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This article was originally published in the January/February 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

 

 

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Home Energy Magazine Online January/February 1995

Energy-Efficient Remodeling--
Grab the Opportunity!

In this issue we begin a regular series on energy-efficient remodeling that will eventually find its way into a book on the same subject.

The opening article is an introduction to the first and most important lesson on energy-efficient remodeling: The house is a system. If a change is made in one area of a house it can affect other areas and result in an unexpected change in energy use.

In future articles we will be taking a close look at specific remodeling projects and how the fundamental principles presented here can be applied in each case.




 

by Karina Lutz

Homeowners and contractors who plan to remodel must consider the house as a system, rather than an assemblage of separate parts. Any change to the mechanical systems, the enclosure, or the site, can have a profound impact on the house as a whole. (From How Buildings Work: The Natural Order of Architecture by Edward Allen. Copyright (c) 1980 by Oxford University Press Inc. Reprinted by permission.)  

Let's face it, when people plan a home remodeling project, it's lucky if energy efficiency ranks ahead of the color of the refrigerator. This is unfortunate because remodeling offer terrific opportunities for improving energy efficiency with minimal additional cost and inconvenience.

Thoughtful remodels can deliver big savings--as much as 50% for certain end uses--that can readily be seen on lower utility bills. Remodeling is the time to take advantage of the energy-saving measures that can be installed more easily and cheaply while construction is underway.

THE HOUSE IS A SYSTEM

Every home is unique, but most remodels fit into fairly standard categories. By far the most popular rooms to remodel are kitchens and bathrooms. Even more common, though, are improvements that don't affect appearance or function, like re-roofing or replacing major equipment. No matter where the change occurs, there is a good chance it will affect how the house functions as a system. The difference is often subtle yet can have a surprising influence on energy use, comfort and safety. That's why it is important to take a whole-house approach--looking beyond the remodeling job at hand and taking into account all the components that make the home a system: the occupants; the building envelope; the heating, ventilation, and air conditioning (HVAC) system; appliances; climate; and landscape.

FIRST STOP: THE UTILITY BILL

From an energy perspective, the utility bill says it all. A few sheets of paper reveal how much it costs to heat, cool, illuminate, power that refrigerator, and provide the other essential services in a house. (Of course, it doesn't indicate how successfully those services are supplied.) Most utilities will provide a summary of the last year's electricity, gas, and oil bills with a phone or written request.

A high annual utility bill means that there are more opportunities to save. An energy audit, if offered by the utility, can help in understanding where the energy goes. Even without an audit, it is easy to graph energy bills. Try to separate the energy used for space heating and cooling from the year-round amount devoted to the water heater, refrigerators, lights, etc.

Most people are surprised how much energy is used regardless of the season. Typically people overestimate the amount of energy devoted to space heating and cooling, and underestimate the amount consumed by the water heater, refrigerator, and lighting. These appliances have a nearly constant energy use year round, and implications for retrofits in the kitchen, bathrooms, and water heating system. With the information from the utility bills in hand, it's possible to estimate likely savings from specific improvements.

Keep in mind that houses are often used differently after a remodel, so utility bills may increase if the house is enlarged or new services added. Remodels are frequently undertaken in anticipation of a change, like a baby. There are (documented) tales of a family's first baby doubling a house's energy use due to the increased laundry, higher thermostat settings, and simply greater presence of people in the house. Retirement can cause similar changes. If activity around the house will increase after the remodel, more energy efficiency actions may be warranted than suggested by a utility bill history.

WHAT WE CAN LEARN FROM UTILITY BILLS

 
The utility bill can be a versatile tool for the homeowner or remodeler, especially if the information is graphed in an easily readable format. Lights and appliances that operate fairly consistently throughout the year (refrigerators, water heaters, cooking and laundry equipment, televisions, and so on) form a base year-round usage. The seasonal energy consumption of heating and cooling equipment is usually evident as peaks above the year-round baseline.

The monthly electricity and gas consumption for a sample house is shown here. The natural gas graph (lower chart) indicates a year-round usage of about 35 therms per month for a gas water heater, clothes dryer and stove. Gas space heating accounts for the higher winter consumption--up 85 therms, from 35 to 120--in January. The electricity graph (upper chart), on the other hand, shows a high year-round usage with a slight summer cooling peak and some increased winter usage for the furnace fan and added winter lighting. To reduce these bills, this homeowner should target the areas of high usage-gas space heating and the appliances that contribute to the high year-round electricity consumption (in this case a waterbed, security lighting, and a second refrigerator).

