• Carbon Monoxide – What You Need To Know

    What is Carbon Monoxide (CO)?

    • CO is a colorless, odorless, tasteless gas
    • It is a by-product of incomplete combustion (unburned fuel such as gas, oil, wood, etc.)
    • Low concentrations of CO can go undetected and can contribute to ongoing, unidentified illnesses. At high concentrations, it can be deadly.

    Why is it Dangerous?

    If there is CO in the air you breath, it will enter your blood system the same way oxygen does through your lungs. The CO displaces the oxygen in your blood, depriving your body of oxygen. When the CO displaces enough oxygen, you suffocate.

    What are the Symptoms?

    Continued exposure or high concentrations can result in –

    • Confusion
    • Severe headaches
    • Cardiac problems
    • Breathing difficulties
    • Brain damage
    • Dizziness
    • Death

    Long term exposure to low concentrations –

    • Slight headaches
    • Fatigue
    • Shortness of breath with only moderate exertion
    • Nausea
    • Dizziness and confusion

    Why is it called "The Great Imitator"?

    • Symptoms of CO poisoning are very similar to the flu
    • Illness in pets preceding illness in a family member may suggest CO poisoning

    Who is at Greater Risk?

    • Senior citizens
    • Unborn babies
    • People with respiratory or coronary problems
    • Infants
    • Pregnant women
    • Young children

    Note: Vulnerable people who are exposed even to low levels of CO for long time periods may have similar health affects as those exposed to high concentrations of CO.

    What can Produce CO in our Homes

    Anything that burns fuel or generates combustion gases including -

    • Gas Stoves
    • Fireplaces
    • Automobiles
    • Barbecues
    • Furnaces
    • Ranges
    • Boilers
    • Space heaters
    • Water heaters
    • Portable generators

    Solid fuels, such as wood, always produce carbon monoxide when they are burned. Gas and liquid fuels may produce no CO or very little.

    What are the most common sources of Carbon Monoxide?

    1. Automobile exhaust in attached garages.
    This is responsible for 60% of all CO alarms. People who warm their cars up in the garage are trapping CO inside the garage. The CO can find its way into the home.

    2. Gas cooking appliances.
    This is reported to account for 20% of CO alarms. It may be a result of a misused, poorly maintained, poorly installed, or unvented cooking appliance.

    3. Poor draft/venting for fuel burning appliances.
    This is one of the most common and serious causes for CO build-up and has been reported to account for up to 19% of CO alarms. The products of combustion are not being safely expelled to the exterior. This could be due to venting problems, such as blocked chimney flues or inadequate venting for appliances or fireplaces. Other problems include poor installation and negative air pressure in the house, causing backdrafting, often due to exhaust fans.

    Other problems include poor combustion at furnace. Inadequate combustion air to the furnace can result in incomplete combustion. If the furnace has a cracked heat exchanger, it is possible to get CO into the circulating air. It is also imperative that we do not deprive our heating equipment and fuel burning appliances of air; especially in air-tight homes where running exhaust fans can result in a shortage of combustion air. Combustion air is essential for safe operation of furnaces, water heaters, and other fuel burning equipment.

    There can also be a leak in a chimney or flue pipe.

    Ventilation issues are very common as a result of barbecues or gasoline powered equipment operating in an attached garage, basement, or enclosed area.

    Are there more problems with carbon monoxide today than 30 years ago?
    Yes, this is due to:

    • More energy-efficient, air-tight homes
    • Less natural ventilation

    How can I guard against carbon monoxide poisoning?

    The first line of defense is to have your home heating systems, fuel burning appliances, flues and chimneys checked and/or cleaned annually.

    Here is the inspection checklist. Specialists should check for:

    • Blocked openings to flues and chimneys
    • Cracked, rusted, or disconnected flue pipes
    • Dirty filters
    • Rusted or cracked heat exchanger
    • Soot or creosote build-up inside fireplaces and chimney flues
    • Exhaust or gas odors
    • Attached garages require gas proofing and automatic closers for doors into the home
    • Adequate combustion air
    • Adequate venting on indoor combustion appliances (i.e-gas stoves)

    The second line of defense is a CO detector.

    Carbon Monoxide Detectors


    It’s a relatively new technology introduced in the early 1990s. It is designed to warn homeowners when CO reaches dangerous levels within the home.

    How do they work?

    CO detectors sample the air at specific time intervals. A microchip inside the detector stores the reading and keeps track of the level of CO that the detector is exposed to over time

    Types of sensors:


    • Biometric (Oldest type of sensor)
    • Metal Oxide Semi-conductor
    • Electrochemical (The best of the three types for a residential sensor)


    • Infrared – Highly advanced, very expensive. Not something you would find at a typical hardware store.

    The detectors are supposed to sound an alarm when exposed to a set level of CO (measured in parts per million) over a specific time period. These levels or standards are set by UL (Underwriters Laboratories).

    Old Standard (Units manufactured between October 1, 1995 and October 1, 1998) - First Generation CO detectors.


    CO (ppm)


    To a low level for a prolonged period of time


    Alarm after 30 days

    To a low level of CO for an extended period of time


    Alarm within 90 minutes

    To a moderate level of CO for a shorter period of time


    Alarm within 35 minutes

    To a high level of CO for a short period of time


    Alarm within 15 minutes

    The UL Standard was revised and any detector manufactured after October 1, 1998 must conform to the new Standard.


    CO (ppm)


    To a low level for a prolonged period of time


    Alarm after 30 days

    To a low level of CO for an extended period of time


    Alarm within 189 minutes

    To a moderate level of CO for a shorter period of time


    Alarm within 50 minutes

    To a high level of CO for a short period of time


    Alarm within 15 minutes

    Also included in the new Standard is:

    • CO detector should ignore a CO level reading of 70 for at least 1 hour without alarming
    • CO detector should ignore a CO level reading of 150 for at least 10 minutes without alarming
    • Must only signal under alarm or trouble. No low-level warning signal is allowed
    • Must have a SILENCE button to shut it off. Must re-alarm after 6 minutes if CO levels persist
    • Must meet the specificity test referencing non-alarm status at specific concentrations of certain gases and vapors

    To put levels into perspective:

    CO Level (ppm)

    Health Effect


    Desirable level


    Maximum outdoor air quality level as per EPA


    Maximum concentration for a continuous exposure in an 8-hour time period (OSHA standard)


    Headaches in 1 to 2 hours, life threatening after 3 hours


    Nausea and convulsions, death within 2 hours


    Nausea within 20 minutes, death within 1 hour


    Death within 1 to 3 minutes

    Note: These studies are generally done on young, healthy people. These symptoms can change drastically depending on age, sex, weight, habits (e.g. smoking), and most importantly, your health.

    The Controversy

    • Reliability of the detectors

    The Issue

    • CO detectors are supposed to alarm at certain levels as indicated in the tables above
    • Recent testing suggests that many of these devices are not nearly as reliable as they should be
    • There has been regular television coverage that focused on false alarms and the reliability of CO detectors


    • In 1994, Chicago was the first major city to make these detectors mandatory in the living space
    • In the last three months of 1994, the Chicago Fire Department responded to 8,600 CO alarms
    • In almost every case there was no dangerous level of CO found during follow-up investigations


    • Laboratory testing was done
    • Up to 1/3 of the alarms tested, failed to alarm


    1. Technology

    • Technology for residential CO detectors is very primitive.
    • Industrial detectors have a different set of standards and more sophisticated technology. As a result, they are very expensive.
    • Different detectors have large variances on the levels at which they are supposed to alarm. The sensor technology used in home alarms is not designed to measure and display low level, short term concentrations of CO. Substantial differences exist in the sensitivity of different sensors at low levels. As a result, they may go off too soon or not soon enough.

