What is Combustion Testing all about?
As most people are aware, a flame requires an ignition source, fuel and air to burn.
Heating systems commonly use a pilot light or spark to light the flame, then very specific amounts of fuel and air are required to keep it burning properly.
The air we breath and use for combustion consists of about 21% oxygen, the remaining 79% is nitrogen.
When we inhale air (at 21% oxygen) we only 'consume' somewhere between 5% to 7% and as a result, when we exhale, there is still about 14% to 16% of that oxygen remaining.
For example, you can breath in and out of a balloon several times before all the oxygen is used up and it becomes uncomfortable.
This is very similar to the combustion process in your heating system
During the combustion process, the flame burns oxygen from the air and converts it into usable heat. However, it is impossible for the flame to burn 100% of the oxygen in the combustion air supply.
All heating systems are designed and engineered to burn a very specific range of the oxygen in the combustion air depending on the type of fuel being burned and the design of the heating equipment.
Combustion test instruments measure the amount of oxygen remaining after the combustion process (in the flue gases) to verify that the heating appliance is operating as it intended.
For more technical information on the generally accepted flue gas oxygen levels, click here.
Heating systems are also designed to operate with a very specific range of flue gas or stack temperatures. Too high of a stack temperature commonly results in higher fuel bills, too low of a stack temperature may allow the moisture in flue gases to condense before the flue gases completely exhaust the vent system or chimney.
The moisture produced in the combustion process is very acidic and when it condenses on metal vent materials or masonry chimneys, it will corrode the vent or chimney.
For more technical information on chimney draft, click here.
An exception to this are the 90% or condensing furnaces and boilers. This type of equipment intentionally lowers the temperature of the flue gases to the point where it does condense and is able to put more heat into the home.
However, even the 90%, condensing equipment is still designed and engineered to operate within a very specific range of stack temperatures and the amount of oxygen remaining after the combustion process (in the flue gases).
Bacharach invented the first portable combustion analyzer in 1932, mostly for large industrial burners, specifically the steel mills in Pittsburgh where the Bacharach was, and still is, located.
This instrument gained wide use during WWII when they were commonly used on Navy ships to reduce the amount of fuel consumed and maximize the power the ships' boilers were able to produce. Two very important considerations on the battlefield.
As fuel costs begin to rise, it became more and more common for heating contractors to use this type of instrument on residential heating equipment as well.
Now, with the advent of inexpensive, sophisticated electronics, most contractors have upgraded to digital equipment as opposed to the old style mechanical instruments.
The primary disadvantage of the old style mechanical test instruments is that they took a 'snapshot' of the combustion process at one particular moment in the operation of the burner. The newer electronic instruments (which became commonly used in the early 1980's) allow the user to take a 'video' of the burner's operation throughout the entire cycle of operation - from start up to shut down.
More importantly, the electronic test instruments allow a contractor to measure and minimize the amount of Carbon Monoxide (CO) produced by the furnace, boiler or domestic hot water tank. Click here to learn more about CO.
MAKE ABSOLUTELY CERTAIN that the heating company you use has the test instruments and knowledge to take combustion and CO tests. Simply ask if they do combustion testing with instruments providing a continuous digital readout of Oxygen, Carbon Monoxide and Stack Temperature.
Obviously, when selecting a HVAC company, there are a lot of factors to consider. But at least a company which has invested in the test instruments is demonstrating its commitment to providing a safe and efficient heating system for their customers. That's a pretty good start. It probably also means the company has invested in training personnel to keep up with the changes in the industry - and this industry has changed tremendously in the past several years.
By the way, if you find a contractor with the equipment, have him check your gas fired kitchen oven and range tops for carbon monoxide production. There's a good chance that you will find your furnace flue gasses (which are vented to the outside) are producing lower levels of CO than your oven (which is venting into your kitchen)!