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Posted by michaelcherr on September 6, 2009, 12:20 am
I currently have one (NG)water heater in the basement venting into an
unlined chimney.
I am adding a second one on the second floor for the hot water needs for
an upstairs apartment.
As I understand it the chimney is much to large for the single water
heater to be venting there.
I was planning on lining the chimney by running down sections of
galvanized pipe through the chimney from the roof, then capping off the
top of the chimney arouond the new vent.
In my mind I'm using the old chimney as a sort of pipe chase.
For the section with just one water heater, I'm assuming I just need 3",
what size should I increase it to after I tee in the second heater vent?
4" isn't quite double the area as 3", so would 5" be the correct size?
Is galvanized ok, or do I need stainless? Class B?
Besides powered vent water heaters, is there another option I should
consider?
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Posted by Bill on September 6, 2009, 10:45 am
This is important stuff!
The best source of information is the water heater manufacturer's
installation instructions.
In years past, there was a lot of waste heat going up the chimney and
"draft" was easy to obtain. Draft is heating of the walls of the chimney,
this causes heat to rise, and an upward draft in the chimney which then
carries the dangerous waste gases up and out of your home.
BUT these days they are making things like this energy efficient. This means
less heat goes out the chimney. Draft is harder to obtain. A smaller chimney
may be needed to obtain draft.
And of course an air vent to the outside so fresh air can enter the area of
the water heater. In order for air to flow out of the house, fresh air needs
to be able to flow in somewhere.
If the installation manual does not say you can install two water heaters on
the same chimney, I would call the manufacturer of both water heaters and
ask if this can safely be done and what size chimney.
The manufacturer's instructions may call for different size chimney pipe
depending on the specific model! (In the case of some new super efficient
furnaces, small PVC pipe is actually used these days! Very little heat.)
Then another concern I would have is that cold air could come down the old
"large chimney" and cool the new metal chimney pipe inside. This could kill
any draft you are trying to obtain. You want the metal sides of the chimney
pipe to get warm/hot. So perhaps double walled insulated chimney pipe, or a
cap on the top to keep cold air out, or some sort of filling inside the
chimney?
Again the manufacturers of these products are the best source of proper
installation based on the specific model/heat output through the chimney,
height of chimney, etc.
"michaelcherr" wrote in message
>I currently have one (NG)water heater in the basement venting into an
> unlined chimney.
> I am adding a second one on the second floor for the hot water needs for
> an upstairs apartment.
> As I understand it the chimney is much to large for the single water
> heater to be venting there.
> I was planning on lining the chimney by running down sections of
> galvanized pipe through the chimney from the roof, then capping off the
> top of the chimney arouond the new vent.
> In my mind I'm using the old chimney as a sort of pipe chase.
> For the section with just one water heater, I'm assuming I just need 3",
> what size should I increase it to after I tee in the second heater vent?
> 4" isn't quite double the area as 3", so would 5" be the correct size?
> Is galvanized ok, or do I need stainless? Class B?
> Besides powered vent water heaters, is there another option I should
> consider?
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Posted by Steve Barker on September 6, 2009, 11:47 am
michaelcherr wrote:
> I currently have one (NG)water heater in the basement venting into an
> unlined chimney.
> I am adding a second one on the second floor for the hot water needs for
> an upstairs apartment.
>
> As I understand it the chimney is much to large for the single water
> heater to be venting there.
>
> I was planning on lining the chimney by running down sections of
> galvanized pipe through the chimney from the roof, then capping off the
> top of the chimney arouond the new vent.
> In my mind I'm using the old chimney as a sort of pipe chase.
>
> For the section with just one water heater, I'm assuming I just need 3",
> what size should I increase it to after I tee in the second heater vent?
> 4" isn't quite double the area as 3", so would 5" be the correct size?
>
> Is galvanized ok, or do I need stainless? Class B?
> Besides powered vent water heaters, is there another option I should
> consider?
>
>
>
> -------------------------------------
>
>
>
you should have a qualified HVAC man put in a proper liner. They make
such products for just such an application. They are made of aluminum
or stainless.
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Posted by michaelcherr on September 6, 2009, 6:13 pm
michaelcherr had written this in response to
http://www.thestuccocompany.com/construction/Re-Water-Heater-s-vent-question-17979-.htm
:
The General Handyman unlicensed types are the only ones I could afford
right now, and I know more than most of them, so I'm going to do it myself.
I'm unemployed and have plenty of time to do research and do a
professional quality/safe job.
I am worried about the safetey of the existing setup, which is why I'm
asking questions and wanting to do it up right.
