I was under the house over the weekend removing “all wood and cellulose debris large enough to rake” and independently confirming or refuting structural work that the pest inspector says needs to be done, when I came to an area where the ground was damp. “Odd,” says I, “we already repaired the toilet sweep, and besides, that’s all the way over there. Is the tub leaking now?” Well, no, the tub lines are all dry, and so is the surrounding wood. But the sheathing is definitely damp a few feet over, where there is a penetration in the cripple wall for the shared vent for the water heater and an inoperative floor furnace.
Background: The house has three floor furnaces, all of them currently shut off (gas valve completely closed). The water heater vent pipe (after rising and then falling about 3″ over a 15′ run) tees into the vent pipe for one of them, then runs another 12′ horizontally before penetrating to the outside, to an old Paten (Patten?) flue — rectangular metal segments lined with, as I understand it, terra cotta. The flue is broken about 2/3 of the way up the side of the building, with one segment offset about 3″ from the one below it. I doubt the flue has a cap at the top, but I don’t know for sure. The masonry fireplace chimney doesn’t.
There’s no other source of water I can find. I suspect water has been entering the flue in the rainy season, either through the break in the flue or through an uncapped termination, and collecting at the bottom, slowly dispersing through the sheathing of the cripple wall year-round.
Yikes! How can the water heater possibly be drafting, with water in the flue? Let alone with the retrograde vent pipe and excessive horizontal run?
Glad I’m getting this fixed when I get my new heating system!!!
Replies
Greetings Rebeccah,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someones attention that can help you with advice.
Cheers
sleeps till noon but before it's dark...
I'm not an expert on this, but I'll see your yikes and raise you a double yikes yet. then those who know more can correct me or add to it...
#1 fact you should be aware of is that any combustion device will product warter vapour as a by-product of combustion.
#2 is that two such devices should never share the same vent
#3 is that nearly thirty feet of horizontal run is my biggest concern. There are formulas for calculating the allowable run in relation to the appliance and to the height of the stack. generally, I would not ever want more than a 115' horizontal run and that only when the verticle is over 20'
#4 you don't metion what kind of pipe this is, but is soulds very poorly designed and installed so it would not suprise me to see that it is also the wrong material. It should be double walled class B pipe, screwed together at every joint with a minimum of three screws and supported permanently at each such joint. The vertacle joints don't all need support, but do need screws or they can comeapart, as you have discovered.
summation - you are in extreme danger of potentially having a toxic buildup of CO gas exhausting into your house. The condensation orrainleak is merely an inconvenience by comparison, and has done you a favor by atracting your attention so you can have a qualified person make a more appropriate install.
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I'm not an expert on this, but I'll see your yikes and raise you a double yikes yet. then those who know more can correct me or add to it...
#1 fact you should be aware of is that any combustion device will product warter vapour as a by-product of combustion.
D'oh! Thanks for reminding me. I'd completely overlooked condensation as a source for the water. It makes much more sense than rainwater from last winter.
#2 is that two such devices should never share the same vent
The city of Oakland's building code apparently allows this under certain kinds of circumstances. A gas water heater and an 80% efficiency gas furnace are allowed to share a common vent and flue.
#3 is that nearly thirty feet of horizontal run is my biggest concern. There are formulas for calculating the allowable run in relation to the appliance and to the height of the stack. generally, I would not ever want more than a 115' horizontal run and that only when the verticle is over 20'
This one I've been learning about over the last year since I bought the house. First of all, there's a minimum slope of 1/4" per foot, but in addition there's supposed to be some sort of ratio like you say, between the horizontal run and the height of the stack. I don't know what the ratio is supposed to be. Once I get the new heating system done, the run should be about 10.5 feet, which is the distance from the water heater to the outside wall, or maybe 12' at the most if the water heater tees into the the furnace and not the other way around.
#4 you don't metion what kind of pipe this is, but is soulds very poorly designed and installed so it would not suprise me to see that it is also the wrong material. It should be double walled class B pipe, screwed together at every joint with a minimum of three screws and supported permanently at each such joint. The vertacle joints don't all need support, but do need screws or they can comeapart, as you have discovered.
No, it's not the right type of pipe at all. First of all, the vent pipe is single-walled. Second of all, it's 4" both before and after teeing into the floor furnace vent pipe, whereas it's supposed to be a larger diameter pipe after the junction of the two appliances. The flue is an old style, that I'm told is lined with terra cotta.
summation - you are in extreme danger of potentially having a toxic buildup of CO gas exhausting into your house.
No kidding!
I do have a CO detector plugged into the wall in the kitchen, which is almost directly above the water heater in the basement, and interestingly, it hasn't sounded off about anything. I'm guessing the only reason I haven't had any problem is because we don't really use that much hot water and the basement/crawl space is vented. We don't use the floor furnace AT ALL -- in fact, the gas to all three floor furnaces is shut off. I decided before I moved in that they were unsafe for a number of reasons.
The condensation orrainleak is merely an inconvenience by comparison, and has done you a favor by atracting your attention so you can have a qualified person make a more appropriate install.
Actually, I detected the moisture while *preparing* for repair work. I've already selected my heating contractor, but he has to wait until I get the termite work done, to decrease the risk of a sawzall attacking new flex duct. ;-) Hopefully, everything will be completed in the next two months.
good
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