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Old 04-29-2013, 11:27 AM   #1
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Furnace/water heater vent pipe??


Not really sure if this should be here or in the plumbing section, so I'll start here....

House built 1915, solid massonry Chimeny, which is currently unlined and uncapped.

The furnace is 4" Type B Gas Vent pipe and it has a blower for the vent. This terminates at the chimney base.

Hot water heater, currently 3" galvanized pipe, increasing to 4" then terminating next to the furnace vent in the base of chimney. It is atmospheric vent.

My goal is to combine the two, converting the water heater to 4" type B pipe. I am replacing the water heater very soon, ie. within a week or two. The replacement calls for 3x4" vent pipe, I take that to mean either 3" or 4". I plan on going with 4" type B gas.

The questions:
1) Do I use a Y or a T to make this connection? I'm guessing a Y, is that correct?
2) when I share the vent does the vent pipe need to be up-sized? If it matters, I plan on buying a stainless flex liner to run up the chimney.
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Old 04-29-2013, 12:19 PM   #2
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Furnace/water heater vent pipe??


nothing against DIYers but chimneys can be dangerous if not installed properly and IMO should be left to a Pro. the liner has to be sized for the combined BTUs of the furnace and water heater and rise of chimney and there are local rules and regs on how they want it done as well as the gas code. there needs to be a cleanout/inspection port/fitting on the bottom according to code in some areas. I cannot go into that detail here. If you don't do it properly then the furnace can have pressure switch tripping problems and the water heater may not vent itself properly or could carbon up and produce CO and poison you and your family. chimneys can be dangerous if not done properly. you may also be liable in the future if someone gets hurt.

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Last edited by yuri; 04-29-2013 at 12:22 PM.
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Old 04-29-2013, 12:29 PM   #3
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Furnace/water heater vent pipe??


Btu's of furnace?
Btu's of HWT?
Length of vent pipe for furnace?
Length of vent pipe for HWT?
Diff in height between furnace vent outlet and chimney vent opening?
Diff in height between HWT vent outlet and chimney vent opening?
Height of chimney?

You definately need a liner with a power vented furnace. The HWT connection should be a Y but the vent sizing depends on your answers to the above questions.

As Yuri suggests
Best left to a pro who knows what your local jurisdiction is currently requiring.

Last edited by how; 04-29-2013 at 12:35 PM.
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Old 04-29-2013, 12:42 PM   #4
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Furnace/water heater vent pipe??


After doing some additional research. My Furnace is a Goodman 100-3, which is 20years old'ish'. So far it is doing well, but am guessing it's days could be numbered being that old, so maybe that should be taken into account....

With that, it appears to have an 80k BTU output so coupled with my water heater having a 40k BTU out, that puts me at about 120k BTU's. My chimney is, by my best guestimation, about 30-35' max. Accoding to what I see in the charts of the pipe manufacturer, Fan+Nat is 132k BTU into 4" pipe. So, I should be ok, unless someone reads anything differently. I'm looking at Met-Fab pipe.

As for yuri, I don't argue, which is why I had several highly reputable companies come out to give me bids, none wanted to do it and said I could tackle on my own. What else can a guy go???

Another thought is it looks like I could run the furnace out the side wall, but not sure if that is a good idea or not. Hmmm..... Guess may price that as well!!
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Old 04-29-2013, 12:46 PM   #5
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Furnace/water heater vent pipe??


I think you just answered some of your own questions. nothing against Goodman but they had heat exchanger failure problems with the mids awhile ago and if any furnace lasts 20 yrs nowadays then that really is the life expectancy of the exchanger unless you live in Calif and rarely use it. I would SERIOUSLY consider getting a high efficiency furnace soon and a elec water heater and abandon the NRG wasting chimney. or get a direct vent thru the wall gas water heater and high eff furnace. doing that chimney now is a complete waste of time and $$ IMO. that furnace most likely is not approved for sidewall venting, very few are with mids. if the chimney goes thru the centre of the house then lots of people remove them and fix the roof and the Wife/Boss will love the new real estate for closets or whatever.
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Last edited by yuri; 04-29-2013 at 12:51 PM.
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Old 04-29-2013, 02:33 PM   #6
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Furnace/water heater vent pipe??


