Tripped Rollout Switch

Anytime you have to reset a rollout switch on a furnace, warning alarms should go off in your head. The switch is not the problem, it is a symptom of a very serious problem. Just resetting the switch and going on is like turning off a fire alarm and leaving the fire burning. You need to find out why the rollout tripped. Rollout switches trip because flames are burning back where they are not supposed to be. Possible causes include a stopped up vent, a stopped up heat exchanger, low gas pressure, or a cracked heat exchanger. All of these conditions are very serious and have the potential to do great harm. Figure 1 shows a common rollout switch.

Figure 1 Rollout Switch

In the case of the plugged vent or heat exchanger. The flue gas cannot exit quickly enough, builds up and pushes the flames out of the heat exchanger into the area where normally there is only secondary combustion air. Although 80% gas furnace heat exchangers seldom become restricted, the condensing, secondary heat exchangers on 90% furnaces often become restricted. Either way, you must have a clear heat exchanger and vent to operate the furnace safely.

A cracked heat exchanger  can also lead to tripped rollout switches. A cracked heat exchanger can allow positive pressure air from the blower into the heat exchanger and reduce the draft. If the hole is big enough, the pressure in that cell of the heat exchanger can become positive, and push the flames out of the heat exchanger into the area where normally there is only secondary combustion air. Figure 2 shows an example of this. Look carefully at the burner on the left. See that there is no bright inner cone. That is because the flames are coming back out of the tube. The burner to the right of it looks normal.

Figure 2 Flames rolling out (left burner)

Low gas pressure can cause the flame to retreat from the burner port, back into the burner body, often all the way to the orifice. Figure 3 shows an example of flames burning back at the orifice due to low gas pressure.

Figure 3 Flames burning back at orifice

Whenever you find a furnace with a tripped rollout switch, you need to determine why the rollout switch has tripped. I know no professional would ever jump out a safety device, such as a rollout switch. But just to make certain – NEVER “fix” a furnace by jumping out a rollout switch. The switch is not the problem – it may be the reason nobody died.

CSST Gas Lines

If you use flexible gas connectors or CSST (corrugated stainless steel tubing) when hooking up the gas to a gas appliance, you need to make sure and do it safely. Flexible gas connectors are made of corrugated stainless steel and generally have no outer covering or protection. They are often used to connect a gas appliance to a rigid iron gas line. 

CSST, on the other hand, has an outer covering over the corrugated stainless steel, comes in large rolls, and is often used instead of black iron when piping gas lines. There are some installation practices for each of these products that need to be followed to avoid setting up a dangerous situation.

For flexible connectors, it is important that they not be used to go through walls, floors, or the unit cabinet. Iron pipe should pass through the unit cabinet to the gas valve. Contact with the metal side of the furnace cabinet can rub a hole in a flexible connector. Another reason for keeping flexible connectors out of the cabinet is the potential for loose electrical wires or connections to arc against the flexible connector and blow a hole in it. While this could also happen with black iron, there is far less likelihood of the arc blasting a hole in the iron. 

Flexible connectors can be used to make the final connection between the black iron leaving the furnace cabinet and the black iron piped into the furnace area. When using a flexible connector, the flared connectors are generally considered “unions.” Don’t forget to install a gas shutoff. Some flexible connectors are provided with a gas shutoff.

CSST is similar to flex connectors in construction with an outer layer of protective plastic. CSST can be pulled through interior walls, but metal nail protectors are required anywhere the CSST is inside the wall. CSST manufacturers make striker plates for this purpose. Protection needs to be approved by a listing agency, such as CSA or UL. Also, it is still best to use black iron to go into the furnace cabinet. The best practice is to penetrate exterior walls with black iron. If CSST is used to penetrate an exterior wall, protection is required.

One of the biggest safety concerns with both flexible connectors and CSST piping is properly grounding the gas piping system. There have been many instances where lightning strikes near a building have blown holes in CSST gas lines or connectors. The grounding is to avoid this. The most common practice is to connect a bonding ground wire to the rigid black iron pipe outside the house BEFORE the first CSST connection. This bonding ground is connected to the ground rod or run inside to the ground bus of the electrical panel.

Here are a couple of links for more information”

Grounding: http://www.csstsafety.com/CSST-solution.html

Installation: http://www.tracpipe.com/Technical/CSST_Installation_Instructions/  

Check Combustion Air

With the weather getting cooler, I thought that now would be a good time to talk about combustion air. Don’t forget to check for proper combustion air. Most codes provide detailed drawings illustrating where combustion air should come from and how much you need, but there are still many furnace installations that rely entirely on air from inside the building for combustion air. In days gone by this was often considered adequate so long as the furnace was located in a large enough space. In newer homes, combustion air should always be provided.

Most 90%  furnaces today can operate using sealed combustion. In the case of a sealed combustion furnace, the combustion air is being piped in from the outside. The combustion air is piped directly into the furnace. These are easy to spot, they have two pipes: one for combustion air and one for the vent. Also, their panels have no louvers for combustion air. 

Traditional furnaces get their combustion air from the space where they are installed. Combustion air enters through louvers in their panels.Since the furnace is drawing air from the space it is in, fresh combustion air must be supplied to the room to keep the process going. Failure to supply the correct amount of combustion air can lead to negative room pressure, vent spillage, poor combustion, and CO production. All these things together can be disastrous.

When a technician checks a furnace that does not have sealed combustion, one of the first things to look for is how the furnace receives combustion air. If the furnace is in a ventilated crawlspace or attic, the ventilation for those spaces provides the combustion air. However, even these can be a problem. A large furnace in a small crawl space may not have adequate combustion air if the crawl space vents are closed. I have also seen crawlspace vents clogged with debris, effectively reducing the combustion air.  

The most troublesome installations are furnaces located inside the house in a closet. They should have a combustion air vent near the floor and another near the ceiling. Someone asked me about a furnace installed in a closet off of a bathroom. When they turn on the bathroom vent fan, they can smell gas! Another story involved a fireplace and a furnace. When the furnace came on it sucked the smoke out of the fireplace into the room. These types of stories indicate that the furnace does not have adequate combustion air. 

What if there are no obvious combustion air vents? Sometimes the vents were never provided, other times they have been covered up. I have seen combustion air vents covered with tape or plastic. Undoubtedly, someone noticed cold air coming in the vent and “fixed” the problem – thereby creating a combustion air problem. Occasionally insulation covers the grille into the attic. Another problem is using the furnace closet for storage. This is dangerous in and of itself, but it can also cause combustion air problems if boxes are stacked in front of the combustion air grilles.  For details on combustion air requirements check your local code. Unit 53 Gas Furnace Installation in Fundamentals of HVACR, 3rd ed also has detailed drawings and specifications for the most common applications.  

Residential Combustion Analyzers

To measure combustion efficiency you need a tool that can measure either the oxygen or CO2 content of the combustion gasses. For many years, an hour glass shaped bubbler containing a fluid that absorbs CO2 or O2 was used. They are difficult to find these days. They have been replaced by electronic instruments. These use an electro-chemical reaction in an oxygen sensor to measure the O2 content in the flue gases. They use thermistors to read the flue gas temperature and ambient temperature, so they have all the information that need to calculate and display combustion efficiency. They use this information to display CO2 %, O2 %, combustion efficiency, % excess air, flue gas temperature, and net stack temperature. Most offer other measurements as well. Some of the more common additional features include:

• CO ppm – to read the CO in the flue gas

• CO ppm air free – to calculate the CO ppm after removing the excess air

• Draft pressure – to insure you actually have a draft

• Differential draft pressure – to insure the draft pressure is lower than the room pressure

• NOX – to comply with NOX regulations in areas that restrict furnace NOX emissions

• Printer – to print out reports from results

• Computer Connectivity – to import data from analyzer to programs on your computer

Prices vary a good bit. From just over $500 for no-frills analyzers intended for residential work, to several thousand for commercial instruments. Certificates of NIST traceability often cost more.  Most combustion analyzers use electro-chemical sensors. These have a limited life because the chemicals in them are used up as they work. Typical replacement time is every one to two years. Some are user replaceable, and others require sending in the tool for the sensors to be replaced. This will typically cost $200 - $300. The table below compares several of the lower priced models which are aimed at the residential market.

	Bacharach Intech	Testo 310	UEI C75	E Instruments BTU 900
O2	yes	yes	yes	yes
CO2	yes	yes	yes	yes
Efficiency	yes	yes	yes	yes
Excess Air	yes	yes	yes	yes
CO	yes	yes	yes	yes
Air Free CO	yes	yes	no	yes
Draft pressure	no	yes	no	yes
Differential Pressure	no	no	no	yes
NOX	no	no	no	Can upgrade
Printer	Available Extra Cost	Available Extra Cost	Available Extra Cost	Available Extra Cost
Computer Connectivity	no	no	No	USB & Bluetooth
Field replaceable sensor	yes	no	no	yes
Fuels	6	5	5	10
Warranty	2 years	2 years	3 years	2 year
Approximate Street Price	$520	$600	$500	$1000

Combustion Efficiency

Fall tune up season is here. A seasonal check on a gas or oil furnace should include a check of the combustion process. To do a good job you really need to measure the combustion efficiency. To measure combustion efficiency you need to take two temperature readings and one flue gas reading.  The temperatures are the flue gas temperature and the ambient temperature around the unit. You subtract the ambient temperature from the flue gas temperature to get what is called the net stack temperature. The flue gas reading can be either CO2 or O2.Generally oxygen is preferred. For a gas furnace, perfect stoichiometric combustion produces 12% CO2 in the flue gas. The CO2 percentage drops off if the process is either too rich (too much fuel) or too lean (too much air). At the perfect stoichiometric point the O2 will still be 0% because all of it is being used in the combustion process. As excess air is introduced into the process, the O2 begins to rise due to the oxygen content in the air that was not used in the combustion process. Excess air is introduced to insure complete combustion. Note that complete combustion is not the same as perfect combustion. In perfect (stoichiometric) combustion, ALL the fuel and ALL the oxygen are used up, producing ONLY carbon dioxide and water. In complete combustion, all the fuel is used up, but not necessarily all the oxygen. Lack of combustion air produces incomplete combustion. Incomplete combustion leaves some unburned carbon and carbon monoxide. Excess air is introduced on purpose to prevent the production of soot and CO in the flue gas. The figure below shows the relationship of CO2, CO, O2 , and excess air. Next week we will discuss some of the ore practical aspects of measuring the combustion process.

Why Excess Air Is Important

Combustion requires oxygen, which furnaces get from the air. Ventilation of the combustion products from a draft hood appliance, such as a water heater or an older natural draft furnace, requires even more air. For theoretically perfect combustion you need 10 cubic feet of air for every cubic foot of natural gas that is burned. However, the burners in even the most modern and well designed furnaces are not perfect. Combustion appliances all introduce excess air to insure there is enough oxygen for safe combustion. Too little excess air will have the burners operating in an oxygen starved condition, creating high levels of carbon monoxide (CO). Too much excess air can also be bad. Too much excess air will cool the flame, and also produce high levels of CO. Typical older natural draft appliances with atmospheric burners use around 50% excess air, turning the 10 CF of combustion air to 15 cubic feet. Nearly all residential furnaces manufactured today are induced draft appliances with atmospheric burners. In these furnaces, the excess air is more typically 20% - 40%. Excess air can safely go as low as 10% for commercial power burners that do a better job of mixing the air and gas.

