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?
-------------------------------------
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
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.
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
On Sep 6, 3:13 pm, michaelcherr_at_gmail_dot snipped-for-privacy@foo.com
(michaelcherr) wrote:
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.
michaelcherr had written this in response to
http://www.thestuccocompany.com/construction/Re-Water-Heater-s-vent-question-17980-.htm
:
michaelcherr wrote:
Thanks for catching my math error. I used diameter instead of radius.
(And I just tested into calculus at the locall community college)
I havent heard of totally sealed combustion for water heaters. I knew
that was available for furnaces. When mine dies, I will probably go with
that.
I had thought about the direct vent ones, but decided otherwise because of
price.
I will return the one I already bought and buy a direct vent one, or
sealed combustion if available.
Thanks for your helping me to get this done safe.
The direct vent ones are a bit more expensive, but thats far cheaper than
the cost of worrying about poisoning the occupants.
-------------------------------------
*I've noticed that in several towns in my area the building inspectors are
requiring that the original 3" vent installed by the builders be changed to
4" when the water heater gets replaced. It might have something to do with
the increase in BTU's, but I am not sure. You should check with your town
regarding your installation. As Bill mentioned fresh air is important for
combustion and draft. I am wondering if the top of the chimney became
clogged with a birds nest or other critter, would the exhaust from the lower
water heater come out into the upper apartment? I guess there is probably
some sort of back draft damper that can be installed.
michaelcherr had written this in response to
http://www.thestuccocompany.com/construction/Re-Water-Heater-s-vent-question-17982-.htm
:
In case anybody has a similar question, I found the answer to my original
question.
http://books.google.com/books?id=W3p0btt2GXEC&pg=PT122&lpg=PT122&dq=sizing+vent+for+multiple+appliances&source=bl&ots=oH5cddS5Uf&sig=S_gJOfKwLne6lUCo54o9SaVnsYs&hl=en&ei=-nakSpu_GJCLnQeL073SBA&sa=X&oi=book_result&ct=result&resnum=5#v=onepage&q=sizing&f úlse
In section 5.11 of the 2006 International Plumbing codes handbook, it says
that two appliances sharing a common ventalation system must be on the
same story, with an exception for engineered type systems.
I guess I will be going with electric, power vent and run PVC, or running
two flues inside the chimney.
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