I'm installing a 35'x5" round aluminum chimney liner because my exterior ch
imney (terracotta inside block) is showing wet spots in the mortar joints.
I have a 36,000 btu gas fired hot water heater that has a 3" gravity flue p
iped to my chimney and also a 100,000 btu input 80% power vented heater wit
h a 3" flue that bumps up to 5" before it enters my chimney. I'm a pipe fi
tter by trade so I deal with installing these all the time but never deal w
ith the flue side. My question is when I bring the 5" through my chimney an
d tie in a 5" wye, which appliance should go on the bull of the T? I've bee
n told both ways, just curious what some thoughts are. Thanks.
On 02/06/2014 05:04 PM, email@example.com wrote:
I just posted a few days back that I'm going to have to put a liner in.
My days of going up on the roof are over so I'm going to contract it out...
but I had given it some thought.
Since I have a gas furnace and a gas water heater, the only thing that
would fit inside my chimney would be a reducing "Y".
Maybe your chimney is larger than mine but I don't see that a "T" would
fit very well.
On Thursday, February 6, 2014 8:21:20 PM UTC-5, philo wrote:
I'm not qualified either, but the ones I've seen, when
you have a furnace and gas water heater feeding into a chimney,
the furnace has always been the direct route, with the WH
coming off the side from T or wye. Kind of makes sense that
you'd want the higher capacity appliance to have the direct,
straight path. That's how my old furnace was routed, but
it also had a larger vent from the furnace than from the
WH. Now furnace is gone and WH goes straight into a liner.
On Thursday, February 6, 2014 6:04:08 PM UTC-5, firstname.lastname@example.org wrote:
. I have a 36,000 btu gas fired hot water heater that has a 3" gravity flue
piped to my chimney and also a 100,000 btu input 80% power vented heater w
ith a 3" flue that bumps up to 5" before it enters my chimney. I'm a pipe
fitter by trade so I deal with installing these all the time but never deal
with the flue side. My question is when I bring the 5" through my chimney
and tie in a 5" wye, which appliance should go on the bull of the T? I've b
een told both ways, just curious what some thoughts are. Thanks.
I'm not an expert but I've owned homes with the gas hw heater and gas T'd t
ogether before myself. I've always wondered how the waste heat from the hw
was enough to get out the vent without condensing when the furnace was not
One consideration is that your next gas furnace will probably be a condensi
ng one. How old is your furnace and hw heater now?
It's interesting that you mentioned that...because that was the very
thing I did not bring up before. The building inspector I talked to told
me that the water heater alone is /not/ sufficient without the furnace
The reason I did not mention that was because it did not seem right...
but then realized that in the summer, when the furnace is not
running...since it's warmer, there of course would not be a condensation
problem. In my situation it needs to get to -10F before there's a problem.
On Saturday, February 8, 2014 9:44:11 AM UTC-5, philo wrote:
nts. I have a 36,000 btu gas fired hot water heater that has a 3" gravity f
lue piped to my chimney and also a 100,000 btu input 80% power vented heate
r with a 3" flue that bumps up to 5" before it enters my chimney. I'm a pi
pe fitter by trade so I deal with installing these all the time but never d
eal with the flue side. My question is when I bring the 5" through my chimn
ey and tie in a 5" wye, which appliance should go on the bull of the T? I'v
e been told both ways, just curious what some thoughts are. Thanks.
e hw was enough to get out the vent without condensing when the furnace was
That's the essence of the condensation issue. Condensation becomes
a problem when a chimney is sized for a furnace plus WH and then the
furnace is converted to direct vent. You then have a chimney that is
too large for just the water heater, making it very easy for condensation
to occur. With the large chimney and the furnace, when the weather was
cold enough for condensation to occur, the furnace was running enough
of the time to keep the chimney free of condensation. Also, with a
chimney that is too large, you won't get proper drafting. So, if you
go with a direct vent furnace and keep an existing WH,
you probably need a flue liner to reduce the
size. I guess at some point, if the run is long enough and the climate
cold enough, you're going to get condensation anyway, because the WH
doesn't generate enough heat. But with a liner, any condensation is
going to stay in the liner, not screw up the flue.
I don't think a normal furnace has enough exhaust heat to evaporate
condensation. I noticed a lo of water inside top of mine earlier in the
year. Even some moss. That's without liner.
On my living house, I got water heater up old chimney which is external.
HVAC installed it. It's probably ok except during a heavy storm, my
uncovered chimney leaked some water of of bottom clean out from old oil
burner furnace, which originally was coal.
My house originally was coal. When I bought it, it used an oil burner
which I replaced and went to gas. I installed it myself.
Eventually as I finally managed to start saving up some money I had
professionals put in a new one.
They made one small error. The exhaust pipe going into the chimney was
not cut and the lower portion jutted out and collected a small amount of
moisture when it rained. That was just enough to clog the air flow
sensor. Once I cut the pipe flush, I have had no more problems.
On Saturday, February 8, 2014 11:34:46 PM UTC-5, Gz wrote:
For the most part the furnace doesn't have to evaporate the
condensation, the exhaust gases just never condense to begin with.
A conventional furnace is only 80% efficient. If you have a 100K BTU
furnace, you're putting 20K BTU up the chimney. If the chimney is
properly sized, it will keep it hot enough when it's cold out so that condensation is minimal.
If you take the chimney that was sized for a 100K BTU furnace and a
35K BTU water heater, ie 135K total and remove the furnace, then you
have a problem. The chimney is now oversized and the WH is typically
going to run a lot less
and for shorter periods than the furnace did. When it's 20F outside,
with the chimney not in a heated space, then you will get condensation.
And over time, with a gas furnace, it will deteriorate the mortar in
the flue joints because of the acidity. You might not see any evidence
of problems for a long time, but when you do, it will be too late.
I noticed a lo of water inside top of mine earlier in the
I think not. Like 10x10 at least. I noticed the moisture when outside temps
were 40-50 degrees. This is one shaft. Might have been 4 shaft with two
chimneys. 1900 house. I have not run the water heater yet. Its been off for
going on 3 years. There is also a trail of minerals on the bottom of the
flew to the furnace. I even think the minerals got on the exhaust fan
blades. Fun times.
The two chimney bottoms are also part of the support structure. All other
shafts are top sealed off.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.