In general, excess air decreases efficiency by cooling the combustion process. For any furnace, the ideal amount of excess air would produce the highest combustion efficiency without introducing an excessive level of CO in the flue gas. In most cases, as you reduce excess air you will see both the efficiency and CO increase. If the amount of excess air is excessive, reducing the excess air may actually decrease the CO produced in the flue gas. You want to keep the air-free CO below 400 ppm, the ANSI standard. Many techs try to keep the air-free below 100 ppm. Older gas furnaces had primary air adjustments, making it possible to adjust the amount of air being mixed with the gas. Newer furnaces do not have any air adjustments. You can only adjust the amount of fuel by adjusting the manifold pressure or orifice size. Increasing the gas being burned has the effect of reducing the excess air because now more air is needed. However, you should NOT overfire the furnace in an attempt to improve efficiency. When making any adjustments to manifold pressure or orifice size, always check orifice sizes and manifold pressure against the manufacturers specifications and the heat content of the gas supplied by the local gas utility. To read more on how combustion efficiency and CO production are affected by excess air, check out the Combustion Guide from Tru-Tech Tools (it is a free download HERE).

Gas Furnace Firing Rate

How do you know the rate at which your furnace is actually firing? You really can’t assume that it is firing at the manufacturer’s published rate just because the manifold pressure is at 3.5”, even if that is what is specified on the nameplate. To determine the Btuh firing rate of your furnace you must first determine the cubic feet of gas per hour being burned (CFH) and multiply that times the heat content of the gas. To determine the CFH, you need to clock the gas meter. First, you want to turn off all other gas appliances. Then clock the number of seconds it takes for the smallest dial on the gas meter to make one revolution. For more accurate results, clock the time for two or three revolutions. The CFH can be calculated by dividing the time clocked into 3600 (the number of seconds in an hour). Multiply this answer times the value of the dial. If you clocked for multiple revolutions, multiply by the number of revolutions. The formula looks something like this

(3600/time clocked) x dial value x revolutions = CFH
So if the a 1/2 ft3 dial took 90 seconds to make three revolutions
(3600/90) x 1/2 x 3 = 40 x 1/2 x 3 = 60 CFH

Next, you need to know the heat value of your gas. You get this from your local gas supplier. If you can’t get that you can get a good estimate from the EIA. The US Energy Information Administration (EIA) has a table online that shows historical values for every state. GAS HEATING VALUES.

In our example, if the furnace is in Mississippi in 2011, the gas heat content is somewhere around 1010 Btu/ft3. So our firing rate would be 60 ft3/hr x 1010 BTU/ft3 = 60,600 BTU/hr

The same results in West Virginia in 2011 would mean a firing rate of 60 ft3/hr x 1083 BTU/ft3 = 64,980 BTU/hr

If the furnace in West Virginia is rated for 60,000 Btuh, you would need to reduce the manifold pressure slightly to reduce the firing rate. Another complication is altitude. Furnaces need to be de-rated approximately 4% for every 1,000 ft of altitude. In West Virginia, it is quite possible to be 3,000 ft above sea level, necessitating a 12% reduction in firing rate. So the new firing rate should be 60,000 Btuh x 88% = 52,800 Btuh. Now you are looking at firing a furnace at 64,980 Btuh which should only be fired at 52,800 Btuh. You most likely will need to change orifices as well as adjust the manifold pressure. After making any changes to the manifold pressure or orifices, make certain to clock the meter again and recalculate the gas firing rate to insure your adjustments brought the firing rate into line. Over firing a furnace can increase the production of CO in the flue gas. In extreme examples, it can cause soot formation.  

