- Home
- For the homeowner
- Safety
- Definitions
- Gas furnace
- Some error codes for gas furnaces
- Service sheet for the gas furnace
- gas furnace design
- The gas heat exchanger
- Dangerous conditions in gas furnaces
- Annual service of the gas furnace
- Repair procedures for gas furnaces
- Gas fireplace millivolt systems
- Oil furnace
- Setting gas input
- Quick tips for troubleshooting furnaces
- Troubleshoot
- Operation and troubleshoot furnace by manufacturer
- HVAC war stories blog
- Annual service of an oil furnace
- Oil furnace design
- Oil furnace troubleshoot
- Repair procedures for oil furnaces
- Gas code training
- Piping and connections
- FAG w pilot no fire
- Combustion analysis
- Electric furnace
- Air conditioner
- Refrigeration
- Heat Pump
- Boiler
- Ductwork design and troubleshoot
- Thermostats
- Diagnostic problems
- Tools
- Electric test meters
- Electrical diagram training
- Electrical symbols
- Single and 3 phase power systems
- Electric wiring solutions
- Transformer design and troubleshoot
- Electronic air cleaner
- Blowers and fans design & troubleshoot
- Humidity and humidifiers
- Furnace, Air Conditioner and part manuals
- Electric motors
- Run Capacitors
- Start capacitors
- Troubleshooting the capacitor
- Gas furnace short cycling
What is natural gas and propane
What is natural gas?
Simply it is a gaseous fuel associated with liquid petroleum.
In earlier times, it was considered a waste gas and was burned off at the well head.
It was also not the first fuel gas that was distributed to homes and businesses.
In most cases, coal gas was the first gas used. Coal gas was produced by heating coal thus driving off the coal gas. It was used for lights and heating appliances. Coal gas had a large amount of Carbon Monoxide. When you hear of someone turning on the gas to commit suicide, it was coal gas they were using. If you tried the same thing with natural gas, you would not die of CO poisoning, but you might blow up the whole building taking all others with you! When pipelines were installed, natural gas became popular. It is primarily methane with some carbon dioxide, nitrogen and and in some areas, hydrogen sulfide.
Simply it is a gaseous fuel associated with liquid petroleum.
In earlier times, it was considered a waste gas and was burned off at the well head.
It was also not the first fuel gas that was distributed to homes and businesses.
In most cases, coal gas was the first gas used. Coal gas was produced by heating coal thus driving off the coal gas. It was used for lights and heating appliances. Coal gas had a large amount of Carbon Monoxide. When you hear of someone turning on the gas to commit suicide, it was coal gas they were using. If you tried the same thing with natural gas, you would not die of CO poisoning, but you might blow up the whole building taking all others with you! When pipelines were installed, natural gas became popular. It is primarily methane with some carbon dioxide, nitrogen and and in some areas, hydrogen sulfide.
Some facts about natural gas
Ignition temperature: 1100 to 1200 degrees F, 593 to 648 degrees C
Concentration for ignition: 4 to 14%. This means that if there is less than 4% in the air combustion will not occur. If there is more than 14% in the air combustion will not occur.
Natural gas is odorless, colorless and tasteless. (An odor is added to the gas at the utility to indicate its presence).
Natural gas is lighter than air, so it tends to rise to the highest part of the room if it leaks.
Natural gas is not poisonous but if there is a large amount in an enclosed area it will displace the oxygen in the air and you can die from lack of oxygen.
Any leak is dangerous. If you smell gas, evacuate the building.
When natural gas burns, the products of complete combustion are: carbon dioxide, water and heat.
When the gas burns, there is normally excess air. Excess air is needed to insure complete combustion. Excess air percentages can be from 20% to 50%.
In modern furnaces, excess air is somewhat lower because more excess air cools the flame down and reduces efficiency.
Natural gas is sold by therms. A therm is enough gas to produce 100,000 BTU.
The natural gas meter delivers the gas by cu ft.
The number of BTUs in a cu ft varies with the region. In many areas, the number of BTUs per cu ft is 1000. So that means the 1 cu ft meter dial would rotate 100 times to use 1 therm.
Gas furnaces are sized by the number of BTUs that go into the furnace. This is called BTU input.
We can use the meter to determine what the gas input is by recording the time it takes the meter dial to rotate one complete turn. For a more complete discussion of setting gas input to an appliance click here
Concentration for ignition: 4 to 14%. This means that if there is less than 4% in the air combustion will not occur. If there is more than 14% in the air combustion will not occur.
Natural gas is odorless, colorless and tasteless. (An odor is added to the gas at the utility to indicate its presence).
Natural gas is lighter than air, so it tends to rise to the highest part of the room if it leaks.
Natural gas is not poisonous but if there is a large amount in an enclosed area it will displace the oxygen in the air and you can die from lack of oxygen.
Any leak is dangerous. If you smell gas, evacuate the building.
When natural gas burns, the products of complete combustion are: carbon dioxide, water and heat.
When the gas burns, there is normally excess air. Excess air is needed to insure complete combustion. Excess air percentages can be from 20% to 50%.
In modern furnaces, excess air is somewhat lower because more excess air cools the flame down and reduces efficiency.
Natural gas is sold by therms. A therm is enough gas to produce 100,000 BTU.
The natural gas meter delivers the gas by cu ft.
