Furnaces made in the last 30 years (65% to 80% AFUE furnaces with air-conditioning installed) have no chance of putting carbon monoxide in your home because of a cracked heat exchanger.
Contrary to what you've been told (and most of the stuff you read online), a cracked heat exchanger does NOT put, let, cause CO to enter the indoor air stream for your home. (This applies to a specific style of upflow and horizontal furnace used in residential forced-air systems. It also happens to be the most frequently installed configuration.)
There may be other problems with your furnace or heating system, but carbon monoxide from a heat exchanger crack won't be one of them.
The public and even HVAC mechanics, have been systematically misinformed for years.
For the skeptical technicians out there, pay attention. You've been given bad information. Read "How Not to Find Cracked Heat Exchangers".
Something that started out as a valid warning (in the '1940's and '50's) has been carried to such an extreme that it has spawned myths and half truths about modern gas furnace operation, carbon monoxide and safety.
It seems nobody has been paying attention as the design of furnaces has changed over the years. Or, more likely, the safety and testing agencies have taken the view that it is better to scare the consumer and keep them safe than to admit that a minor heat exchanger crack isn't the end of the world.
They've managed to write these wives' tales into local ordinances and gas utility company operating procedures. The net result has been increased costs and inconvenience to consumers. It has caused premature equipment replacement, delayed real estate transactions, difficulty getting occupancy permits and, most importantly, a potential disregard for real circumstances that affect gas equipment safety in the home.
The whole point of this web site is to make you aware of the fact that many circumstances in your home can and will make your gas appliances unsafe, and that small heat exchanger cracks aren't the problem they are portrayed to be.
This "baloney" has been going on for years. They teach it in schools, they write it into local ordinances, they pontificate about it at seminars and scare the devil out of homeowners with it - which is the entire point. To make consumers so scared of heat exchanger cracks that they'll gladly turn over thousands of their hard earned dollars to stay safe and protect their families. The tragedy is that scare tactics don't change facts.
People still die because of carbon monoxide.
They don't die because of little heat exchanger cracks, they die because of big cracks or other problems with the heating system and how it is operated.
Who am I?
Who am I to buck hundreds of other contractors and web sites who insist that any kind of hole or crack or defect in a gas-furnace heat exchanger is a danger that has to be shut down immediately?
Although I have 30+ years in the heating and cooling business, I don't have an engineering degree and I don't sit on the boards of any of the rating agencies. I also don't have a financial interest in furnace manufacturers or controls manufacturers or the contracting business. However, I do pay attention and I do ask questions and I go to reputable sources for information. I find that in many cases you have to "read between the lines" to understand how and why information is presented in certain forms and why the stated "conclusions" don't always match the evidence.
Here are some questions to think about: