Wierd problem with draft vent of water heater.

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I have a 6 month old Sears (AO Smith) 50 Gal gas water heater. While in my basement the other day, I noticed the plastic red " HOT" and blue "COLD" rings around the heat trap nipples were melted around the area where the exhaust flue pipe is. So I raised the T-stat to fire up the water heater to test, but found no excessive heat around the exhaust and draft hood. Testing with a match confirmed the draft was good. By the way, the exhaust pipe is 3" rigid duct. The specs to the water heater allows 3" or 4" ducting. I took apart the duct to check for blockage, and it looked clear. Now last night I was in my basement again, and this time I noticed excessive heat around the draft hood, So much that I could not keep my hand there for that long. When I did the draft test with a match, the flame was blown out. I turned off the water heater and tested again with the match, and the flame was still blown out. I also tested it with my furnace vent without the furnace running, and that was blown out too. The only thing I can think of is that it was very humid outside last night and the air was still, possibly causing no updraft. I rechecked about an hour later, and the draft was good. What could cause this?
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Fight with an old wood stove for a few years to learn about how well [or not] things draw.
If a woodstove was having trouble drawing on certain days, it was almost always on low pressure days. Sometimes the fix was as easy as making the chimney taller. Above the peak of the rook is good if you can do it.
If a breeze from a certain direction is causing your problems, you can get a cap that rotates like a weathervane to supposedly optimize draft. [never used one- but I've seen them in use]
Be sure your CO & explosive gas detector is working properly. You've got a potentially deadly problem there.
Jim
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wrote:

Also check for exhaust fans in kitchen and/or bathroom that may be working and/or a dryer may also be adding to negative pressure in the house. Any one of these things coupled with heavy humid air reducing draft or multiple equipment may create the negative pressure. You need to experiment to identify the cause. You may need to add some "make-up" air supply to the area of the furnace/water heater to replace the air being removed.
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-snip-

Good points-- I hadn't thought about negative pressure. If the OP has central A/c it could very well be causing some negative pressure there. And it would be worse on hot/humid days.
Jim
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wrote:

The above are all good points. You have a potentially deadly situation that needs sorting out.
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Sorry for posting late, but for some reason, I saw no new posts for about a week on this group.
Anyway,I found my problem. It was my attic fan. Hard to believe since I live in a split and the attic fan is 2 stroies upon the other side of the house with adequate ventilation from the roof vents. I don't know if getting a slower motor would help, but the motor I have on there now is 4 amps.
I do have central air, but when I shut it off, the draft on the water heater was still no good. Thats what made me think about the attic fan. I have a CO detector in the furnace room just in case.
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free server- You'll thank yourself.

That's step one-- you've located the culprit and it is negative pressure. For the summer, a cracked window in the basement should cure it. I might consider a backwards dryer vent [something a little more elegant is likely out there] to keep that pressure from going negative.

If you have a good digital one it will tell you what the highest level of CO has been. I'd check it weekly for a while to see if it has been spiking just under the set-off level. Because CO is a cumulative poison, you want to keep close track of it over the long haul.
Jim
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On Wed, 10 Aug 2011 03:30:15 -0700 (PDT), Mikepier

Sounds as if you have an opening to the vent from the attic which allows the positive attic pressure with the fan on to flow air down the WH vent. Check if the vent goes thru the roof and is not obstructed or possibly it has a disrupted joint. If not, check for a second appliance in the attic with the vents combined. If a combined vent exists, the water heater vent should be routed thru the attic and to the open air. CO is a definite danger in this installation the way it is.
--
Mr.E

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The water heater is vented through an exterior brick chimney. The attic fan is on the opposite side of the house.
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Mikepier wrote the following:

What kind of attic fan are you talking about? The kind that is installed in a gable end vent of the attic or in the roof, or a whole house fan that exhausts air from the living area into the attic? There is no way that a typical gable or roof attic fan can exhaust air from a room two stories down and on the opposite side of the house, unless you have no soffit vents in the attic, and even then, the attic door(s) would limit the suction from the rest of the house.
--

Bill
In Hamptonburgh, NY
  Click to see the full signature.
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I agree that we should know what we're talking about before we speculate.