Quote:
Originally Posted by yuri View Post
I think you just answered some of your own questions. nothing against Goodman but they had heat exchanger failure problems with the mids awhile ago and if any furnace lasts 20 yrs nowadays then that really is the life expectancy of the exchanger unless you live in Calif and rarely use it. I would SERIOUSLY consider getting a high efficiency furnace soon and a elec water heater and abandon the NRG wasting chimney. or get a direct vent thru the wall gas water heater and high eff furnace. doing that chimney now is a complete waste of time and $$ IMO. that furnace most likely is not approved for sidewall venting, very few are with mids. if the chimney goes thru the centre of the house then lots of people remove them and fix the roof and the Wife/Boss will love the new real estate for closets or whatever.
I will likely look into a new furnace soon, may see what they say at beginning of next season or better yet, have A/C serviced this spring/summer and have the furnace looked over so that I can plan....

Not sure I'm sold on the high eff stuff, but will definately weigh the pros/cons when the time comes. I don't see where an electric water heater would save any $$$, is that the new logic?? I could look into it and have room in my panel. I thought gas was lots cheaper than electric!

I priced a direct vent and it's more than double the cost of the atmospheric and they said the payoff is about 8-10 years, which is the life of a tank, they didn't seem to think it was a great solution or money saver, so I had written the idea off. I do agree it would be nice to go out the wall, but not sure 5 bills nice! I figure I pay $35 per month to heat my water in my 40gallon tank. Am I wrong to think 10% savings would only be about $3.50 per month?

Amazingly, through several home ownership changes of this house, I still have the original paperwork for furnace and it has Horizontal Venting Instructions and lists my model #. It says to use Hart & Cooley or Plexco vent material, wondering how expensive that stuff is. Is there anything to be gained in doing that, especially given the age of the system??

As for removing the chimney, it isn't going to happen, it is in center of house, but there is nothing to be gained as it has a bedroom wall on one side, a built in on the other and then the mantel sits at an angle on the other wall. On the 2nd floor it's in the attic and in the basement it would require ripping out concrete and concrete block and digging down 3-4' to gain any space!! Not to mention, how would Santa get inside???
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Old 04-29-2013, 02:53 PM   #7
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Furnace/water heater vent pipe??


To adjust your heat loss calculation.
The heat loss to your house with the chimney is not just the natural gas usage but the lost heated house air with a natural draft appliance..
The natural draft of a vent attached to that chimney is like leaving a window open 24-7.
You don't have to remove the chimney if it's too much hassle, just plug and insulate it enough to no longer be a cold sink once you don't need it .

Last edited by how; 04-29-2013 at 02:58 PM.
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Old 04-29-2013, 03:07 PM   #8
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Furnace/water heater vent pipe??


Btu's of furnace? 100,000
Btu's of HWT? 40,000
Length of vent pipe for furnace? 9-1/2'
Length of vent pipe for HWT? 5-1/2' existing opening 4-1/2' to furnace duct
Diff in height between furnace vent outlet and chimney vent opening? Furnace outlet at 2'8", chimney opening at 6', so approx 2'8" difference
Diff in height between HWT vent outlet and chimney vent opening? 59" to top of water heater, 6' to chimney opening, so 1'1"
Height of chimney? Stuck tape measure to it and it seems to be 24', I seem to have 3' in basement to bottom of subfloor, 9' main floor ceiling, 1' between floors, 7' in attic and 4' above roof line.

Quote:
Originally Posted by how View Post
You definately need a liner with a power vented furnace. The HWT connection should be a Y but the vent sizing depends on your answers to the above questions.

As Yuri suggests
Best left to a pro who knows what your local jurisdiction is currently requiring.
It looks like I'm right there at the cutoff. I am actually starting to wonder if I should just leave everything alone and wait out the furnace and see what happens in the next few years or whenever I decide to install a gas fireplace. The problem is I agree I probably should have a liner. My chimney top opening is about 9-1/2" x 10", so I could get two 4"-5" flex tubes down....
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Last edited by Master Brian; 05-07-2013 at 12:23 PM.
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Old 04-29-2013, 03:12 PM   #9
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Furnace/water heater vent pipe??


Quote:
Originally Posted by how View Post
To adjust your heat loss calculation.
The heat loss to your house with the chimney is not just the natural gas usage but the lost heated house air with a natural draft appliance..
The natural draft of a vent attached to that chimney is like leaving a window open 24-7.
You don't have to remove the chimney if it's too much hassle, just plug and insulate it enough to no longer be a cold sink once you don't need it .
Never thought about lossing heat out of the house through the water heater vent, but I guess there would be some. I'm guessing the power vent is the only way to stop that?

