What is considered to be a safe level of carbon monoxide?

Why does it say not to use carbon monoxide alarms in furnace rooms?

• Not two long ago all the smoke alarms and carbon monoxide alarms in our house became over ten years old. So we replaced the smoke alarms in some rooms with ones that had visual indicators on them as well as beeping. However on each level we also made sure that there was at least one smoke alarm that also functioned as a carbon monoxide alarm. One of these smoke alarms that can also function as carbon monoxide alarm is in the furnace room we just figured that if the inducer motor to our furnace ever cracked or the water heater flue ever rusted through or there was a backdraft for some reason that carbon monoxide would be picked up in that area. But then I started reading all these things online about that you should never have any type of carbon monoxide alarm in the furnace room. Why is this? I have never had a problem with any type of carbon monoxide alarm that has been located in the furnace room and we have always had some type of carbon monoxide alarm in the furnace room since we lived here. Can you please explain?

• Answer:

  I suppose as with any else these days, your going to get conflicting advice. I just read an article that said to put one in the furnace room. I don't see how it can hurt not to.