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Renaissance Man
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6,818 Posts
I reline tons of chimneys - older homes mostly masonry/terracotta chimneys. Standard protocol is stainless liners sized to the BTU input, run to stack and chimney elevation. Typ. 3" or 4" usually does the job.

Orphaned water heaters will destroy a 9x9 flue in short order in any cold climate.
 

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manipulator of wood
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835 Posts
when the furnace is disconnected from the chimney,leaving the water heater alone, thus an orphan
 

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PCI
General Contracting
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670 Posts
These have potential to back draft because there is no furnace exhaust drawing up the emissions. So if the furnace doesn't run (summer months) and there is negative pressure in the house say from two bath fans and a kitchen exhaust fan on the flue can back draft. Now you have CO filling the house. We always do a pressure test to see if we have to install a direct vent with the furnace install.
 

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Holder of hands
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680 Posts
The furnace isn't running in the summer time anyway, I guess I don't see why a new problem is being created. If the wye is capped off, why isn't that good enough? If it's back drafting, wouldn't a power vent eliminate that problem? I just guess I haven't run into that issue yet. You still have combustable air ducts to feed the water heater, right?
 

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PCI
General Contracting
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670 Posts
Where it has come into play for us is when there was a orphaned water heater when we arrived. We did a kitchen remodel and added a huge over the range vent and this particular development used a exhaust fans on the second level for an air exchanger.

The additional negative air pressure from our exhaust hood, combined with the air exchanger on, created a draw from the flue.

There are other ways to fix this problem, but the water heater was 10 yrs old. Doesn't happen a lot, but once can kill.
 

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PCI
General Contracting
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670 Posts
A short aside to CO, we just replaced a red tagged gas range for excessive CO, actually the oven portion. Occupants kid kept getting sick. Finally the CO detector went off, fire dept came, police came and gas company red tagged the oven but ok to use the cook top. Who knew that an oven could do this?
 

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Holder of hands
Joined
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680 Posts
Where it has come into play for us is when there was a orphaned water heater when we arrived. We did a kitchen remodel and added a huge over the range vent and this particular development used a exhaust fans on the second level for an air exchanger.

The additional negative air pressure from our exhaust hood, combined with the air exchanger on, created a draw from the flue.

There are other ways to fix this problem, but the water heater was 10 yrs old. Doesn't happen a lot, but once can kill.
Yeah, I get it when you add a commercial type hood. But then, you need to introduce another air source to compensate for the loss of air inside the house. In that case, you are creating a new problem that needs to be solved.
 

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Contractor of the Month
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26,075 Posts
I reline tons of chimneys - older homes mostly masonry/terracotta chimneys. Standard protocol is stainless liners sized to the BTU input, run to stack and chimney elevation. Typ. 3" or 4" usually does the job.

Orphaned water heaters will destroy a 9x9 flue in short order in any cold climate.
Why is that? I replaced my furnace a few years ago with a condensing furnace and just capped off the wye.
 

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Spec-Pro
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22 Posts
Discussion Starter #13
Stack effect is very important for a home. For instance, we have had clients that have sealed up their house as tight as humanly possible and then they wonder why their wood burning fire place does not work. If negative pressure is created in your home, then it is a problem.

Most stack effect in the average water heater system with a draft hood is measurable to less pressure than we use to suck water through a straw, so even a little bit can cause that CO to enter the home.

The short end of it, I believe an orphaned water heater should not exist in a home since it is such an easy thing to fix and such a potential danger.
 

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Spec-Pro
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22 Posts
Discussion Starter #14
BTW - Most people don't think it is a problem because their CO detector does not go off. Most CO detectors won't go off until it gets to about 30 ppm or more, but the ill effects of CO starts at about 9 ppm (the math is easy there). And if your CO detector is on another floor than your water heater, the levels need to get even higher before it sounds the alarm.

Check the detection level on your CO detector, it may surprise you....
 

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Sean
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5,495 Posts
Eventually I am going to get that piece on CO up but a UL Listed (what we are mandated to install) does not go off until you hit around 70 ppm and that is after X amount of time (20 mins?). A house could stay at 30 ppm forever & it would not ever go off.

PCI - oven brand new out of the box tested @ 800 ppm... Up to 200 as I recall is deemed acceptable by manufacturers (thats one of the real reasons you need a real oven hood that vents outside)

For a real eye opener & some great info on all things HVAC - http://ncidavid.blogspot.com/2011/11/thanksgiving-gas-ovens-and-carbon.html
 

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Spec-Pro
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22 Posts
Discussion Starter #17
Most of the units I have purchased and researched online all said a minimum detection limit of 30 ppm. Some of them do have a higher limit. Below is a quote from one of the spec sheets of a Kiddie:


"70 ppm (parts per million) of CO for 60 to 240 minutes, 150 ppm for 10 to 50 minutes, or 400 ppm for 4 to 15 minutes"

Either way, that's pretty scary.....
 

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Registered
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2,502 Posts
Where it has come into play for us is when there was a orphaned water heater when we arrived. We did a kitchen remodel and added a huge over the range vent and this particular development used a exhaust fans on the second level for an air exchanger.

The additional negative air pressure from our exhaust hood, combined with the air exchanger on, created a draw from the flue.

There are other ways to fix this problem, but the water heater was 10 yrs old. Doesn't happen a lot, but once can kill.
The problem your describing is the range hood your installing, not the water heater. Most places that sell those large range vents also sell them a make up air system.
 

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Registered
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2,502 Posts
I run into a lot of orphaned water heaters in my area. What do you think is the best way to fix it, a direct vent or a power vent?
Reline the chimney.

Nat draft water heater with a 3" breech by code can't be vented into a chimney with an area greater then 49 sq in.

With a 4" breech, 87.9 sq in.

Lining a chimney is often cheaper then installing a new indirect, or power vent system.
 

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Holder of hands
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680 Posts
Here you need combustable air for any gas fired heating unit. I assume it's the same everywhere. Here we would be installing two 6" outside air pipes and dumping them at the Hot water heater, one high and one low, assuming it's a B vent type HWH. That should eliminate any negative pressure, except maybe from a commercial range hood. Maybe I am missing something, but I still don't see the problem.

I don't claim to be a HVAC expert, but I just don't hear of any problems where combustable air is properly introduced, even with wrapped houses, and that code has been around for awhile.

The obvious answer to that senario is to change out the HWH to a more efficent pvc vent type with it's own sealed combustable air source.
 
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