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
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.
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.
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
I have a CO detector in the furnace room just in case.
Google sucks for Usenet access. Get yourself an offline reader and a
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
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
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.
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.
I agree that we should know what we're talking about before we
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
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.
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
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
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.
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.
The fan I have is similiar to this:
And here are pictures of my water heater
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.
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.
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
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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