The number of BTUs in a cu ft varies with the region. In many areas, the number of BTUs per cu ft is 1000. So that means the 1 cu ft meter dial would rotate 100 times to use 1 therm.
Gas furnaces are sized by the number of BTUs that go into the furnace. This is called BTU input.
We can use the meter to determine what the gas input is by recording the time it takes the meter dial to rotate one complete turn. For a more complete discussion of setting gas input to an appliance click here
|
What is propane?
Propane is also a petroleum derived fuel. It is also called liquified petroleum gas orLPG.
In most cases, there is a pressure vessel located at the site designed for propane. Propane is a liquid when supplied and is boiled to produce gaseous propane for use in the furnace. It is sold by the gallon as a liquid. When propane leaves the cylinder, it must be a gas, so it is taken out of the top of the cylinder. It then goes to a regulator that reduces it pressure to 11 inches water column . When determining how much gas is flowing to the furnace, you must use a manometer to be sure the pressure is 11 in wc. |
Some facts about propane
In order to ignite, the propane-air mix must contain from 2.2 to 9.6 percent propane vapor.
Propane won’t ignite when combined with air unless the source of ignition reaches at least 940 degrees F.
Propane is odorless, colorless and tasteless. (As with natural gas, an odor is added to the gas at the utility to indicate its presence).
As with natural gas, The products of complete combustion are: carbon dioxide, water and heat.
Propane has 2500 BTUs of heat per cubic foot at 11" water column.
Propane has more a tendency to create soot if it does not have enough combustion air.
It is heavier than air, so it ends to drop to the lowest part of the room.
Propane is not poisonous but as with any gas, if there is enough in the room, it will displace the oxygen and you could be suffocated.
When considering safety around this gas, any leak is dangerous. If you smell gas, evacuate the building!
Propane, because it is a liquid when delivered, must boil before it can be used. When it boils, it cools. At atmospheric pressure it boils at -30F. What this means is if it is very cold, the liquid may reach -30F and no more gas will flow. If this condition is reached, either the cylinder must be warmed or a delivery of gas may be necessary. Because warming the cylinder may be dangerous, when there is a cold snap coming, sometimes it is best to have the cylinder filled.
Propane won’t ignite when combined with air unless the source of ignition reaches at least 940 degrees F.
Propane is odorless, colorless and tasteless. (As with natural gas, an odor is added to the gas at the utility to indicate its presence).
As with natural gas, The products of complete combustion are: carbon dioxide, water and heat.
Propane has 2500 BTUs of heat per cubic foot at 11" water column.
Propane has more a tendency to create soot if it does not have enough combustion air.
It is heavier than air, so it ends to drop to the lowest part of the room.
Propane is not poisonous but as with any gas, if there is enough in the room, it will displace the oxygen and you could be suffocated.
When considering safety around this gas, any leak is dangerous. If you smell gas, evacuate the building!
Propane, because it is a liquid when delivered, must boil before it can be used. When it boils, it cools. At atmospheric pressure it boils at -30F. What this means is if it is very cold, the liquid may reach -30F and no more gas will flow. If this condition is reached, either the cylinder must be warmed or a delivery of gas may be necessary. Because warming the cylinder may be dangerous, when there is a cold snap coming, sometimes it is best to have the cylinder filled.
A gas furnace uses either natural gas or propane as a fuel. The furnace must be designed and built for either propane or natural gas. If one is to be converted from one gas to the other, the manufacturer must list the furnace for conversion and the proper conversion kit must be used.
With propane having 2500 BTU per cu ft and natural gas having approximately 1000 BTU per cu ft, the manifold pressure and burner orifices are very different. As an example, if propane were used in a furnace set up for natural gas, the orifices would be much too large and the furnace would be overfired. This will cause the heat exchanger to be damaged from the excess heat. It could also cause a fire.
With propane having 2500 BTU per cu ft and natural gas having approximately 1000 BTU per cu ft, the manifold pressure and burner orifices are very different. As an example, if propane were used in a furnace set up for natural gas, the orifices would be much too large and the furnace would be overfired. This will cause the heat exchanger to be damaged from the excess heat. It could also cause a fire.
Types of flames
As with all fuels, they must be a gas to burn. Both these fuels are gaseous when they are supplied to the appliance. This makes it very easy to prepare them for combustion.
There are 2 types of burner flames. The blue flame and the yellow flame.
The yellow flame is not premixed with air. The gas simply comes out of a pipe. As the gas comes out of the pipe, it mixes with the surrounding air and burns from the outside in. This produces a lazy yellow flame. If the flame does not touch any metal, the gas burns completely. If primary air is supplied, the flame is smaller and blue. This flame is better for heating applications as it does not take up as much space to complete the burn and is easier to control. A demonstration of this type of burner and the blue flame burner is in the video below.
There are 2 types of burner flames. The blue flame and the yellow flame.
The yellow flame is not premixed with air. The gas simply comes out of a pipe. As the gas comes out of the pipe, it mixes with the surrounding air and burns from the outside in. This produces a lazy yellow flame. If the flame does not touch any metal, the gas burns completely. If primary air is supplied, the flame is smaller and blue. This flame is better for heating applications as it does not take up as much space to complete the burn and is easier to control. A demonstration of this type of burner and the blue flame burner is in the video below.