THERMAL COMFORT--THE GOAL OF A SUCCESSFUL REMODEL

Houses are supposed to keep occupants comfortable, yet people are always complaining that they are too hot, too cold, or feel a draft someplace. A successful remodel should reduce those complaints (or at least not introduce more of them). Most improvements in thermal comfort save energy or, put another way, whole-house energy-efficiency measures usually result in greater comfort. These benefits can be obtained in both heating and cooling situations. In both cases, however, the house must be treated as a whole system because the cause of discomfort may be far away from where it is actually felt.

Thermal comfort is determined by more than just air temperature. In fact, some of the most frequent comfort complaints are caused by other factors, such as radiant temperature and air movement.

The radiant temperature of the interior surfaces of a house have a surprisingly large impact on thermal comfort. In heating or cooling a house, the goal should be to make the surfaces as close as possible to the room air temperature. A poorly insulated house in the winter will have wall surfaces as much as 15 degrees cooler than the room. Adding insulation (in the walls, ceiling, and floor) greatly raises the inside surface temperatures. People often remark that a house feels warmer after being insulated, even though the thermostat wasn't changed. This is a direct response to the higher radiant temperature of the surfaces, which are now drawing away less body heat from the occupants. When cooling an uninsulated home, the opposite occurs--walls become hot from outside air and radiate heat to the inside, making people feel warm even while the air conditioner bathes them with cool air.

Windows are a special case for radiant temperatures. Single-glazed windows are much colder than walls; on a cold winter day frost often forms on the inside. This means that a house with many windows can still feel chilly, even after walls and ceilings have been insulated. Double, or triple-glazed windows (especially those with low-emissivity coatings) will help alleviate the problem while cutting a major heat loss path to a fraction.

The key to providing thermal comfort throughout the home is knowing the basic principles of heat flow: where it comes from and how it moves. A home is warmed by the sun and the heating system, and by heat given off from appliances, lighting, people, and pets. In winter it's important to know how these sources can work together most efficiently, while during the summer it is beneficial to determine how to reduce their impact.
 

Remodelers often insulate and weatherize exterior walls, while spending little time fixing interior leaks. When adding on to a home, remodelers should remember that the connecting points between the new and old section are common sources of air leakage, no matter how well-insulated and tightly-sealed the new area may be. This graphic illustrates some of the many air leakage pathways in a home. Note that many pathways do not pass through exterior walls.

I FEEL A DRAFT

This simple statement of thermal discomfort could have many explanations. These are frequently translated into an unwanted intrusion of cold air. It's usually possible to locate the path of this cold air, but it's much more challenging to find where and why warm air is leaving--it's also an excellent way to see why it's important to look at the house as a system.

Differences in air pressure play a surprisingly important role in air movement in a home. Fans from furnaces, air conditioners, and ventilation units all move air by creating pressure differences. Those are reasonably obvious and controllable. But the stack effect--caused by hot air rising--can create high pressures above and low pressures below, pushing and pulling air to unexpected destinations.

Drafts can also occur if the furnace or water heater is drawing combustion air from heated space, causing cold air to be sucked in through cracks and piping chases all over the house. A remodeled room with new utility and plumbing penetrations might become the easiest path for cold air to enter. This could explain why a long-awaited new bathroom was uncomfortable from its very first day. Who would have expected the water heater to be responsible for the drafts?

Similar problems are caused by poorly connected ducts, improperly designed wood stoves, and practically any combustion device. A strategically placed door or a simple duct repair can sometimes provide comfort benefits--in addition to energy savings--equal to a major insulation retrofit. Recent studies show that sealing ducts in the basement alone saves an estimated average of 10% in energy use, but can go over 20% in many cases.

Uncomfortable drafts can also be caused by the heating or cooling system rather than leaks in the building envelope. Most heat pumps are known for delivering cold air during the winter because they produce cooler air than say, a gas-fired furnace, and are designed so they move air through the ducts much faster causing the air to also feel cooler. Alternatively, drafts may be caused by a faulty fan switch in a furnace, resulting in air being circulated long after the furnace burner has switched off. The point here is that, unless you treat the house as an integrated system, many of the opportunities to save energy and improve thermal comfort will be overlooked or, worse, treated incorrectly.

The stack effect occurs when the outside air temperature is cooler than the inside temperature, and the warmer, lighter interior air rises, creating higher pressure in the upper part of the house than the lower part. The result is that air is drawn in through holes at the bottom of the house and pushed out through holes at the top. Around the middle of the house, the air pressure inside is close to or the same as outside (the neutral pressure plane), so the leakage is minimal, even if holes exist. The stack effect is only one of the factors that determine house pressure-others include wind, combustion appliances, and forced air distribution systems.

