Article Says Cracked Heat Exchanger Will Not Put CO Into The Indoor Air Of A Home. - HVAC - DIY Chatroom Home Improvement Forum
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Old 02-11-2017, 05:52 PM   #1
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Article says cracked heat exchanger will not put CO into the indoor air of a home.


http://carbonmonoxidemyths.com/myths/myth-1/


This link below is the source of the information contained in the article/link above:
http://www.achrnews.com/articles/872...-installations Scroll down near the bottom of page for the article titled: Sidebar: CO Article Correction

What about this?

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Old 02-11-2017, 06:32 PM   #2
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


About 10 years ago the HVAC guys came by to do an annual cleaning on my old furnace (about 25 years old) and told me that I had a cracked heat exchanger and needed a new one specifically due to the possibility of CO getting in the ducts. Still glad I got a new furnace though.

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Old 02-11-2017, 07:27 PM   #3
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Its right and wrong.

Since the heat exchanger has a positive pressure on the outside of it. CO is not put into the air when the blower is on. And usually not even with just the inducer running before the fan starts.

However, many 80% furnaces have the air filter access right at the furnace, and it is not sealed. The blower can draw CO back through the burners, and put CO into the house.
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Old 02-11-2017, 09:26 PM   #4
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


if air is leaking into the heat exchanger i'm sure it could mess with combustion and cause high co in the exhaust.

or worse, flames and exhaust being blown out of the heat exchanger burner inlets.
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Old 02-12-2017, 09:26 AM   #5
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


The gas code where I am says if there is a crack and you get flame disturbance then the heat exchanger must be replaced.

Air gets thru the crack and forces the flames to rollout the front and spill fumes into the house once it gets bad enough. That is why we have "wait for it" ROLLOUT switches.

Either way a cracked heat exchanger is dangerous.

As for telling Joe Public/homeowner of the reasons none will understand a long technical story so we use the CO story.
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Old 02-12-2017, 09:07 PM   #6
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


The link in the first post suggest that the increased pressure from the blower motor would blow indoor air air into the combustion chamber, thereby making it impossible for CO to enter in the opposite direction. While this is appealing, it does not take into account a possible venturi effect at the crack, which would "suck" combustion gasses into the indoor air supply. Theory is no match for data and measurements. Anybody know if this has been thoroughly investigated or measured?
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Old 02-12-2017, 10:27 PM   #7
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by justplumducky View Post

What about this?
Ever wonder why when you get a hole in your tire, the air always leaks out instead of in?

It's all about pressure. A gas will always flow from a higher pressure zone to a lower pressure zone.

As long as the pressure remains higher on the air side of the exchanger, you will not get CO leaking in. Indeed one of the safety design features of residential forced air furnace (as compared to a commercial power plant) is to make sure the exhaust side of the exchanger always runs at the lowest pressure possible. In other words the exhaust blower is on the outlet side of the exchanger. As a result the exchanger always runs at a slight vacuum so pressure will always be lower.... even when your air blower is off.

If the crack is big enough (or you get enough small cracks) then of course all bets are off, but for the most part, the odd small crack is not dangerous.

Having said that though... I wouldn't bet or risk my family's life on it. If it's cracked and you are aware of it THEN CHANGE IT.
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Old 02-12-2017, 10:34 PM   #8
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by sktn77a View Post
The link in the first post suggest that the increased pressure from the blower motor would blow indoor air air into the combustion chamber, thereby making it impossible for CO to enter in the opposite direction.
Well, if the crack gets big enough and is close enough to the exhaust fan then exhaust can start backing up and coming out the inlet where the flame is. One would figure though that this would cause a big enough interruption in the flame pattern so that your overheat limit switch would start getting licked by the odd flame and eventually kick out.
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Old 02-13-2017, 04:10 AM   #9
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by sktn77a View Post
The link in the first post suggest that the increased pressure from the blower motor would blow indoor air air into the combustion chamber, thereby making it impossible for CO to enter in the opposite direction. While this is appealing, it does not take into account a possible venturi effect at the crack, which would "suck" combustion gasses into the indoor air supply. Theory is no match for data and measurements. Anybody know if this has been thoroughly investigated or measured?
Keep in mind that on induced draft appliances. The inducer is creating a negative pressure in the heat exchanger to begin with. So a venturi effect is only minimally possible. Specially, on any furnace that has an A/C coil on it. As this creates a higher static pressure around the heat exchanger.

