How does insulation work?
"A good insulating material slows the flow of heat transferred in three ways: conduction. convection, and radiation," said Richard B. Hayter, director of Engineering Extension at Kansas State University.
Conduction is the transfer of heat through solid materials; convection, the transfer of heat through a gas, such as air; and radiation, the transfer of heat by electromagnetic waves requiring neither a gas nor a solid for movement.
"Typically, individuals think of a good insulator as one that reduces conduction," Hayter said. "However, other transfer methods can play an important role."
Typically most insulation such as cellulose, fiber glass, and rigid foam used in housing relies on small (in some cases microscopic) dead air spaces within the insulation to slow the flow of heat.
However, other forms of insulation are becoming common in housing as well.
"Reflective insulations slow the flow of heat by reducing radiation," said Hayter. "To be effective, the reflective side of both single- and multiple-layer reflective insulations must face an open dead air space."
When installed in contact with other building materials, reflective insulation will not slow the flow of heat.
Does a solar collector need to be protected from overheating during the summer?
"Unless your collector operates year round, such as for domestic water heating, it should be protected from direct sunlight during the summer," said Doug Walter, extension specialist in residential energy at Kansas State University.
"Although the collector likely won't burst into flames if left unprotected, overheating may damage the seals and working parts. This reduces the collector's life span and performance."
Walter said collectors can be protected by shading them with overhangs or vegetation, by venting the heat, or by covering the glass with a sheet of wood or canvas.
Collectors with vertical surfaces are less susceptible to overheating because considerable solar radiation from the high summer sun reflects off the glazing, but they still need protection, he said.
I recently installed a whole house fan to help cut down on my cooling costs. What is the most effective way to use the fan to cut air conditioning costs?
"A whole house fan will reduce cooling costs only if it is used as a substitute for air conditioning when the outdoor temperature drops below the indoor temperature," said Doug Walter, extension specialist in residential energy at Kansas State University.
A whole house fan and air conditioner should never be operated at the same time because the fan will simply exhaust the cool, dehumidified air.
If you are running your air conditioner, you might want to consider switching over to the fan when the outdoor temperature drops below about 80 degrees. Because this usually happens at night, you could shut your air conditioner off an hour or so before you plan to go to bed.
"When you go to bed, open several windows throughout your house and turn your whole house fan on," Walter said.
The fan should run all night but should be shut off early in the morning before it begins to warm up outside. A timer may be used for this purpose.
In the morning, close windows and doors. Your house may be able to "coast" through much of the morning before the air conditioner needs to be turned on. according to Walter.
How can I reduce the humidity in my home?
"Air conditioners and dehumidifiers help reduce the relative humidity in your home," said Richard Hayter, director of Engineering Extension Programs at Kansas State University.
Because both consume energy in the process, it is to your advantage to reduce the amount of water vapor in your home.
Air leaking into the home from the outdoors contributes to raising your energy costs regardless if it is cold, winter or hot, humid, summer air.
"Air conditioners cool your home as well as remove water vapor from the air," Hayter said. "However, proper maintenance of your air conditioner is critical for proper dehumidification, just as it is for cooling the air. Dust and dirt will significantly reduce airflow past the cooling coils if you do not inspect, clean or replace the filter at regular intervals. Likewise, the drain from the condensate pan must be free of any debris to assure that water does not remain in the pan to be recirculated through the home."
Weatherstripping and caulking will reduce the cost of dehumidifying your house, as will exhausting the humid air from the bathroom during showering and over the kitchen range while preparing meals.
How important is foundation insulation?
"As a general rule, in new construction, you should install foundation insulation or floor insulation," said Gene Meyer, extension mechanical engineer at Kansas State University. "If you have to retrofit the insulation, then you will need to consider what choices are available and what the benefits will be."
Three types of foundation are used today: slab-on-grade, crawl space, and a conventional basement.
Because slab-on-grade foundations lose heat primarily around the edge of the slab, perimeter insulation would help slow the heat loss.
Perimeter insulation is easy to install in new construction, but retrofitting perimeter insulation can be costly because it requires digging around the entire foundation. Perimeter insulation should extend from the top of the foundation to at least the frost line and should consist of two to four inches of a rigid polystyrene type of insulation.
"To improve the comfort of slab-on-grade floors, place one inch of polystyrene under the outer edge of the slab so that it extends inward for four feet," Meyer said.
If your home has a crawl space, you can insulate either the floor directly above the crawl space or the foundation walls. The choice depends on the location of water lines and access to the crawl space.
Foundation walls can be insulated on the inside with fiber glass batts or on the outside with rigid polystyrene insulation.
If you heat the basement or if there are water lines in the basement that might freeze, the basement wall should be insulated from either the inside or outside. To be effective, the insulation should extend to at least the frost line (two to three feet below grade), but insulating the entire wall is preferred.
If you use polystyrene board or insulating sheathing on the inside, you must cover it with one half inch of sheet rock to meet code regulations.
"If you choose to insulate the floors above the basement, use a 6-inch batt ( 19)," Meyer said. "If you insulate the walls, a minimum of 2 inches of polystyrene or 3½ inches of fiber glass batts should be used."
What can be done to minimize energy lost through skylights?
"Skylights present at least three energy problems," said Doug Walter, extension specialist in residential energy at Kansas State University.
"To apply the plastic, use double-stick tape, then stretch it tight by heating it with a blow dryer," Walter said. "By applying the plastic over the frame, you also reduce air leakage."
Movable insulation, made by cutting a piece of rigid insulation to fit the skylight opening, can be pressed into the skylight frame at night, then removed in the morning.
Preventing sunlight from striking the skylight is the best way to control unwanted heat gain. This can be done with vegetation or seasonally applied covers, such as a solar screen.
"You can also reflected sunlight from the inside by using light- colored Venetian blinds, a roller shade, or movable insulation with a reflective backing," Walter said.
Will adding insulation to an already insulated surface decrease the overall R-value?
"Adding loose-fill or flexible insulation such as cellulose or fiber glass over existing insulation will only slightly compress the existing insulation, and the loss in R-value will be insignificant," said Richard B. Hayter, director of Engineering Extension at Kansas State University.
The benefit of the new insulation far overshadows any minor loss due to the compression.