THE ELUSIVE THERMAL BOUNDARY

The thermal boundary of a home seems like a simple thing to identify; it's where the insulation is (or should be) located. However, in practice, the boundary is difficult to identify and may change dramatically due to remodeling or construction of additions.

Determining the exact location of the thermal boundary is especially complicated in houses with kneewalls, for example, or with junctures between the living space and porches and garages. To be effective, the boundary must be continuous and completely enclose the living space, so energy is not used to condition spaces outside of it.

Basements in many homes are particularly difficult to pin down because they become partially conditioned by heating and cooling equipment located there and by conditioned air leaking into the basement from the living space above. When this is the case, it is often best to include the basement in the thermal boundary, which also takes advantage of the insulating value of the ground surrounding the basement. The basement should then be insulated at its exterior walls and floor, rather than between the basement and the floor above.

A faulty remodel can create leaks in the thermal boundary equivalent to leaving a window open day and night. To be sure a new room doesn't become an energy drain, contractors can determine leakage with tools such as a blower door.(See Guide to `Total Comfort' Training, p 31.)

Determining the location of the thermal boundary of a home is the first step to treating the house as a system. A remodel can change the thermal boundary-an obvious example would be converting an attic that was once outside the thermal boundary into a living space. Basements are often included in the thermal boundary (even when they are not intentionally conditioned) because waste heat is often generated by equipment located there, ducts often run through them, and.it can be difficult to seal between the basement and floor above.

APPLIANCES AND FUEL CHOICE-NOW MAY BE THE TIME TO SWITCH

One of the most perplexing decisions is the choice of fuels for major appliances, that is, the furnace, water heater, clothes dryer, and stove. Gas-fired appliances are generally cheaper to operate than their electric counterparts but cost more to install. The lower first-cost of electric appliances causes many people to select them, so houses are often saddled with expensive electric water heaters and clothes dryers, even though gas service is available.

A remodel is a perfect time to establish a less expensive mix of fuels. The right choice of appliances (and the fuel to operate them) is based on more than just economics and availability. Some people don't feel safe with natural gas, yet others insist on it for cooking or rapid recovery capability in water heating. These are all legitimate considerations; however, one should begin by establishing the most economically attractive combination, and then superimpose individual preferences.i

Additions to houses typically rely on electric resistance heating or separate air conditioning rather than extensions from the existing system. Contractors may argue that this is necessary because the house's existing furnace or air conditioner lacks the capacity to serve another room or the extension is too expensive. These arguments deserve scrutiny, especially from the whole-building perspective.

Electric resistance heating is cheap and simple to install, making it attractive in many remodeling plans. Unfortunately, electric resistance heating can be very expensive to operate in cold climates or for long periods. The practical problems associated with installing a heating system in a limited or awkward space may require this solution. However, to ensure reasonable operating costs, insulation and other energy-saving measures should exceed code requirements, if the codes did not take this heating application into consideration.

Many homes have oversized central systems that have been running inefficiently since they were installed. So adding space may actually help correct this problem. In other cases, a tune-up may be all that's in order. If insufficient capacity is the problem, it might be addressed by insulating other parts of the house. This will make those areas more comfortable while providing sufficient capacity for the addition. For air conditioning, better shading of windows (or even low-emissivity windows) and duct repairs may free up lots of cooling capacity. Taking steps to reduce the thermal losses or loads elsewhere may not be the cheapest option, yet it offers many benefits in thermal control, comfort, and reduced bills.

WHEN IT COMES TO LIGHT

Virtually every remodel modifies some aspect of lighting and opens many opportunities for efficiency improvements. Efficient lighting does not necessarily mean more fluorescents; instead it means using light--from all sources--more cleverly. It is a mistake to consider lighting as purely electrical when so much illumination is natural. Windows, and the landscaping around a house, can have an enormous effect on the house's brightness, spaciousness, and overall character. So lighting is more than a choice of fixtures and bulbs; it includes windows, skylights, curtains, awnings, and landscaping.

Lighting sets the mood for a house and is also something quite personal. It is easy for a remodel to dramatically change the lighting in a room and the way people use it, making the remodeled area stand out from the rest of the home. Again, this is a good time to take a look at the whole house and its lighting needs. A typical house uses 6% to 20% of its electricity for lighting. Retrofitting one room may not amount to significant savings, but making some simple lighting efficiency adjustments throughout could reduce energy bills further while enhancing the overall appearance of the home.

Lighting can affect thermal comfort and heating and cooling bills as well. Installing new windows on the southfacing side and adding thermal mass--like laying terra cotta tiles--can be a relatively simple way to take advantage of solar heat while providing light at the same time. Southern exposure can be used to heat a home in almost any climate, and the use of longer eaves or awnings will keep the room bright, yet cool, in summertime.