Anytime I have read CO in a supply duct, the return duct had also had CO in it, and the blower compartment read higher then the return duct. Indicating it was being drawn out of the burner compartment into the filter opening.
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Old 02-13-2017, 08:21 AM   #10
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


All I know is when Dee started to complain about headaches when she was in the house. After she nagged me enough, I called the gas company. As they walked to the house, their gas detector tripped. There was so much CO, they shut off the gas to my furnace. A new furnace, some new ducts and her headaches stopped. Peace returned to my home.
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Old 02-13-2017, 02:27 PM   #11
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by fireguy View Post
All I know is when Dee started to complain about headaches when she was in the house. After she nagged me enough, I called the gas company. As they walked to the house, their gas detector tripped. There was so much CO, they shut off the gas to my furnace. A new furnace, some new ducts and her headaches stopped. Peace returned to my home.
There are many ways co can work its way in and wreak havoc with your health and well being. Indeed the only REAL way to protect yourself is get rid of the gas altogether and heat with electricity or similar. The wife and I don't use gas anymore.... don't like it at all. Of course that's not very practice for some so the next best thing are CO detectors... and not just one either because you never really know if it's a dud or not. You're best to put a few of them up.
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Old 02-13-2017, 02:56 PM   #12
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Carbon monoxide alarms offer minimal protection from chronic low levels. They only go off above 70ppm and even at that level, not for several hours.

The UL standards are designed to make it easier for fire departments - fewer calls.

You can go a step further and get an alarm with a display that reads down to 20ppm.

There are also non-ul low level monitors.

---------
When it comes to risk, modern sealed combustion furnaces are incredibly safe.

CO or flame can't spill out and are contained. They have lots of safeties.

The biggest risk they pose is producing high levels in the exhaust if there's a combustion problem, and the exhaust vents out the exterior wall of the house. If 1000 ppm co is being put out the side of a house it's worse than idling a car around the same area - some is bound to get in.

Attached garages and natural draft appliances pose the greatest risk.

Gas ovens can be dangerous.

If you take precautions with gas, it's safe. It's cheaper and better environmentally than electricity if your electricity comes from fossil fuel plants; with electric heat you need 2-4 times the BTU input at the power plant to get the heat compared to condensing gas.
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Old 02-13-2017, 03:30 PM   #13
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by fireguy View Post
All I know is when Dee started to complain about headaches when she was in the house. After she nagged me enough, I called the gas company. As they walked to the house, their gas detector tripped. There was so much CO, they shut off the gas to my furnace. A new furnace, some new ducts and her headaches stopped. Peace returned to my home.
Glad to hear its taken care of.

A CO detector won't go off while they are walking up to your house. If your house had a high enough level of CO in it to be detected as they walked up. That would mean you are a ghost, as the CO level in the house would have been in the "lethal in a few minutes exposure range"(in excess of 10,000PPM/greater then 1%) to be detected outside of the house.

However, there is a very good chance you had a gas leak. And that could be picked up outside near the house.
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Old 02-13-2017, 04:10 PM   #14
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


99% of the CO poisoning incidents I see or hear of are caused by partly blocked chimneys or downdrafts in them causing fumes to spill out the front of gas water heaters and older natural draft furnaces.

Most modern furnaces have spill switches in front of the burners in case fumes get pushed out by a cracked heat exchanger.

Fireplaces have NO safety controls for that and are dangerous and can kill people if not taken care of properly.

Have never had a high efficiency furnace cause CO poisoning and once you get rid of chimneys it is pretty rare.
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Old 02-13-2017, 04:40 PM   #15
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Re: Article says cracked heat exchanger will not put CO into the indoor air of a home


Quote:
Originally Posted by yuri View Post
99% of the CO poisoning incidents I see or hear of are caused by partly blocked chimneys or downdrafts in them causing fumes to spill out the front of gas water heaters and older natural draft furnaces.

Most modern furnaces have spill switches in front of the burners in case fumes get pushed out by a cracked heat exchanger.

Fireplaces have NO safety controls for that and are dangerous and can kill people if not taken care of properly.

Have never had a high efficiency furnace cause CO poisoning and once you get rid of chimneys it is pretty rare.
Question for you Yuri...

Regarding CO poisoning. Of course I understand that this has happened before and every care is not enough to protect lives. My question is technical only.

Chemistry-wise:
CO is a product of an incomplete combustion. A complete (and therefore more efficient) combustion only results in Water and CO2. A poor combustion generates amounts of CO together with the other two. A very poor combustion generates Carbon (C) with a higher amount of CO than the situation before, and still H2O and CO2.

In this case doesn't it make sense that the amount of CO that **SHOULD** be being produced by a properly maintained and cared furnace would be negligible, and in this case even if fumes get circulated to the house the amount of CO should be minimal (enough to not even trip an alarm)?

Also, one of the main reasons for an incomplete combustion is lack of fresh air. this can happen easily on a draft style heater/furnace with a clogged stack when the fumes will come back to the flame air make the actual amount of available Oxygen to not be enough for a complete combustion.

If you think like that, a high efficiency vented device will never operate without enough air to allow for complete combustion (it will trip a sensor if either the intake or exhaust are clogged). In this case it is virtually impossible for he furnace to generate CO at dangerous levels anyway.

I get confused as people always talk about CO, but in the first place that shouldn't even be produced by the flame..

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