I just priced a small tank/high BTU unit and at near $2000 that's out!!
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Old 04-29-2013, 04:09 PM   #10
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Furnace/water heater vent pipe??


Quote:
Originally Posted by Master Brian View Post
After doing some additional research. My Furnace is a Goodman 100-3, which is 20years old'ish'. So far it is doing well, but am guessing it's days could be numbered being that old, so maybe that should be taken into account....

With that, it appears to have an 80k BTU output so coupled with my water heater having a 40k BTU out, that puts me at about 120k BTU's. My chimney is, by my best guestimation, about 30-35' max. Accoding to what I see in the charts of the pipe manufacturer, Fan+Nat is 132k BTU into 4" pipe. So, I should be ok, unless someone reads anything differently. I'm looking at Met-Fab pipe.

As for yuri, I don't argue, which is why I had several highly reputable companies come out to give me bids, none wanted to do it and said I could tackle on my own. What else can a guy go???

Another thought is it looks like I could run the furnace out the side wall, but not sure if that is a good idea or not. Hmmm..... Guess may price that as well!!

Venting tables use the input of the appliances, not the output.

Is your furnace a GMP? They are known to pop their crimp rings. Your furnace is probably way over sized.
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Old 04-29-2013, 04:53 PM   #11
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Quote:
Originally Posted by beenthere View Post
Venting tables use the input of the appliances, not the output.

Is your furnace a GMP? They are known to pop their crimp rings. Your furnace is probably way over sized.
Input is 100k BTU.

Why do you think it's oversized? Not to get off track, but....The house is about 2000sq ft, which is about 1300sq main floor, 1000sq ft unfinished basement(slowly becoming finished) and about 700sq ft 2nd floor.
The furnace doesn't vent upstairs, but of course heat rises.... Not to mention, when I bought the house, the walls were not insulated and single pane 100yr old windows with no real storms. About 40 windows on the house! I have done a lot to combat the draftiness of the old house, but adding storms, insulating, etc, but it's far from perfect!
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Old 04-29-2013, 04:54 PM   #12
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Furnace/water heater vent pipe??


elec tanks are popular if your elec rate is reasonable and in my expereince can last 50-100% longer than any gas tank. eliminates the need for a chimney and with a high eff furnace is what we do with 95% of my co. installs. there is no cheap way to heat water and yeah the tanks don't last but that's life. having a 3-4" vent from a water heater is like having a 3-4" hole punched in your roof leaking air/NRG/$$ out 24 hrs a day. direct vent is more expensive but does not lose air/$$. no perfect solution so you have to decide whats best for you. 80-90% chance the heat ex will fail soon so a new high eff. furnace that does not lose air up the chimney or use your expensive house air to feed the fire is a better idea.
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Last edited by yuri; 04-29-2013 at 05:09 PM.
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Old 04-29-2013, 06:08 PM   #13
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Quote:
Originally Posted by Master Brian View Post
Input is 100k BTU.

Why do you think it's oversized? Not to get off track, but....The house is about 2000sq ft, which is about 1300sq main floor, 1000sq ft unfinished basement(slowly becoming finished) and about 700sq ft 2nd floor.
The furnace doesn't vent upstairs, but of course heat rises.... Not to mention, when I bought the house, the walls were not insulated and single pane 100yr old windows with no real storms. About 40 windows on the house! I have done a lot to combat the draftiness of the old house, but adding storms, insulating, etc, but it's far from perfect!
Does it run 24/7 on the coldest nights.
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Old 04-29-2013, 06:19 PM   #14
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Furnace/water heater vent pipe??


I gotta add...


We went with a power vented NG water heater many years ago. Out chimney was in bad shape and needed to be relined, etc.

We opted for a Richmond 50 gal power vented unit and it has been great. Quick recovery, does fine with a family of 5, and vents thru an old window opening in the basement wall (as does our NG power vented boiler). At the local Menards up here the Richmond unit I have runs about $800.

I totally agree with the natural draft flue 'like leaving a window open' statement, especially in NW WI. It does make a difference despite the auto dampers and stuff I've seen.

Don't know if this info helps, but now that I've had both boiler and HWH with induced draft, I would definitely not switch back.
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Old 04-29-2013, 06:28 PM   #15
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Does it run 24/7 on the coldest nights.
I would like to say no, but to be honest our past few winters have seemed more mild, so I can't tell with the changes made.

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