    2. Humidity

    • Standards require these devices to be tested at a humidity of 50%.
    • Testing revealed that many devices failed to respond when humidity levels were low even though they are supposed to work within a large humidity range. See your CO detectors manual.
    • In colder climates, humidity levels can fall well below 50% (in fact the humidity should not be higher than 40%) during the cold season when furnaces and other fuel burning appliances are in full operation.

    3. Effect of Other Gases and Vapors

    • Other gases such as Carbon Dioxide can also trigger a CO alarm. The UL 2034 Standard requires that CO alarms do not alarm when certain concentrations of other gases and vapors exist in the vicinity of a CO detector. The level for Carbon Dioxide in the old standard was low, which may have contributed to many false alarms with first generation CO detectors.


    • CO detectors are designed to protect the average healthy human from death or serious injury under the current standards; however –
    • People who are more susceptible cannot depend on these devices for total protection. In this case, more sensitive CO detecting equipment should be used.
    • Several groups are working with UL to improve the standards. October 1999 revisions have already been drafted.
    • There is room for improvement by imposing stricter standards as well as technological development.
    • It is critical that people understand the dangers of CO and that the people who investigate it are properly trained and are using CO testing equipment properly.

    Where to install a CO detector?

    • One or more CO detectors in accordance with the manufacturer’s recommendations. Usually one per floor.
    • Maintain and test regularly as instructed by the manufacturer.

    Things to look for when buying a CO detector?

    1. Type of sensor (electrochemical)
    2. Certification-UL 2034
    3. Conforms to new standard
    4. IAS 6-96 is a supplementary standard to the UL 2034 which includes reliability testing. This standard may not be visible on the box.
    5. Other considerations include digital display, sensor life, power source, and warranty.

    How does all of this relate to your home inspection?

    A home inspection may reveal a potential Carbon Monoxide source.
    Common deficiencies found during inspections include:

    • Venting deficiencies
    • Damaged or rusted flue pipes
    • Dirty or blocked chimney flues
    • Cracked heat exchangers
    • Gas proofing deficiencies
    • Inadequate combustion air
    • Poorly installed equipment

    Limitations –

    • Visual Inspection
    • Equipment available

    There are other ways to test CO levels in a home. These tests go beyond the scope of a standard home inspection.

    Line drawings are from the Carson Dunlop Home Inspection Training Program and Home Inspection Software Tool – Horizon

  • Priority Maintenance for Home Buyers

    There are so many home maintenance and repair items that are important; it can be confusing trying to establish which are the most critical. To simplify things, we have compiled a short list of our favorites. These are by no means all-inclusive, nor do they replace any of the information in a home inspection report. They should, however, help you get started on the right foot. Remember, any items marked as priority or safety issues on your home inspection report need immediate attention.

    One-Time Tasks

    1. Install smoke detectors and carbon monoxide detectors as required, according to manufacturer’s recommendations. Know the requirements in your area.
    2. Make any electrical improvements recommended in the home inspection report.
    3. Remove any wood/soil contact to prevent rot and insect damage.
    4. Change the locks on all doors. Use a dead bolt for better security and to minimize insurance costs.
    5. Correct trip hazards such as broken or uneven walks and driveways, loose or torn carpet or uneven flooring.
    6. Correct unsafe stairways and landings. (Railings missing, loose, too low, et cetera.)
    7. Have all chimneys inspected before operating any of these appliances.
    8. Locate and mark the shut-offs for the heating, electrical and plumbing systems.
    9. Label the circuits in electrical panels.
    10. If there is a septic system, have the tank pumped and inspected. If the house is on a private water supply (well), set up a regular testing procedure for checking water quality.

    Regular Maintenance Items

    1. Clean the gutters in the spring and fall.
    2. Check for damaged roofing and flashing materials twice a year.
    3. Cut back trees and shrubs from the house walls, roof and air conditioning system as needed.
    4. Clean the tracks on horizontal sliding windows annually, and ensure the drain holes are clear.
    5. Test ground fault circuit interrupters, carbon monoxide detectors and smoke detectors using the test button, monthly.
    6. Service furnace or boiler yearly.
    7. Check furnace filters, humidifiers and electronic air cleaners monthly.
    8. Check the bathtub and shower caulking monthly and improve promptly as needed.
    9. If you are in a climate where freezing occurs, shut off outdoor water faucets in the fall.
    10. Check reversing mechanism on garage door opener monthly.
    11. Check attics for evidence of leaks and condensation and make sure vents are not obstructed, at least twice a year. (Provide access into all attics and crawl spaces.)

    Line drawings are from the Carson Dunlop Home Inspection Training Program and Home Inspection Software Tool – Horizon

  • Your New Home: Kick the Bricks!

    As a professional house and building inspection company, one of our primary jobs is answering questions. One of the most common questions we get is "Should I have my brand new house inspected?" It's a fair and honest question. The short answer is YES. But you expected us to say that, right? Let me tell you why it's a fair and honest answer.

    Risk Reduction

    Let's take the emotion out of it. Let's not call it your home; let's say it's a house. A building with a roof, a structure, mechanical systems, and interior finishes. It requires a substantial investment for you to purchase this building. You are putting your money at risk. It makes sense for you to learn about the qualities of this investment before putting your money on the line.

    "But what could be wrong? It's a new house?" Yes, the risk of problems is probably lower than if you bought an old building. It actually depends on the individual properties one is comparing. It boils down to illuminating the risk, rather than assuming there is none.

    House vs. Home

    But it is artificial to take emotion out of it, precisely because the building will be your home. So you have a financial and an emotional investment. Why is this important? Because even a small problem, like for example a leak at the kitchen sink, will elicit in you an emotional response. What happens when you notice the leak? You get an adrenaline rush, you turn off the tap or the dishwasher, you wipe up the water, you remove the soaking box of dishwasher detergent, you wonder what you should do next, you call someone you trust, you call the builder or a plumber, you wait to make dinner until the service-person arrives. A non-trivial emotional investment, for a minor problem.

    For some people, that minor incident will bring on a not-so-minor bout of buyer's remorse, wherein they wonder, "What else will go wrong?" It is better for both you and your builder for the inspector to find the leak so it can be fixed immediately.

    Helps the Builder

    Your builder has worked hard to put your home together. It takes a phenomenal amount of coordination to turn an empty patch of ground into a dream house. With so many steps and so many hands, it is inevitable that some things will get missed. Sometimes we find electrical outlets that don't work. Sometimes we find un-insulated attics. These were not done on purpose, they just happen. If you hire an inspector to find the things that need attention, you can put the items on the PDI punch-list (the list of deficiencies generated at the pre-delivery inspection that the builder is contracted to fix), or you will have documentation of the issues and can bring them up later. This helps both you and the builder keep track of the final wrinkles to be ironed out. If there are only a few wrinkles, you will gain an appreciation of how well the house has been built.

    11-month Inspection

    Many of our clients choose to hire us after they move in, but before the standard one-year builder's warranty coverage expires. This has proven to be a uniquely successful strategy. The waiting period allows the newly built house to "settle-in", making a performance-based inspection more valuable.

    No matter how you look at it, getting a professional building inspector to kick the bricks of your new home is a sound idea.

    As seen in HOMES Magazine June/July/August 2003. Gerard Gransaull, P. Eng., Engineering Manager, Carson Dunlop and Associates Ltd., Consulting Engineers - Building Inspections, www.carsondunlop.com

    Line drawings are from the Carson Dunlop Home Inspection Training Program and Home Inspection Software Tool – Horizon

  • Undertaking A Home Repair

    Let's start by differentiating between a home improvement and a home repair. A home improvement, as the name implies, means improving something. It is usually a renovation to create more space, changing the layout of the house, improving energy efficiency, or to making aesthetic changes.
    This report will deal with the simpler topic of home repair – basically replacing things that are worn out or fixing things that are broken. Here are some very basic rules to follow.