Natural Gas Furnace Firing Rate

Do you know the heat content of the natural gas supplied to your area? Although we often use the nominal value of 1000 Btuh per cubic foot for natural gas, the heating value is really a bit higher in most places. A look at a table by the U.S. Energy Information Administration, EIA, shows that only a few states have natural gas with a heating value close to 1000.Gas Heating Values In 2011, average gas heating values ranged from 1004 in Nebraska to 1076 in West Virginia. Furnace manufacturers must choose a heating value when they select the orifices to put in the furnace. Typically, they use a value on the higher end of the range, 1075 BTUs/ft3. A furnace with the factory supplied orifices set up at the same manifold pressure in each of these states would deliver a different amount of heat. Assuming they were all installed at sea level in their respective states, they would burn the same volume of gas because they would have the same manifold pressure and the same orifice size. A furnace that burns 100,000 Btuh in West Virginia would only be firing at 93,000 Btuh in Nebraska. Small adjustments in the firing rate can be made by adjusting the manifold pressure. However, it is often necessary to change the burner orifices to get the manufacturer’s listed firing rate.

Higher altitudes can make de-rating a furnace necessary because the lower pressure, less dense air just does not have enough oxygen in it to support the full capacity of the unit. In general, furnaces are de-rated 4% for each 1,000 ft of altitude. Some manufacturers provide tables showing what orifices and manifold pressure should be used depending upon the gas heating value and altitude. The point is that setting up a furnace for the correct firing rate involves a little more than simply adjusting the manifold pressure to 3.5" wc using the manufacturer supplied orifices. You may need to change the orifices and/or adjust the manifold pressure to something other than 3.5" wc. Below is an example from one manufacturer. Note that this is an example - it does NOT apply to all furnaces.

Gas Heating Value	Sea level - 2000		2001 - 3000		3001 - 4000		4001 - 5000
	Orifice	Man press	Orifice	Man press	Orifice	Man press	Orifice	Man press
975	44	3.3” wc	44	2.8” wc	44	2.6” wc	47	3.5” wc
1000	44	3.2” wc	44	2.7” wc	44	2.5” wc	47	3.3” wc
1050	44	2.9” wc	44	2.5” wc	48	3.7” wc	48	3.4” wc
1100	46	3.3” wc	48	3.7” wc	48	3.4” wc	48	3.7” wc

Checking Gas Pressure

Heating season is upon us and it is time to get out your gas pressure measuring instruments. What do you use to check gas pressure on natural gas furnaces? A popular tool that I see a lot is probably the least accurate available. Many techs use the diaphragm gauge gas pressure test kit which comes in the blue plastic box. But these can’t read anything below 2” wc, making them useless for the low fire stage of a two stage furnace. Even 3.5” is in the first part of the scale, not in the sweet spot. If you are testing natural gas and feel that you must use one of the diaphragm pressure gauge gas test kits, at least get the model that puts 3.5” wc more towards the center of the scale. Then you can actually read a pressure of 1” wc. The reason many people don’t choose the gauge which is more appropriate for natural gas is that it does not read high enough for propane. So they buy the gauge that was really designed to read propane gas pressure and use it for both. That sounds reasonable, until you try to read gas pressure on a two stage natural gas furnace using one of those gauges and cannot get a reading.

For an inexpensive gas manometer, an actual water column manometer is a far better choice. I like the straight tube water manometers that Yellow Jacket sells. They are actually cheaper than their gauge style gas pressure test kits and more accurate. No, they are not quite as easy to use – you have to put water in them and learn to read the bubble in the center tube, but that is not too difficult. For a little more money you can buy a U-tube manometer. If you want both convenience and accuracy, a digital manometer is the thing to get. They are considerably more expensive, but also considerably more accurate and convenient. An added bonus is that you can also use most digital manometers to read duct pressures – so the tool can serve more than one function.

Why should you worry about how accurately your manometer reads the gas pressure? Because you cannot insure the furnace is operating safely at the correct firing rate and efficiency if you don’t really know what the manifold pressure is. Checking furnace operation by just seeing blue flames is similar to checking the charge of an air conditioning system by just feeling to see that the suction line is cold. You can see that it is operating, but you really don’t know it is operating as designed. Incorrect gas manifold pressure can lower system operating efficiency and increase the operating cost. Under fired furnaces will lose capacity, over-fired furnaces can be a safety risk due to increased CO output. So do yourself and your customers a favor and get a tool that will allow you to take an accurate manifold pressure, even on low fire.

