Ask Energenie

September 1999

Contents

1. What is the status of the refrigerant used in my home air conditioner? Is it being phased out like the refrigerant in my car?

2. Should I seal off my attic vents to conserve heat in the winter?

3. I am thinking of using wood to heat my home. What are some types of wood burning systems I might choose, and what are some maintenance precautions?

4. I'm building a new home. From a year-round energy perspective, what is the best direction to orient it?

5. The walls of my new house will be built with inch-thick foil-faced sheathing on the outside and a 6-millimeter-thick plastic vapor barrier on the inside. Is this going to cause moisture problems?

6. I have several single-pane windows in my home and would like to replace them with more efficient units. What are some common window types and their r-values?

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1. What is the status of the refrigerant used in my home air conditioner? Is it being phased out like the refrigerant in my car?

"Unless your central home air conditioner is relatively new, the refrigerant is R22. It is chemically different from the refrigerant used in your auto, and has only one-twentieth the impact on stratospheric ozone," said Gene Meyer, extension mechanical engineer at Kansas State University. "Because it is not as harmful to the ozone layer, it is not scheduled for phase out until 2020."

Some air conditioner manufacturers are offering equipment filled with refrigerants that pose no harm to the atmosphere. The operating efficiency of these air-conditioners is no higher than those filled with R22.

"These products may carry a higher price but the refrigerants will be available after the scheduled 2020 phase-out of R22," Meyer said.

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2. Should I seal off my attic vents to conserve heat in the winter?

"No," said Doug Walter, extension specialist in residential energy at Kansas State University. "Attic ventilation is important in winter as well as summer to remove moisture that leaks into the attic from the living space below."

Normal household activities such as bathing, cooking, and cleaning generate moisture. Also, people and plants give off significant amounts of moisture.

"This moisture enters the attic space through the ceiling, and through leaks around light fixtures, flue pipes, and other openings into the attic," Walter said.

Ventilation carries the moisture away before it can accumulate and damage the insulation and roof structure. Your attic should have one square inch of open vent area for every square foot of attic floor area.

"Vents should be well-distributed, with both high and low openings," he said.

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3. I am thinking of using wood to heat my home. What are some types of wood burning systems I might choose, and what are some maintenance precautions?

"The most traditional type of wood burning system is the fireplace. However, a fireplace is only zero to 20 percent efficient as a heating device because most of the generated heat goes up the chimney," said Richard Nelson, extension specialist at Kansas State University.

"Another drawback of the conventional fireplace is air infiltration through the chimney. An alternative to the fireplace is a wood stove or furnace, which can have efficiencies as high as 60 percent," he said.

A wood stove transfers heat by radiation or convection. A radiative wood stove generates heat to nearby surfaces and warms the air around the stove. This type of stove is appropriate for heating a single room or small living space.

A convective wood stove (circulating type) is a double-walled stove with an air space between the walls. A blower or fan distributes the heat to other rooms or helps heat a larger space. This type of stove has a much cooler surface, thereby reducing the potential for burns and fire hazards.

"Another type of wood heating device is a wood furnace. A wood furnace is similar to a gas or oil forced-air furnace except, of course, that it burns wood. The differences are in size and heating capacity," Nelson said.

A wood furnace can be used with a conventional furnace in what is referred to as a dual-fired system. In this system, as the wood burns down, the temperature drops and the secondary system fires to supply the needed heat. Thus, the conventional heating system is not operating all the time.

Nelson noted an advantage to this system: It allows for retrofitting of wood systems to an existing fuel-fired system. This means that with the addition of a few parts and equipment, a wood system can be adapted to a fuel-fired system. "With all wood burning systems, take precautions to insure safe operation, " Nelson said.

Maintain adequate ventilation not only for proper combustion but to ventilate any exhaust fumes. Periodically clean the combustion chamber to remove the creosote build-up that can cause fires. Finally, cleaning the flue is important to reduce risk of chimney fires.

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4. I'm building a new home. From a year-round energy perspective, what is the best direction to orient it?

"For best year-round energy performance, the long axis of your house should run east and west, and the facade with the most window area should face within 30 degrees of true south," said Doug Walter, president of Kansas Building Science Institute, Manhattan.

