CO and smoke detectors

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olly

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Berthoud, Colorado
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Master Electrician
Could someone please tell me what the requirements are for where CO detectors need to be located. I think CO is heavier than air so are plug in detectors the way to go? I will be installing/upgrading this for a guy that is selling his house so the cheaper option is prefered. Do you have to change out the smokes if they are older than 10 years to sell the house? Thank you!
 
olly said:
Could someone please tell me what the requirements are for where CO detectors need to be located. I think CO is heavier than air so are plug in detectors the way to go? I will be installing/upgrading this for a guy that is selling his house so the cheaper option is prefered. Do you have to change out the smokes if they are older than 10 years to sell the house? Thank you!
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NFPA 72, manufacturers instructions, building code/ahj etc will give you that info.
 
CO mixes with air very well, if you read instructions they can go just about anywhere, unlike smoke detectors that should be mounted high because smoke is usually going to rise. They may recommend staying away from "dead air" spaces that don't see much change like in corners or partitioned off areas.
 
161228-1604 EST

See http://www.engineeringtoolbox.com/gas-density-d_158.html for one source of densities. It was not specified but my assumption is STP (Standard Temperature and Pressure) conditions.

CO is in the ball park of air and possibly slightly less dense based on the average figures given. Whereas CO2 has an average density greater than air. But there is not a great deal of difference. Whereas helium has a gross difference and hydrogen even greater.

Do a search on --- density of air CO CO2 ---

Air flow will have a great affect on how the gases mix.

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The most common thing we are concerned with introducing CO is a failed heat exchanger on HVAC equipment. Often involving fan forced air heating systems. The fact the source is coming from moving air that is being distributed all over the home mixes it well.

If you have a failing water heater as the source then the higher concentration will be in the vicinity of the appliance. Still if you a have forced air HVAC system it will distribute it everywhere if it should be introduced into the return air.
 
I'd call the agency doing the inspection. Here in MA a smoke certificate is required to close on a dwelling. Inspection by local FD. While we have a state regulation, every department enforces differently, so it is worth the phone call to talk to the fire inspector to get these answers. And here, if they are 10 years old they must be replaced, but not every town enforces that.
 
The 2015 International Residential Code requires CO detectors to be installed outside each sleeping area in the immediate vicinity of the bedrooms. Where a fuel-burning appliance is located within a bedroom or its attached bathroom, a carbon monoxide alarm shall be installed within the bedroom.

Utah has amended this section to also require a CO detector on each habitable level even if there is no sleeping unit on that level.

Chris
 
olly said:
Could someone please tell me what the requirements are for where CO detectors need to be located. I think CO is heavier than air so are plug in detectors the way to go? I will be installing/upgrading this for a guy that is selling his house so the cheaper option is prefered. Do you have to change out the smokes if they are older than 10 years to sell the house? Thank you!
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I believe mandatory on every floor is minimum -- if the bedroom has a fuel burning appliance/fireplace then inside that room is required -- If you are able to hardwire connect during remodel that can be enforced (and is preferred) but battery op & plug ins are acceptable in some cases -- check with your local AHJ -- wall & ceiling locations are specified by installation instructions -- from what I've read CO height levels are determined by ambient temp -- warm it is lighter than air & cool it is heavier than air so Most of the time indoor condition spaces would have it lighter than air IMO
 
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