PVC Vents for Condensing Furnaces

Since the advent of condensing furnaces, furnace manufacturers have been specifying  Schedule 40 PVC as the venting material they recommend. A good discussion of condensing furnace venting by Bob Formisano can be found at the HomeRepair site. Traditional metal vent material generally will not work because the vent gas on a 90%+ furnace is very wet and at a positive pressure. Other than stainless steel, metal vents would not last very long. Because the vent operates at a positive pressure, it must be sealed air tight. Traditional Type B vents are not air tight. With a negative pressure vent, the very small leaks in type B vents do not pose any problem. But if they were carrying pressurized vent gasses, even small leaks are a safety hazard. Since the flue gas temperature of a condensing furnace is much lower than a traditional furnace, plastic materials are feasible. So PVC seems like a good choice. It is definitely water proof and sealing it air tight is quite easy. The fact that PVC is inexpensive also makes it attractive. However, the standard referenced by many furnace manufacturers, ASTM D1785 for Schedule 40 PVC pipe, does not actually test PVC piping as a flue material. In fact, it specifically states that the standard does NOT cover its use as a vent for combustion appliances.

There have been concerns about PVC vent systems failing. Two sites I found that discuss failures and show pictures are  HeatingHelp, and Plumbing Engineering  Both sites discuss PVC venting systems on condensing water heaters and boilers where the PVC material turned brown, became brittle, and cracked or broke. In Canada, plastic vent materials must conform to ULC 636 – meaning no more “standard” PVC venting. It appears we may follow in the US. Some plastic materials made specifically for venting include UL 636 PVC, UL 636 CPVC, and a special polypropyylene pipe.

Here are a few links.
UL 636 PVC, CPVC
Polypropylene

Check the Draft

With the arrival of Fall weather technicians will soon be taking Fall furnace checkup calls. One of the things we should be doing is checking the vent draft pressure to insure that the vent is working properly. While many technicians are careful to check for cracks in heat exchangers, they sometimes neglect the vent. I believe that improper venting occurs far more often than cracked heat exchangers. Further, a vent that is spilling into the house has the potential to release far more vent gasses into the house than a crack in the heat exchanger. Of course it is right to check for cracks in the heat exchanger, just don’t neglect the vent operation. For all Category I furnaces, the vent should be a negative pressure. That is, it should be at a lower pressure than the room the furnace is operating in. Typically we want at least -0.02” wc. In other words, the vent pressure should be 0.02”wc less than the room pressure. This is true even with fan assisted Category I furnaces, which nearly all 80% AFUE furnaces are today. The fan helps pull the combustion gasses through the heat exchanger, it is NOT designed to PUSH vent gasses through the vent. Typical Class B vent is not air tight. If it is pressurized, it will leak out combustion gas.Even with fan assisted furnaces, the vent is supposed to operate at a negative pressure and the vent gasses leave because of their buoyancy compared to the surrounding air.

What can cause a lack of draft in a vent? One of the main culprits is lack of combustion air. The operation of the burners and the vent system can remove air from the room faster than it is being supplied, causing a negative pressure in the room. In older, leakier homes we often relied on infiltration for combustion air. Today, you really should provide outside air to the appliances. I have seen the operation of a furnace pull smoke out of a burning fireplace. There was enough air for the fireplace, but not both the fireplace and the furnace. The room went so negative that the fireplace vent was not lower than the room pressure. If the vent gasses cool off too much in the vent pressure will increase because the gasses are heavier, decreasing the draft. This can be a particular problem when replacing an older furnace with a newer one. Often, the vent is too big for the new furnace, causing the flue gas to cool off too much as it travels through. Another possibility is a plugged vent or vent cap. The flue gasses back up in the vent and then start to spill out of the appliance. 