Sealing the building envelope
isn't always easy.

HEALTH AND SAFETY BENEFITS

There are several other whole-house impacts of remodeling, and many affect energy use. One of the most insidious is moisture. The presence of excessive humidity is an indicator of several possible energy-related problems, from improper air conditioner sizing to a broken exhaust fan. High humidity and moisture condensation can lead to material damage and possibly even a range of health problems.

Pollution is another consideration. The air that brings cool relief from the central air conditioner to the bedroom may also carry radon that seeped in through leaky ducts in the dank crawlspace. Toxic fumes and air pollutants can enter through leaky ducts or passages in the building envelope.

Odors should not be a whole-house issue. But ventilation mistakes are made and the garlic in the kitchen may permeate the far bedroom. People respond by opening windows and increasing air infiltration far beyond that needed by a standard ventilation fan. This wastes heating and cooling energy.

Energy and noise can also be related. First there are the common complaints of noisy appliances, notably the dishwasher, refrigerator, furnace (and fan), and air conditioner. Attempting to deal with their noise may lead to inappropriate energy efficiency solutions, such as failing to provide combustion air to a furnace as a way to muffle it. Second, thermal insulation can provide (limited) sound insulation, especially against outside noise. Thus, dense-pack cellulose wall insulation and double-glazed windows may be installed primarily for sound protection and result in a pleasant drop in space-heating energy use.

STEP OUTSIDE BEFORE REMODELING

Future articles in this series will cover energy aspects of remodeling specific rooms and systems. The purpose of this article is to encourage a more global view.

Step outside the kitchen, bathroom, or basement, and try to consider the broader consequences of the remodel at the planning stage. It may result in a more energy efficient, comfortable, and safe home.

REMODELING REMEDIES FOR POLLUTANTS AND MOISTURE

Aside from improved comfort, one of the bonuses of remodeling can be improved indoor air quality. Often long-existing problems are identified and corrected during a renovation. Because the house is a system, altering one area can bring benefits to the whole house. But it also can spell danger; be alert to potential hazards. For health and safety reasons, it is a good idea to have air analysis and pressure testing done before and after remodeling.

As air moves in and through a house, it can carry with it pollutants from both indoors and outside. Volatile organic compounds, released from carpets, furniture, and building materials, along with radon, allergens, and other pollutants from outdoors, can be trapped inside if a home is not properly ventilated.

Other dangers exist when negative pressure is created around combustion appliances such as the furnace or water heater. This can cause poisonous flue gases which contain deadly carbon monoxide and oxides of nitrogen to backdraft into the home. Depressurized conditioned spaces also suck air into the home from outside, sometimes through such undesirable avenues as the fireplace chimney. Usually faulty exhaust systems and poorly sealed or disconnected ducts are to blame.

WET, WILD AND NOT SO WONDERFUL

Air movement also circulates moisture throughout the home. If it condenses on windows, it can cause sashes and sills to decay, but inside walls, it can do even worse (and hidden) structural damage. High relative humidity (above 70%) can feed the common allergens, mold and mildew, creating chronic health problems for occupants.

Energy-efficient homes need to be remodeled so they can breathe through controlled ventilation and/or construction that ensures condensation happens where it can safely drain or evaporate without causing problems.

In a heating climate, the moisture sources indoors can be just as big a problem as rain seeping in through faulty roofs or foundations. People's activities (cooking, bathing--even breathing) cause moisture to build up indoors if there is not sufficient ventilation.

Air sealing can help reduce cold spots, like window sills or corners, and stop moist air from seeping into the walls. Complete protection may mean installing a vapor barrier in the right place to control moisture condensing inside walls. In hot, humid climates, most of the moisture is coming in from the outside. An air conditioner or dehumidifier can reduce the humidity inside (although some high efficiency air conditioners reduce temperature without removing much moisture).

The series on energy-efficient remodeling is part of a project being funded by the Environmental Protection Agency and the Department of Energy.

 

Related Articles

Building Science Education in the Community College (Uniacke)
Building Tightness Guidelines: When Is a House Too Tight? (Tsongas)
Guidelines for Designing and Installing Tight Duct Systems (Stum)
Home Alone--Living Off the Grid (Casebolt)
Perry Bigelow: Energy Efficiency Maestro (Andrews)
Reducing the Embodied Energy of Buildings (Mumma)
Training Guide for 'Total Comfort' Professionals
Remodeling Kitchens: A Smorgasbord of Energy Savings (Sullivan)
Retrofitting Flooded Homes (Corbett and Everett)

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