Reuben's Home Inspection Blog


Houses Don't Need C02 Alarms

There are many common misconceptions about furnaces, water heaters, and carbon monoxide that I hear repeated on a daily basis, and I'd like to clear a few of them up.   


False: Carbon Monoxide is also called CO2.  Carbon Monoxide is CO. Carbon Dioxide is CO2.  (Mono = 1, Di = 2)


False: Cracked heat exchangers create CO.  CO is caused by incomplete combustion, period.  A cracked heat exchanger does not create CO.  A heat exchanger is the part of a furnace that transfers heat from the flames to the household air.  A functional heat exchanger keeps the household air and the combustion gases completely separate from each other.  If a furnace has a cracked heat exchanger, the combustion gases can mix with the household air.  It's usually just a little bit, but this is still unacceptable, and it means the furnace or heat exchanger should be replaced.  The photos below show cracks in heat exchangers (click the photos for full-sized images).

Cracked Heat Exchanger #1   Cracked Heat Exchanger #2  Cracked Heat Exchanger #3  Cracked Heat Exchanger #4


False: Cracked heat exchangers can be fixed.  They can't be fixed.  The heat exchanger or entire furnace needs to be replaced.


False: High CO levels = cracked heat exchanger.  See above.  We test the CO levels in the flue gas, which has nothing to do with a cracked heat exchanger.  Heat exchangers fail when the metal rusts through or when it cracks.  CO does not cause this.


False: High CO levels in the flue gas mean the furnace is leaking CO.  If there is a high level of CO in the flue gas, there is a potential for the exhaust gases to mix with the household air, or ‘leak'.  One way would be for the exhaust gases to backdraft, which means that instead of rising up and out of the house, they come back down the flue.  The other way would be because of a cracked heat exchanger.  If we find high levels of CO in the flue gas, we recommend immediate repair - it doesn't matter if the gases are mixing with the household air at the time of the inspection or not, because this condition could potentially change at any time.  Higher CO levels can often be fixed.


False: Backdrafting at a furnace or water heater means CO is coming in to the home.  Backdrafting means that exhaust gases are spilling back in to the home, rather than going up the flue.  A properly functioning water heater or furnace will not create CO, so you can't say CO is coming in to the home unless you test the exhaust gases; we do this at every inspection.  Click here for a news clip me testing a furnace.  While backdrafting doesn't mean CO is coming in to the home, this is still a potentially hazardous situation that requires immediate correction.  Backdrafting has the potential to allow CO in to the home, and will always contain CO2 (carbon dioxide), which can cause sickness and headaches in higher concentrations.


Wrong Term: Hot water heater.  Just 'water heater'.  The heated water that comes out is hot.


To summarize, high levels of CO need to be fixed, cracked heat exchangers need replacement, and backdrafting is never ok.  These three things are all independent, but a combination of these conditions is especially dangerous.  When using these terms, make sure you have them correct.  It makes a difference.

Reuben Saltzman, Structure Tech Home Inspections - Email - Minneapolis Home Inspections  



Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 13 commentsReuben Saltzman • March 08 2009 07:34AM


I look forward to the valuable information your always passing along.


Posted by Deanna Casalino, Fort Myers Florida Homes, (Remax Realty Group) over 11 years ago

MORNING REUBEN!  Great stuff.  What is the appropriate place to place a CO2 detector to get a reading?  I've had inspectors place them right on the furnace, at the air vents and on the floor.  And if a home gets a reading of a one - is that considered enough to replace?  Thanks!  -- Gabrielle

Posted by Gabrielle Kamahele Rhind, Broker/Owner (KGC Properties LLC, Tucson Property Management & Real Estate) over 11 years ago

Deanna - Thanks!

Gabrielle - Bite your tongue! (insert winking smiley face)  Here in Minnesota, CO alarms are required within ten feet of every sleeping room, so this is where I recommend placing them.  I don't get picky about exactly where, as long as this rule is followed.  Not on the furnace though.  If a CO alarm gets a high reading, the cause of the high reading should be determined and corrected.  There is no need to replace the CO alarm.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago

Thank you again for more great information.  I wish everyone could explain these issues so clearly.  This is great reference material.

Posted by David Henke, Realtor, Homes Just West of Philadelphia PA (Long & Foster Real Estate, Inc) over 11 years ago

Rueben very nice post; informative and well though out.  If only all home inspectors were as detailed oriented as you obviously are. 

Posted by Larry Story, Total Care Realty, LLC, Greensboro, NC Real Estate (Total Care Realty) over 11 years ago

Reuben---good and accurate info for people.  I am always amazed that people equate the burning of gas with Carbon Monoxide.  While there are a host of reasons why your kitchen range should be vented outdoors, carbon monoxide is rarely considered one of those reasons, and they are allowed to be operated in the home without venting.  I personally think it is a good idea to vent them due to the remote possibility of improper combustion which might lead to carbon monoxide----but it is not "required."  A lot of factors have to be in place to get carbon monoxide in the home.  The problem is that when it happens----people die, so it is a really good idea to report on conditions that can lead to it:)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 11 years ago

Thanks all!

Charles - I even saw a home inspector on HGTV equate burning gas with carbon monoxide.... unbelievable.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago

Actually, "hot water heater" is an acceptable term. Here's why:

Water heaters come with a thermostat. Typically those thermostats have little dashes on them below HOT on one side and WARM or VACATION on the other. Some have letters -- A B C D E. Some electric ones have the actual temperature. There's a big dash or some other marking that indicates the recommended setting. That recommended setting is usually 125°F.

Cold water that comes into the water heater is somewhere around 70° if one is lucky, usually much colder. The water is then heated to whatever the thermostat setting is. Let's say that it's set at 125°F. The user guide for my old replaced Richmond water heater (went to tankless) says that each dash is approximately 10°F. So once the water is heated to 125°F, the burners cut off. If that water then falls to 115°F, the burners come back on and heat the water back up to 125°F. The thermostat tries to keep the water at the desired temperature all the time because it doesn't know when I'm going to need it. Now I don't know about you, but I consider 115°F water to be very hot, indeed. So that water heater is, indeed, heating hot water (115°F) to an even hotter temperature (125°F). Ergo, hot water heater is acceptable.

Posted by Jim Frimmer, Realtor & CDPE, Mission Valley specialist (HomeSmart Realty West) over 11 years ago

Jim - I get your point... but how about Cold Water Cooler?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago

Finally! It is great to see someone that is debunking the myths behind CO. Great post Reuben!

Posted by Randy King (Prokore Inspections) over 11 years ago

Reuben -I think you need to post this at least every two months.

Jim - Hot water heater is redundant and not acceptable. :) 

Posted by Steve Hall, Make the Call to Hankins and Hall (RE/MAX United) over 11 years ago

Steve - thanks, maybe I will.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago

I see Jim's been over here and that he learned well when he was a home inspector -- LOL.

Posted by Russel Ray, San Diego Business & Marketing Consultant & Photographer (Russel Ray) over 11 years ago