South-facing windows are net energy gainers. That is, they admit more heat from solar energy than they lose during winter.

"In summer, you can protect them from heat gain with a simple overhang or other shading device," Walter said.

Windows facing any other direction are net energy losers. Unshaded east- and west-facing windows admit unwanted solar heat during summer. Furthermore, they are difficult to shade effectively.

"Don't exclude windows on the east, north and west sides of your new home, however," he said. "They provide natural light, cross-ventilation, views and emergency exit from bedrooms. Simply limit the size and quantity of windows that do not face south."

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5. The walls of my new house will be built with inch-thick foil-faced sheathing on the outside and a 6-millimeter-thick plastic vapor barrier on the inside. Is this going to cause moisture problems?

"It depends on the quality of the two materials and how they are installed," said Bruce Snead, extension specialist in residential energy at Kansas State University.

"If warm, moisture-laden interior air finds its way into the wall, it could condense on the inside face of the sheathing if the surface is sufficiently cool," he said. "However, if the inside vapor barrier is carefully installed and sealed to prevent air leaks, the possibility of moisture getting into the wall is reduced."

Another factor affecting the potential for moisture problems is the temperature of the inner foil face. If the sheathing has a high R-value, the foil face probably won't be cold enough to cause condensation.

"Also, outside air flowing through openings in the wall caused by shoddy construction may lead to cold spots and condensation on the interior wall," Snead said.

Both the vapor barrier and the sheathing should be installed to be as airtight as possible to prevent air and moisture flow into the wall cavity. Tape seams, corners and butt joints to create an airtight wall.

Poor construction can cause problems with any building assembly, but especially in energy-efficient construction where interior moisture levels are likely to be high. Snead said careful attention to details and evaluating how they will respond to air and moisture are necessary to avoid these problems.

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6. I have several single-pane windows in my home and would like to replace them with more efficient units. What are some common window types and their r-values?

R-value is a measure of a material's resistance to temperature change.

In a well insulated home, floors typically have an R-value between 11 and 19; walls, 19 to 27; and ceilings, 30 to 45. The highest R-value for a window, even one with multiple panes and tights seals, is only three to four.

"The single-pane windows in your home probably have an R-value of slightly less than one," said Richard Nelson, extension specialist at Kansas State University. "Adding another pane of glass (referred to as double-glazing), will raise the R-value to slightly more than two."

The technique of double-glazing creates an air space between the panes of glass. This air space reduces conductive heat loss through the window.

By adding yet another pane of glass (triple glazing), the R-value increases to about 3.2.

"The addition of glass panes should not be confused with adding storm windows to the outside of the window frame," Nelson said.

The R-value of window units is the resistance to heat flow at the center of the glass, and this is generally higher than overall R-value of the window.

"The overall R-value of a window includes the glass or glazing, the frame and the sash," Nelson said.

One common method of reducing heat gain or loss through windows is by coating the glass with an invisible, heat-reflective material. This type of glass is called low-emissivity, or low-e, glass.

"Emissivity is a measure of the amount of heat radiating from a surface. Therefore, the lower the emissivity, the better," he said.

A double-pane window with a low-e coating has an R-value of about 2.8, which translates to 35 percent less heat gain or loss than conventional double-pane windows. Triple-pane, low-e window units are also available and have a rating of approximately R-4.

Nelson said another type of window that's becoming more popular is a low-e, double-pane unit that has a cavity between the panes filled with a gas, such as argon.

Argon is an environmentally safe gas found naturally in the atmosphere.

"Argon is less dense than air, so it conducts less heat," he said. "Thus, a double-pane window unit with argon loses less heat than does a double-pane window filled with air."

Several major window manufacturers are now filling all of their low-e, double-pane windows with argon.

"However, while the R-value increases through the addition of multiple panes of glass or low-e coatings or gas fills," Nelson said, "the cost also increased and, depending on the type of home you have and other factors, it may not be cost-effective for you to install higher R-value windows."

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Ask Energenie is produced by the Kansas Energy Extension Service through Kansas State University. This material was prepared with the support of the U.S. Department of Energy (DOE) Grant No. DE-FG48-97R802102. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the view of DOE.