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Combustion safety and your propane, natural gas, fuel oil furnace or boiler


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Combustion safety and your heating system

combustion equals flame

Combustion Safety Basics (a refresher or primer)


If you have a natural gas, propane, fuel oil (oil or kerosene) fueled furnace or a boiler system, you should know some basics. We know the rest!


We at Phoenix Heating and Air are highly trained professionals, trained in combustion safety. We care about you and want you to have a safe home, and that starts with a safe heating system.



Combustion: rapid chemical combination of fuel with oxygen, involving the production of heat.


Combustion happens within your furnace or boiler. Combustion is what creates the flame. It is a process of fuel, ignition, and oxygen. To have proper combustion you must have proper ventilation, proper gas pressure or proper oil flow to the unit, proper air pressure, and more. Your furnace produces many chemicals during this process, and they are harmful to your health to breathe. That is why you need proper ventilation. Improper ventilation can lead to disaster.


Ventilation is bringing good air into the system, and exhausting bad air out the flue. Proper ventilation is so that it runs properly with good airflow and is essential to safety. Unvented fuel appliances are a health hazard. We will go in depth into ventilation next week.


Fuel to air ratio

Your furnace or boiler, no matter how new or old needs regular inspection and maintenance to make sure it is properly combining fuel and air and not running too rich or too lean.



Too lean. Did you know having too much of a good thing isn't always good?

The Leaning Tower of Pisa
Not this kind of lean

A lot of newer, high efficiency systems are designed to run lean but like everything, there is a limit to how lean a system should run. Running too lean is when you have a lot of oxygen and very little fuel. This makes your system not burn fuel the way it should. Too lean causes incomplete combustion, or not enough combustion to keep the flame going like it should. Running too lean also causes excess gasses called nitrogen oxides, which are poisonous gasses. These gasses are similar to what comes out of your car's exhaust pipe. You don't want that kind of air to breathe in your house, so it must be properly vented outside. We will look more into ventilation next time.


Too rich? How can I be too rich? Your fuel burning heating system can be running too rich, and that is a bad thing!


Wad of money
Not this kind of rich!

A system that is running too rich is one that leaves unburned fuel inside your unit and your flue in the form of soot, that when exposed to oxygen may burst into flames, causing a flame where it is not wanted. In other words, it may start an explosion. Too much fuel coming in with not enough air causes a buildup of gas and can cause gasses to build up inside the flue.


Getting things just right

The proper balance of the fuel and oxygen levels is essential to safety, health and cost of use of your system. We test and adjust (if needed) this balance during maintenance visits.


Gas and other pressures



If you are using natural gas or propane to heat your home, the pressure of the gas is regulated by the gas pressure valve. The gas pressure need to be tested regularly to avoid damaging the system among other hazards. They may need adjustment periodically.

gas pressure guage

Gas Pressure


If the gas pressure is too low, it will lead to more condensation inside the unit which can cause corrosion, cracks, and rust in the heat exchanger. These damages lead to deadly gasses escaping into the home and possibly even explosion.


If the gas pressure is too high, it can cause overheating within the unit. This overheating can cause internal component failure which also may cause gas and CO2 leaks in the system. Burning smells, the furnace powering up and down frequently, or stops altogether, can indicate a high-pressure situation.



Boiler Water pressure


Boilers heat water by combustion of fuel oils, propane or natural gas. The heated water in the tank is also under pressure. This pressure should stay within normal range. See our blog online soon, or in your inbox if you are subscribed, to find out more about boiler safety.


Oil pumps and pressure


Oil burning boilers use oil pumps to push the fuel to the burner. Oil pumps need a clean filter to maintain pressure, or what we call prime. Sometimes these filters can get so clogged that the debris gets pulled through the line and that can cause a bigger problem. This filter should be checked regularly and replaced when it is due.


pipes, valves and gauges

Oil lines can develop leaks through corrosion or damage from digging. If air enters the line due to a leak or loose nozzle or fitting, that will also make the pump lose prime. Again, not wanting the system to run too lean to make combustion, and not too rich to cause excess fuel in the system is essential.


A safe system is quiet, but a quiet system is not always safe


Oil pumps going out sometimes make audible noises such as popping, rattling, screeching, slamming or banging. The rooms in your house may be cooler than you’ve set the thermostat to, or different rooms feel different temperatures.

kettle on stove makes a kettling sound

Boilers and fuel furnaces that need immediate attention are ones that are kettling, or making other odd noises, leaking any fluids, failure to start, a metallic, burning or rotten egg smell, the pilot light keeps going out, or if it is not heating properly. These can be signs of something seriously wrong with your boiler or furnace. Call us right away and get it looked at before the problem it has gets worse. We will go more in depth about Boilers soon.


A gas furnace that is hissing, popping, banging or making any other noise should be inspected right away to be safe.

our professionals test everything

Most problems start silently, and by the time you can hear them it is a bigger problem. Routine maintenance helps find these silent problems before they can be heard. Having a working, tested CO alarm helps protect you in case of gas leaks. If you alarm goes off, get to fresh air fast!


Heating systems should be seen and not heard


If you hear any noises coming from your heating system, no matter which type you have, please call us right away so we can get that system running safely. A safe system is quiet, but a quiet system is not always safe. Have your heating system maintenance done regularly to make sure it is safe.


Our technicians make sure your system runs safely

Fixing the common and uncommon emergency furnace issues 24/7


We are highly trained to deal with combustion issues that are not easily or safely done by homeowners. We go through your system checking for leaks, parts that are wearing out, testing & adjusting the fuel and boiler tank pressures correctly and making sure your system is safe to run. Most major issues with boilers and gas furnaces can be avoided with proper care and maintenance.

We have professional technicians trained in combustion safety to make sure your system is running with peak performance and safety. Text or call us today to make an appointment to have your furnace or boiler maintenance done soon to avoid dangerous and costly situations with your system. Call or text us at any time, 24/7 if you have a heating or plumbing emergency and fill out this form for a maintenance request or if you have something odd going on with your heating system you'd like us to look at.



Stay tuned for more about ventilation safety next time. Soon, we will discuss more boiler safety. Find out what makes a boiler an efficient heating system, and why you might want one in the future, if you don't have one now.


Feel free to share this blog article with the world (or just on social media, and with family and friends). Thanks for reading. Stay safe!


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