Although most Category I furnaces with draft inducer fans have draft pressure switches to shut off the burners if the draft pressure is not at the minimum setting for the switch, I have seen furnaces operating with a positive vent pressure continue to run. Draft switches are, after all, switches and can fail. So don’t assume that because the draft switch is closed, the vent pressure is OK – measure it so you know.

Sometimes HVAC/R technicians have an opportunity to do more than make people comfortable, we can save lives. More people are sickened or killed by carbon monoxide poisoning than any other type of poison. The Center for Disease Control and Prevention (CDC) reports that each year more than 500 people in the United States accidentally die from carbon monoxide. An estimated 10,000 people in the U.S. are treated for CO poisoning in hospital emergency rooms annually. It is believed that many more people suffering CO poisoning are misdiagnosed, or never seek medical care. This is because the symptoms of CO poisoning are very similar to influenza symptoms. One big difference is that influenza causes a fever and CO poisoning does not.

Carbon monoxide is an odorless, colorless gas that is highly poisonous. It is formed by the incomplete combustion of carbon based fuels, like natural gas, oil, coal, or wood. Incomplete combustion can be caused by lack of oxygen, improper mixing of the fuel and oxygen, or too low a combustion temperature. A correctly adjusted gas or fuel oil flame should produce very low levels of CO. Ideally a correctly adjusted gas or oil flame should produce no CO, but realistically, most produce at least trace amounts. Solid fuels almost always produce large amounts of CO, that is why charcoal comes with a warning that it is not to be used inside. Even people that should know better sometimes overlook the obvious. A friend of mine was conserving heat during a cold winter power outage by using his charcoal grill inside. His daughter became very ill and had to be rushed to the hospital where they correctly diagnosed her condition. This story ended well, she recovered and is doing well. Unfortunately there are many stories about CO that do not end well.

HVAC/R technicians are in a position to help. We can make sure all combustion appliances in the home are burning correctly, insure there is enough combustion air for proper combustion and venting, and finally by making sure the vent system is adequate and working correctly. For gas and oil furnaces also remember to inspect the heat exchanger for leaks. The heat exchanger separates the combustion products from the air circulating in the home. Although a defective or cracked heat exchanger can contribute to CO poisoning, more obvious problems are frequently to blame. Stopped vents, loose or leaky vents, and lack of combustion air are common causes of CO. While every technician should learn to look for conditions that can lead to problems, testing is required to verify that a system is operating at safe levels of CO and that there is no CO in the house. Every technician should have an accurate CO tester. Household alarms are not a substitute. While every house with gas or oil appliances certainly should have CO alarms, they are not a replacement for an accurate tool for diagnosis. I highly recommend a seminar done by Bob Dwyer for COSA (Carbon Monoxide Safety Organization) Make sure and take advantage of the opportunity if you have a chance to attend one of his CO Safety Seminars.

There are many units in Fundamentals of HVAC/R to help explain how to achieve safe, efficient combustion for gas and oil furnaces, including

• Unit 37 Gas Fired Heating Systems
• Unit 38 Warm Air Furnaces
• Unit 40 Gas Furnace Installation, Startup, Checkout, and Operation
• Unit 41 Troubleshooting Gas Furnaces
• Unit 42 Oil Fired Heating Systems
• Unit 43 Oil Furnace and Boiler Service
• Unit 44 Residential Oil Heating Installation
• Unit 45 Troubleshooting Oil Heating Systems

There are many good web sites for more research on carbon monoxide poisoning.

A few are listed below.

http://www.bbc.co.uk/health/conditions/carbonmonoxide1.shtml

http://www.cosafety.org/Aboutco.htm

http://www.clima-tex.com/consumer/carbonmonaction.html

http://annhyg.oxfordjournals.org/cgi/content/abstract/18/1/79

http://www.coheadquarters.com/colimits1.htm

http://www.coheadquarters.com/CarbonMonoxideHQ.com/index.html