We live with it and joke about it, but, humidity is the main reason for colds, allergies, high utility bills, moldy homes and general discomfort in New Orleans.
It's when you let the humidity level inside your home remain at a high level that problems begin. Consider the facts:
Principal Sources of Higher Humidity
Occupants
Adding only four to six pints of water to the air raises the relative humidity in a 1,000-square-foot home from 15 to 60 percent, assuming the temperature is constant.
- One person’s breathing produces 1/4 cup of water an hour. (Your breath contains hundreds of droplets of invisible water vapor; you see them when you breathe on cold glass.)
- Cooking for a family of four produces approximately five pints of water in 24 hours.
- Showering puts 1/2 pint of water into the air and bathing puts 1/8 pint of water into the air. Center Point Energy
Infiltration
The sum of all outside air that penetrates a house is sometimes referred to as air exchanges per hour.
To get an idea of what your home's air change rate might be, consider that a tight, well sealed newly constructed home usually achieves 0.6 air changes per hour or less. A reasonably tight, well constructed older home typically has an air change rate of about 1 per hour (which is the equivalent of 1/2 ton of air conditioning in the average home). A somewhat loose older home with no storm windows and caulk missing in spots has an air change rate of about 2. A fairly loose, drafty house with no caulk or weatherstripping and entrances used might have an air change rate as high as 4, and a very drafty (raised or) dilapidated house might have an air change rate of as high as 8.
The primary drivers of infiltration in buildings are stack effect, wind effect, combustion effect, exterior ducts, unbalanced supply and return air and exhaust fans. These effects are discussed below:
- Stack effect occurs when warm air rises and pressurizes the upper part of a room or building. As this pressurized air leaks out the top, cool air is drawn into the lower part of the room or building.
- Wind effect occurs as air moves over the top of the building. The moving air increases the pressure on the windward side of the building creating a negative pressure on the leeward side. This pressure difference between the windward and leeward sides of the building drives infiltration.
- Combustion effect occurs when combustion devices such as furnaces use indoor air for combustion, and then expel exhaust gasses through stacks to the outdoors. Air must leak into the building to make up the air lost through the exhaust stack.
- Exterior ducts. In warm climates it is common to run air supply ducts through unconditioned spaces such as attics. Air supply ducts are rarely tightly sealed and typically leak air. Air leaked from supply ducts into unconditioned spaces is replaced through infiltration.
- Unbalanced Supply & Return Air. Furnaces and air conditioners supply conditioned air to rooms and draw return air back to the furnace or air conditioner. When supply and return ducts are not located in the same room, rooms with supply ducts are over-pressurized and rooms with return ducts are under-pressurized. These pressure differences increase air infiltration.
- Kitchen Hoods and Clothes Dryers. Kitchen hoods are sized based upon the btu's of heat produced. Usually this is between 250 and 400 cubic feet of air per minute (cfm). Bathroom ventilation fans typically produce between 200 and 250 cfm. Each can instantly create negative pressure in the home.
- Raised Homes. In homes built on crawl spaces, evaporation of moisture from the earth is a major source of household humidity. The high levels of humidity in crawl spaces can be a problem in both summer and winter. Foul odors in the home or crawl space, mold and mildew growth in the interior of the home (especially in closets) and growth of fungi in the crawl space itself are signs of the problem.
Solutions
Vent humidity produced inside the home by occupants whenever possible. All bathroom vents should have a timer to prevent them from running unnecessarily.
Maximize the dehumidification of your air conditioning system. Variable speed furnaces and air handlers and two stage condensers were designed to increase dehumidification by increasing run time while saving on electricity.
Install a humidistat. Some air conditioning thermostats contain a dehumidification function called a humidistat. A humidistat will increase run time of an air conditioner if a preset humidity level is unmet.
Seal and insulate ducts. Duct systems should be leak free. This is rarely the case but is well worth the expense.
Weatherstrip windows and doors. Windows and doors are a major source of infiltration. They should be made leak free.
Moisture barrier under a raised home. Covering the crawl space ground with a vapor retarder (polyethylene or heavy plastic sheets) is crucial in preventing moisture problems in crawl space homes.
Install a stand-alone, whole house dehumidifier. Dehumidifiers installed with your air conditioner only work when the air conditioner is running. A stand alone system works whenever the humidity in your home is too high, including those times of the year when air conditioning is unnecessary.
Moisture barrier under a raised home. Covering the crawl space ground with a vapor retarder (polyethylene or heavy plastic sheets) is crucial in preventing moisture problems in crawl space homes.
Install a stand-alone, whole house dehumidifier. Dehumidifiers installed with your air conditioner only work when the air conditioner is running. A stand alone system works whenever the humidity in your home is too high, including those times of the year when air conditioning is unnecessary.
Pressurize the house. When everything else fails or is impractical due to cost, consider adding a stand alone economizer/dehumidifier. This type of system will measure the pressure inside the home and increase it to prevent infiltration due to negative pressure. In this system, outside air is cooled and dehumidified and introduced into the home whenever the inside pressure calls for it. This system is a must for raised homes if humidity is a problem.
References:
The problems noted in this post are not unique to the "problem" house. They exist in all homes to a greater or lesser degree. You don't have to address each one but anything you do will have a positive impact on your comfort, your health and your utility bills. Surgi's can help you put together a humidity plan to attack your problems. You'll be surprised at the difference.- Clemson University, "Moisture: Build to Keep It Out of Homes In Warm, Humid Climates"
- University of Dayton, "Infiltration"
- David Darling, "Air Exchanges"
- Michigan State University Extension Services, "Moisture Problems In The Home"
Need a new system? Surgi's can help. Need a healthier, more comfortable life? We can change the way you feel about your home.
Call 469-4232 for a free estimate today!
While you are researching try the following articles on Surgi's website:
