- 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
Humidity and humidifiers
Humidity is defined as the amount moisture in air compared to the amount that the air can hold, expressed as a percentage.
The video below demonstrates how to measure the amount of moisture in the air using a wet bulb and dry bulb thermometer.
The terms wet bulb and dry bulb are defined as follows:
Dry bulb: A thermometer placed to sense temperature of the air.
Wet bulb: An identical thermometer placed near the dry bulb thermometer with a cloth "sock" placed around the sensing probe of the thermometer that is wetted by water.
When the 2 probes are placed in moving air, the wet bulb will read a cooler temperature than the dry bulb due to the evaporation of the water on the wet bulb. The rate of evaporation depends on the the humidity in the air passing over the bulb.
If the humidity is high, the rate of evaporation for a given amount of time will be low and the temperature difference between the 2 thermometers will be low.
If the humidity is low, the rate of evaporation will be high and the temperature difference will be high.
If the humidity is 100% the temperatures of the 2 thermometers will be the same.
The video below demonstrates how to measure the amount of moisture in the air using a wet bulb and dry bulb thermometer.
The terms wet bulb and dry bulb are defined as follows:
Dry bulb: A thermometer placed to sense temperature of the air.
Wet bulb: An identical thermometer placed near the dry bulb thermometer with a cloth "sock" placed around the sensing probe of the thermometer that is wetted by water.
When the 2 probes are placed in moving air, the wet bulb will read a cooler temperature than the dry bulb due to the evaporation of the water on the wet bulb. The rate of evaporation depends on the the humidity in the air passing over the bulb.
If the humidity is high, the rate of evaporation for a given amount of time will be low and the temperature difference between the 2 thermometers will be low.
If the humidity is low, the rate of evaporation will be high and the temperature difference will be high.
If the humidity is 100% the temperatures of the 2 thermometers will be the same.
Relative humidity
When moisture is absorbed into the air, it fills the spaces between the air molecules. Of course air is not only one type of molecule but a mixture of several.
As the air temperature increases, the molecules move farther apart.
The farther apart the molecules are, the more moisture it can hold. So warm air can hold much more moisture than cold air.
Humidity is then "relative" to the temperature.
An example of this is morning dew. The air during the day is warmer than at night. So it can absorb more moisture. Then, at night the temperature reduces and the ability of the air to absorb moisture is reduces. If the temperature drop is high enough, the dew point is reached (100% humidity) and the excess moisture condenses out of the air.
The video below attempts to explain in simple terms how this works.
As the air temperature increases, the molecules move farther apart.
The farther apart the molecules are, the more moisture it can hold. So warm air can hold much more moisture than cold air.
Humidity is then "relative" to the temperature.
An example of this is morning dew. The air during the day is warmer than at night. So it can absorb more moisture. Then, at night the temperature reduces and the ability of the air to absorb moisture is reduces. If the temperature drop is high enough, the dew point is reached (100% humidity) and the excess moisture condenses out of the air.
The video below attempts to explain in simple terms how this works.
Air conditioning as a humidifier
Why do we call it air conditioning instead of air cooling?
The air conditioner cools and dehumidifies the air. So, how does it do it? When air enters the air handler at, say 80 degrees and 50% humidity. It then is cooled when it passes through the air conditioning coil. As was seen in the previous video, the lower temperature of the air will increase the relative humidity of the air. In the case of the temperature drop of 20 degrees as seen below, the air reaches 100% humidity, so some of the moisture condenses out of the air. When the air passes into the structure, it mixes with the existing air. Because the air from the air handler has less total moisture in it, the relative humidity of the structure is lowered.
If the location is in a high humidity area, this will reduce the structure humidity and reduce problems such as mold.
If the humidity is very low in the area, it can cause negative effects such as dry throat, increased asthma symptoms and furniture damage.
The video below illustrates how this works.
The air conditioner cools and dehumidifies the air. So, how does it do it? When air enters the air handler at, say 80 degrees and 50% humidity. It then is cooled when it passes through the air conditioning coil. As was seen in the previous video, the lower temperature of the air will increase the relative humidity of the air. In the case of the temperature drop of 20 degrees as seen below, the air reaches 100% humidity, so some of the moisture condenses out of the air. When the air passes into the structure, it mixes with the existing air. Because the air from the air handler has less total moisture in it, the relative humidity of the structure is lowered.
If the location is in a high humidity area, this will reduce the structure humidity and reduce problems such as mold.
If the humidity is very low in the area, it can cause negative effects such as dry throat, increased asthma symptoms and furniture damage.
The video below illustrates how this works.
In the winter the humidity in northern areas drops very low.
The reason for this is the lower temperature will hold less moisture the colder it gets.
As all structures leak air into them from outside, the air leaking in with, say 30% humidity, will be warmed to the structure temperature. Because the warmed air still has the same amount of moisture in it as when it was outside, the relative humidity will be much lower. Perhaps on the order of 5%. It then mixes with the air in the structure and reduces its relative humidity.
Counteracting this are humidity sources in the structure. Showers taken, meals cooked and people sweating are all sources of humidity inside.
When humidity in the winter reaches unacceptable levels, a humidifier may be added.
The video below illustrates this problem.
The reason for this is the lower temperature will hold less moisture the colder it gets.
As all structures leak air into them from outside, the air leaking in with, say 30% humidity, will be warmed to the structure temperature. Because the warmed air still has the same amount of moisture in it as when it was outside, the relative humidity will be much lower. Perhaps on the order of 5%. It then mixes with the air in the structure and reduces its relative humidity.
Counteracting this are humidity sources in the structure. Showers taken, meals cooked and people sweating are all sources of humidity inside.
When humidity in the winter reaches unacceptable levels, a humidifier may be added.
The video below illustrates this problem.
More coming