all have our moments! ;)
You should restore the correct grade to the pipe. I worked on a house once that had two furnaces each vented thru PVC pipe and one day I noticed the pipes gurgling and spitting out water. Checking under the house I could see that the installers had barely used pipe hangers, just run the pipe with long spans and it had sagged, so water was collecting in the middle. In that case the grade was down to the exterior, but you may have a different situation. Sounds like you need to check how much grade is available, possibly relocate the exit fitting higher or lower, and add some pipe hangers. You can probably use plumbers tape safely, but I vastly prefer "zip stick" hangers.
If there is any question about doing this correctly yourself, get a good HVAC shop to come out and do it.
I did not realize that ABS was every used for furnace exhaust. All I have heard of is PVC.
But I don't really have any specific knowledge in this area.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Here's what a zip stick looks like. Because your sagging pipe has probably developed some "memory", I would use these along the entire run, so that when you pick up the sagging middle it doesn't just raise the ends accordingly.
http://www.plumbingsupply.com/pipehangers.html
Heh, I like those hangers. I've never seen them before.
The version I have come with two little nails stuck in the end, so all you need is a hammer and a saw to cut them with. Then, git in that crawl space!
If the pipe has sagged, tie it up (eg, with pipe hanger strap) so that it's straight and with at least a slight slope to one direction or the other. There should be no low spots where condensation can collect.
Do not "tap" it.
Are you sure it is ABS?
The was a plastic, HTPV, aka "Plexvent ," "Plexvent II" or "Ultravent" used early for flues on 90+ high efficiency which is usually gray or black which was recalled: http://www.cpsc.gov/CPSCPUB/PREREL/PRHTML98/98072.html
(Some internet sites talk about "black plastic" being recalled, but I'm pretty sure they aren't aware of ABS and think all black plastic is HTPV)
There are still some systems out there with it.
I believe it is critical to be sure (i) any HTPV is replaced and (ii) there is no sag in the flue (as discussed here) and the furnace is regularly serviced by a qualified HVAC tech who uses a combustion analyzer to tune it. (Sorry, but a "blue flame" isn't necessarily a good flame when you actuly measure CO, CO2 and 02 in the flue gasses)
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
How do you tune a 90% that has a disturbed flame, the flame temp changes from day to day, and so does the load?
(just having fun, but it's also a serious question. The good doctor never did answer the same question.)
Edited 2/24/2007 12:33 pm ET by rich1