My speculation previously was based on the attic fan ['whole house fan?'] in my house. It is a big bruiser right over the drop down staircase. The drop down staircase is near the top of the stairway to upstairs. If you open the door at the bottom of those stairs while the drop-down is down, it will blow your hat off.
My drop-down isn't real tight- and I crack it a bit in the summer to help cool the upstairs. [on the 2-3 days a year I use the AC I close it.]
If a house was buttoned up tight, and there was insufficient gable venting, [old houses rarely have enough] I can picture negative pressure in the basement.
I can't think of another reason the two would be connected- and the OP seems to have made the connection.
Hey Mike- got a barometer? I'm not sure it would work, but I'd have to do the experiment. I suppose a quicker [but not nearly as fun] way would be to see what happens when the fan is running, but a few windows are open so no negative pressure can build up.
Jim
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On Wed, 10 Aug 2011 09:05:28 -0700 (PDT), Mikepier

You just put that water heater in, right? Think you posted pictures and we were talking here about vent placement. Did the old heater have 4" vent pipe? How many inches did you stick in the chimney? Did you put in under the furnace vent instead of side by side or under? I think I said my 4" water heater vent was a few inches directly over the 8" furnace vent. I checked just now and that's how it is. Don't know if this means anything, but something to consider since as I recall you changed the setup.
--Vic
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I had an open "chimney from my basement thru two floors into the attic from a chase where all the plumbing ran from the basement to the upper floors. I could feel cold air coming into the basement in the wintertime. The solution was to put lots of insulation at the top of the "chimney" to stop the airflow. With an attic exhause fan in one gable end, I am sure that if the insulation had not been packed tightly at the top of the "chimney, I would have had negative pressure in the basement.
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The fan I have is similiar to this:
http://www.broan.com/display/router.asp?ProductID 0667
And here are pictures of my water heater
https://picasaweb.google.com/mikerock92/HwHeaterFinished?authuser=0&feat=directlink
I tried another test yesterday.WIth the attic fan on, I turned on my water heater and noticed the area around the flue was hetting hot. I opened a basement window, then the area was not hot anymore. I guess this reconfirms the fact there is negative pressure in my house.
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On Mon, 8 Aug 2011 03:49:41 -0700 (PDT), Mikepier

Somethiung nesting in your chimney???
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Mikepier wrote the following:

If it's any comfort to you, I have a 5 year old GE propane water heater, and the red and blue plastic surrounds of the hot and cold pipes are warped from heat. I also have black foam pipe insulation around the hot pipe to reduce heat loss until it leaves the basement. It too, is slightly melted at the bottom. Maybe it's due to blow-by during windy conditions when the heater is heating the water. I'm not going to worry about it unless water starts squirting from the heater around the pipes. My office and shop are here in the basement, so I'll know when that happens. Maybe some metal sheeting on the sides of the flue next to the pipes will prevent further melting.
--

Bill
In Hamptonburgh, NY
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-snip-

Do you have a CO detector that remembers its highest reading? I wouldn't worry about fire or explosion so much-- but the poisoning from CO is accumulative, so a little bit over a long time will just knock you out at your desk [or over the table saw] some evening.
I'd be real curious if the CO is spiking when the heater isn't drafting right.
Jim
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On Mon, 08 Aug 2011 03:49:41 -0700, Mikepier wrote:

If you've confirmed the draft is good, don't worry about the rings.
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He obviously has confirmed that the draft is NOT good. At least not always, hence the problem. If it were good it would not blow out a match and the plastic would not be melted. I had melted insulation on the water pipes on mine and found out there was a mouse nest inside the vent pipe. I would get the whole path inspected, from the top of the chimney to the water heater.
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Do you have an exhaust fan? Attic or whole house fan drawing lots of air? They can cause back drafts if there is not enough window/door openings to allow lots of air in.
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