I have a 75 gal water heater with a 4 " vent going into a chimney. If I wanted to add a second water heater, what would be the proper way to vent both into the same pipe? Could I just add a Y and vent both through the same pipe going into the chimney?
Reason I wanted to add a second water heater is that this is a multi-family house and I wanted to split the demand for HW by zoning off the apts with 2 water heaters
By the way, my steam boiler vents into the chimney from the opposite side with its own separate vent pipe.
to add a second water heater, what would be the proper way to vent both
into the same pipe? Could I just add a Y and vent both through the same
pipe going into the chimney?
amily house and I wanted to split the demand for HW by zoning off the
apts with 2 water heaters
side with its own separate vent pipe.
A local tavern with 3 apartments upstairs just installed one of those
"instant" hot water heaters. There is no tank, just a flat box on the
wall operated by natural gas. It vents out a pvc pipe, and is supposed
to furnish unlimited hot water. I find this hard to believe, but it's
installed and the owner said it works great.
The tavern probably dont use much hot water, just enough to wash glasses
a few times a day, but 3 apartments on one heater is significant.
I'm not trying to sell you on this, just saying what I saw.
If you get the local code people involved, prepare to be forced to get a
permit, and they will likely want a second chimney, and in the end,
you'll spend a fortune. Or just install a Y and keep your mouth shut.
Gas water heaters dont really exhaust much of anything except getting
rid of some unused heat, and any carbon monoxide and other toxins from
the flame. But if you want to stay legal without a huge expense, the
high efficient unit with pvc venting may be the better alternative,
while you can keep those pesky building inspectors and costly permits
out of the picture. The less they know about you, the better!
Looking at our old furnace and Hot water tank set up 100K BTU furnace
and 20 some K BTU water tank were vented into on chimney. I don't think
those two water heaters will use as much as 100K BTU. But if the chimney
was originally sized for one tank, it becomes an issue. Now our chimney
is down sized with B vent insert to handle only water tank. Furnace is
upgraded to 98% Hi efficiency unit with PVC side vent.
Yes, this is done all the time where you have a gas fired heating boiler
and a separate gas fired hot water heater. In general, both will vent
up the same chimney.
I had a problem with having both a 640,000 input BTU boiler and a
251,000 input BTU hot water heater connected to the same chimney, but
the problem wasn't that they vented up the same chimney, it was that
they weren't connected to the chimney in the right order. Apparantly,
where I live, if there's a manifold chase feeding the chimney, the
smallest BTU appliance has to be connected closest to the chimney, and
the larger BTU appliances have to be connected progressively further
from the chimney.
In my case, I had two flues coming off my boiler, but the water heater
connected to the chase BETWEEN where the two flues connected to the
chase, so that was a problem. If you have two water heaters with the
same BTU output, I expect you can just connect them with a wye to the
Typically, any plumbing company that installs the water heater for you
will measure your chimney and determine if it's big enough. You can
find sizing tables online, like the ones on this web site:
'Chimney flue size rules: Flue diameter and height requirements for
Category I Draft Hood and Fan Assisted Appliances'
If it turns out your chimney isn't large enough, there are flue blowers
that can be installed that are basically flue fans that blow the flue
gas up the chimney rather than rely on natural convection.
On Sunday, September 8, 2013 6:15:20 AM UTC-4, CRNG wrote:
I'm not so sure about that. Appliance vents are sized and
governed by the number of BTUs. So, it depends on the
BTUs of those water heaters, what else, eg furnace is connected
to the chimney, size of the chimney, etc. Most likely, the
chimney has the extra capacity required. But I have doubts
about the 4" pipe from the water heaters, ie that you can
just put a "Y" in and the same 4" size that each had alone
is then OK for both.
Generally that 4" is just used for one. I've never seen
it connected to another water heater like that. I have
seen a water heater join a furnace vent before going into the
chimney, but in those cases the vent size joined is much
So, I would say:
If both WH's go into the chimney separately, you're OK provided
the chimney is sized to handle the max btus. If they get
combined into one pipe before going into the chimney, I would
check to make sure that pipe is of correct size.
Yes, it couldn't be a 4X4X4 wye, it'd have to be a 4X4X6 inch wye
connected to a 6 inch flue connector so the flue connector could handle
all of the flue gas going through it when both water heaters are firing.
Yes, but now you are grasping at straws. What will you think of next
to try to salvage you argument: the difference in smoothness of the
inside of the various pipes?
Or you just accept the fact that a 6" diameter pipe offers the same
cross sectional air flow resistance as two 4" diameter pipes of the
same length; and it didn't occur to you to check that.
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
I'm certainly no expert on chimney drafting, but for different chimney
heights, there are maximum horizontal distances that appliances can be
away from the chimney. The taller the chimney, the greater the
horizontal distance the appliance can be from the chimney. As long as
no appliance exceeds that maximum distance from the chimney based on
it's height, the appliance should draft up the chimney OK.
That might be the reason why you often see really tall chimneys rising
10 to 12 feet above the roofs of houses. Perhaps they needed that
height because the heating boiler is located on the opposite side of the
house's basement from the chimney. I always wondered why any builder
would extend the chimney so far above the roof line, and that's one
Often two appliances drafting up the same chimney at the same time will
work better than only a single appliance because the increased amount of
flue gas warms the chimney up more, and the result is better drafting
from natural convection.
When I used to help install furnaces. If we would put
in a PVC vent furnace, often we'd have to put in a
chimney liner for the water heater. Boss would
explain to me that there wasn't enough heat to keep
the chimney warm. The flue liner would be expanding
aluminum tube that went to the top of the chimney.
I'm not sure what the formula for that is.
Christopher A. Young
Learn about Jesus
On 9/9/2013 3:01 AM, nestork wrote:
On Mon, 09 Sep 2013 07:35:12 -0400, Stormin Mormon
YEs, and there is a difference between interior and exterior walls.
Some time back, we switched our boiler from oil to gas, they said our
chimney was fine because it was on the interior of the house. Had it
been on an exterior wall, it would have required a liner.
The water heater does however. The problem is that if the flue is too
large in diameter for only the WH it may not draft properly. And yes,
one would think that that would be a problem in summer.
I'm guessing stuff may have been done in the past that wouldn't pass
muster today. I suspect that a gas WH would require a separate flue
today and wouldn't be able to share the flue with the furnace as was
sometimes done in the past. I am not familiar with that specific area
of building codes however, this is just speculation.
replace "roosters" with "cox" to reply.
On Monday, September 9, 2013 2:53:26 PM UTC-4, jamesgang wrote:
The issue is condensation. In the winter, the chimney without
a furnace, gets cold. The gases from the water heater can
condense and the condensate is acidic. Over time, it can
eat away at the mortar, causing the chimney to fail. That's
also why it matter if the chimney is outside the heated
structure or inside.
If the home has a 90+ furnace with a abandoned furnace chimney then its probably better to install a stainless liner in the unused furnce chimney flue and connect it to the 2nd heater.....
since both chimneys are in use then get a power vent water heater for the 2nd water heater. they can vent thru the wall
You may also want to try posting this question on the
in particular, on their forum called "The Main Wall" at
You could post your question there anyway, but the fact that you have steam
heat also helps since they specialize in steam heat information and
I posted there about chimney issues and codes in the past and got great
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