    1. Know what you want done

    If you are replacing a worn out furnace, for example, do some research to find out whether you want a mid-efficiency furnace or a high-efficiency furnace. If you are repairing a roof with a leaking valley flashing, determine whether you want the valley flashing replaced or just patched to last a few years until the whole roof needs re-flashing.

    If you know what you want done, you can compare apples to apples when reviewing quotations. Otherwise it would be very hard to compare various quotes if every contractor has a different repair strategy.

    Be prepared to stick to your guns. Many contractors will tell you that the job is much bigger, much harder, or it must be done his way (because if you don't, it will be “dangerous”, or much more expensive the next time.)

    As home inspectors, we are often faced with contractor opinions that differ drastically from the recommendations in our reports. In many of these cases, the contractor is proposing unnecessary work.

    2. Find at least 3 experienced, reputable contractors who are capable of doing the work

    This may sound easier than it is. While it is best to rely on personal referrals from people you trust, these referrals must be taken with a grain of salt. Former customers of contractors are not usually in a position to comment on the quality of the installation of a furnace, for example.

    Also be sure the type of work that you are planning to have done is similar (in size and scope) to the work done for the person providing the referral. Many contractors who are geared to do major renovations are not well suited to do minor repairs and vice versa.

    3. Obtain 3 written estimates

    Our experience has shown that contractor quotes can vary as much as 300% on any given job. This is sometimes due to different perceptions of what needs to be done. This can be avoided by following Step 1 carefully. However, sometimes the variance is simply the result of how busy the contractor is.

    4. Get three references from each contractor

    Better than three references is a list of the recent clients that the contractor has worked for. That way you get to choose who you would like to select as a reference. Follow up with these references bearing in mind the comments in Step 2.

    While you are at it, ensure that the contractor has appropriate licenses and insurance.

    5. Choose the contractor

    Don't necessarily base your choice on price alone. Look carefully at what has been included in the estimates. Select the contractor with the best reputation, provided that the price for the job is fair. Avoid paying cash. The benefit of a cash deal is typically far greater for the contractor than it is for the homeowner.

    6. Have both parties sign a contract

    The contract should include a complete description of the work. It should also include details as to who is responsible for obtaining permits (if there is any doubt regarding the necessity of a permit, contact your local building department).

    The contract should have a start date and a completion date. (On larger contracts, sometimes a penalty clause is included for each day the job extends beyond the completion date.)

    The contract must also contain a payment schedule. The schedule should not demand very much money up front and the payment should be based on stages of completion as opposed to pre-determined dates.

    Remember to hold back 10% of each payment for 45 days after the completion of the job to determine whether any liens have been placed on the property (as a result of the contractor not paying his sub-contractors).

    Also, don't expect much in the way of a guarantee if you are simply asking a contractor to undertake band-aid repairs. Many contractors will not simply patch a damaged valley flashing, for example, even if they are 95% sure that the repair will work. This is because there is still a 5% chance that they will get complaints to fix a subsequent leak. In fairness, the leakage is not their fault. They just do not want the hassles. Consequently, many contractors will suggest repairs which are unnecessary (replacing the entire side of the roof, for example) to reduce the potential for complaints.

    A significantly lower price can be obtained if you explain to the contractor that you expect him to do his best, but you aren't going to make him responsible for the future of the entire roof based on a $300 repair.

    7. Expect delays

    Any type of home repair seems to take longer than was first predicted. If the repairs involve any sort of interior demolition, expect dust.

    8. Have a contingency fund

    Many home repairs end up unearthing something else that requires repair. While this is very common, ask lots of questions if your contractor is proposing additional work.


    We trust that the above information will help people in their dealings with contractors, realign expectations, and perhaps avoid pitfalls.

    Line drawings are from the Carson Dunlop Home Inspection Training Program and Home Inspection Software Tool – Horizon