As with many laws the wording is brief and is being interpreted incorrectly by many in the real estate industry. The law is RCW 19.27.530

The new carbon monoxide alarm rules went into effect April 1, 2012 and homes sold after that must have carbon monoxide alarms installed. The new law makes it the responsibility of the seller to install the carbon monoxide alarm(s).
- Carbon monoxide alarms must be installed adjacent to all bedrooms at least one per floor.
- Carbon monoxide alarms may be battery or hard wired.
- Carbon monoxide alarms may be combined with smoke alarms or installed independently.

Recently a client called me and told me that the home inspector who just inspected their home was calling for installing multiple CO alarms per floor. Obviously he was applying the  adjacent to each bedroom  rule liberally. The law does differentiate between new construction and existing homes. The RCW refers to the Washington State Building Code Council so I contacted Joanne McCaughan Code Specialist for clarification. Joanne said that the codes do not stipulate the size of the homes or the distance between the bedrooms. So the requirement is one per floor unless the manufacture of the alarms recommends otherwise. I spoke to Kidde technical support at and ask their recommendations for a larger home and they said you would only need one per floor. I can't fault the other inspector for wanting to exceed the Washington State RCW but he can't require the seller to do it.

For new construction the law requires a alarms outside of each sleeping area. So for example,  a large rancher that has a master suite on one side and several bedrooms on the opposite side of the home would require a Carbon monoxide alarm adjacent to each area.

What about home with lofts or unimproved areas? The law says one alarms per floor of the home regardless of whether their are bedrooms or living areas. So if that area is a "floor" of the home, it needs a CO alarms .

The new Washington law talks about installing the alarms adjacent to the bedroom so do you install a carbon monoxide alarms high on the ceiling or near the floor in a home? The short answer is: follow the installation directions that come with the alarms.

When considering where to place a carbon monoxide alarms, keep in mind that carbon monoxide is roughly the same weight as air so it really doesn't pool or rise. There had been confusion among that standards bodies as to where carbon monoxide alarms should be located but this was clarified in 2009. The National Fire Protection Association in its 2009 guidelines (NFPA 720 - 2009) no longer recommends that CO alarms  be mounted high in residential structures however they do recommend they be ceiling mounted in commercial structures. Here are other recommendations I found:
- Here is the CPSC page I found on CO http://www.cpsc.gov/cpscpub/pubs/466.html
- Kidde recommends "eye level" Here is a link to their installation guide http://www.kidde.com/utcfs/ws-...P-EN.pdf
The best and safest advice is read the directions that come with the CO alarm and install accordingly.

Last, but not least are all electric homes. One would think that since there are no sources of carbon monoxide that they would be exempt - Wrong! Same rules apply. After the December 2006 windstorm raged across the region, more than 300 people were sickened, and eight were killed by carbon monoxide as families without electricity turned to alternate sources of heat and power. The legislature was smart to apply the same rules to all existing homes.

Facts about Carbon Monoxide Poisoning


Auto exhaust is thought to be the number # 1 cause of accidental CO poisoning in North America and has been reported to be the cause of around 60% of carbon monoxide alarm responses. Just notice how many people let their automobiles warm up inside garages with the door open and for how long before they back out and close the door with their automatic door control. Typically, any gasoline engine produces the highest CO levels during a cold start. CO gets trapped inside the garage and can easily disperse into the rest of the building through unseen but loose fitting construction connections (like wiring penetrations, framing joints, ductwork seams, door jambs and other areas). Building pressure and temperature variations work as siphon points and air exchange locations.

Every home should have a CO alarms. There are inexpensive and available at most home improvement stores. CO alarms come in many styles and range in price from under $20 to over $75. Generally the cheaper models only sound the alarm while the more expensive models will sound an alarm and display the CO level. Consumer Report’s tested CO alarms in October, 2001 and recommended models from Kidde and Senco as having superior performance.

Proper placement of a carbon monoxide alarms is important. If only installing one carbon monoxide alarms, the Consumer Product Safety Commission (CPSC) recommends it be located near the sleeping area, where it can wake you if you are asleep. Additional alarms on every level of a home will provide extra protection.

Carbon monoxide in homes does not always come from traditional sources. The service and HVAC industry has been targeting cracked heat exchangers as the leading source of CO poisoning (almost exclusively without test instrument verification until about 1985). Recent, more thorough testing for CO suggests that unvented, poorly installed, unmaintained and misused gas and oil appliances are the 2nd leading cause of CO alarm response, and may constitute as much as 20% of CO alarm call sources.

The 3rd leading cause of CO exposure appears to be due to vented atmospheric, natural drafting appliances which backdraft into the structure and may account for 19% of the CO alarms going off. Intermittent backdrafting of CO laden flue gases complicates source investigations. Improperly sized and installed vent systems, old vents in need of repair, and competing building pressures contribute to this affect. Even if no significant levels of CO are measured in the flue gases, keep your eyes open to indications that spillage is occurring during other periods of time. Soot or rust on draft hood surfaces or above the burner areas are common examples.

It should be noted that cracked heat exchangers make up one of the smallest percentages of CO alarm response causes (less than 1%). Unfortunately as furnace get older and receive little maintenance the opportunity for a crack grows larger. In many cases the HVAC technician only does a visual inspection of the furnace heat exchanger not knowing that the crack most often happen on the backside of the exchanger. The only certain way to check the heat exchanger is to have it leak tested.  In some cases a furnace with a cracked heat exchanger is condemned by a technician or utility personnel, red tagged and shut off only to be returned to operation by a homeowner. A furnace left in operation while a known crack exists represents a tremendous health, safety and liability concern and should be thoroughly tested for CO production. Test results can then be presented to the homeowner emphasizing a very real and present danger.

These are some general guidelines for carbon monoxide alarms common to most manufacturers:

• Alarms should be placed on every level of your home, including the basement, and near or over any attached garage.
• They should be located within 10-15 feet outside of each separate sleeping area.
• Alarmscan be placed on the wall or the ceiling as specified in the installation instructions.
• Do not install alarms within 15-20 feet of any furnace or fuel burning heat source.
• Alarms should not be placed in or near humid areas, such as bathrooms.
• Place alarms in areas where they will not be damaged by children or pets.
• Do not install alarms in direct sunlight or areas subjected to temperature extremes. (crawlspaces, unfinished attics, porches)
• They should not be installed behind curtains or other obstructions.
• Alarms may not function as designed if installed near ceiling fans, heat vents, air conditioners, fresh air returns, or open windows.
• Life expectancy for alarms will be specific to each manufacturer’s recommendations. Carbon monoxide alarms actually have an expiration date, so check with the manufacturer instructions to determine how long the carbon monoxide alarms is supposed to last and maintain your specific unit accordingly.

Pacific Crest Inspections is a locally owned home inspection company providing home inspections, commercial inspection and pest inspections in the Bellingham, Wa. area. Pacific Crest inspections is a Licensed Home Inspector in Washington State and carries the highest certification “Certified Real Estate Inspection” offered by the American Society of Home Inspectors (ASHI)  Pacific Crest Inspections conducts their Washington State home inspections according to the Washington State Home Inspectors Standards of Practice & Code of Ethics. These professional home inspection standards provide a minimum guideline for conducting a Oak Harbor, Washington home inspections. Our home inspection standards are available for viewing under the "Consumer Information" section of our website or ask your Washington  home inspector for a copy of the Washington home inspections Code of Ethics prior to your Bellingham home inspection.