(I'm also probably loosing the grandfather clause because of me adding the
second)
I was planning on capping the chimney with masonry around the new vent to
stop drafts. Will that be enough. Going with double wall the whole way
seems overkill, but if it's needed, then I can do it. opinions?
The owner's manual shows illustrations where more than one appliance share
a vent, so I know at least teh one i'm adding allows it. I will consult
the other manufacture.
I am wondering how a professional HVAC person determines the correct size
for a vent?
I am familiar with/and can find charts and tables for every other trade it
seems.
My intuition tells me that since both appliances need a 3" flue which is
approx 28.27 sq in then I need a 5" flue after they join which is approx
78.53 sq in.
The rule I found was that for venting into a chimney the area can't exceed
seven times the flue size feeding it.
Since 78 is less than seven times greater than 28, then I should be fine?
I was thinking about going with stainless class B for the last section
exposed to the elements. I've seen way too many rusty galvanized ones.
Normally I see galvanized used for inside the house, but Steve suggested
aluminum or stainless.
Just guessing, but I don't think I will like the price of stainless.
Which would be better for inside the chimney: Aluminum or Galvanized?
Thanks for the time and advise
Mike
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Posted by Andy Energy on September 8, 2009, 12:04 am
On Sep 6, 3:13=A0pm, michaelcherr_at_gmail_dot_...@foo.com
(michaelcherr) wrote:
> michaelcherr had written this in response tohttp://www.thestuccocompany.c=
om/construction/Re-Water-Heater-s-vent-q...
> =A0:
> The General Handyman unlicensed types are the only ones I could afford
> right now, and I know more than most of them, so I'm going to do it mysel=
f.
> I'm unemployed and have plenty of time to do research and do a
> professional quality/safe job.
> I am worried about the safetey of the existing setup, which is why I'm
> asking questions and wanting to do it up right.
> (I'm also probably loosing the grandfather clause because of me adding th=
e
> second)
> I was planning on capping the chimney with masonry around the new vent to
> stop drafts. Will that be enough. =A0Going with double wall the whole way
> seems overkill, but if it's needed, then I can do it. =A0opinions?
> The owner's manual shows illustrations where more than one appliance shar=
e
> a vent, so I know at least teh one i'm adding allows it. =A0I will consul=
t
> the other manufacture.
> I am wondering how a professional HVAC person determines the correct size
> for a vent?
> I am familiar with/and can find charts and tables for every other trade i=
t
> seems.
> My intuition tells me that since both appliances need a 3" flue which is
> approx 28.27 sq in then I need a 5" flue after they join which is approx
> 78.53 sq in.
> The rule I found was that for venting into a chimney the area can't excee=
d
> seven times the flue size feeding it.
> Since 78 is less than seven times greater than 28, then I should be fine?
> I was thinking about going with stainless class B for the last section
> exposed to the elements. =A0I've seen way too many rusty galvanized ones.
> Normally I see galvanized used for inside the house, but Steve suggested
> aluminum or stainless.
> Just guessing, but I don't think I will like the price of stainless.
> Which would be better for inside the chimney: Aluminum or Galvanized?
> Thanks for the time and advise
> Mike
I think you should redo you math, a 3" diameter circle has less area
than a 3" square and a 3" square has on 9 sq in of area.
Your building department or a good venting book should tell you the
size needed. Try NFPA-54 2006 Edition (National Fuel Gas Code).
there may be a new addition out there. There is a standard on sq in
cross section of vent per 1,000 inbtu btu of the unit. Remember the
manufactures instructions or building department may over rule the
manufactures instructions.
As for hiring a qualified technician, good luck. I do whole hose
performance and test for Worst Case Depressurization and combustion
analysis (BPI) and about 40% of the contractor installed units fail
worst case, spillige or draft. Unless you can or who you hire can do
these tests do nto touch it.
My advice is to install a sealed combustion unit in both the upper and
lower or one to service both and forget the natural draft unit.
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> unlined chimney.
> I am adding a second one on the second floor for the hot water needs for
> an upstairs apartment.
> As I understand it the chimney is much to large for the single water
> heater to be venting there.
> I was planning on lining the chimney by running down sections of
> galvanized pipe through the chimney from the roof, then capping off the
> top of the chimney arouond the new vent.
> In my mind I'm using the old chimney as a sort of pipe chase.
> For the section with just one water heater, I'm assuming I just need 3",
> what size should I increase it to after I tee in the second heater vent?
> 4" isn't quite double the area as 3", so would 5" be the correct size?
> Is galvanized ok, or do I need stainless? Class B?
> Besides powered vent water heaters, is there another option I should
> consider?