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#AskEnergySaver: Weatherization

November 25, 2014 - 12:23pm


This month our experts answered your #AskEnergySaver questions on weatherization. | Image courtesy of Sarah Gerrity, Energy Department.

This month our experts answered your #AskEnergySaver questions on weatherization. | Image courtesy of Sarah Gerrity, Energy Department.

To help you save money by saving energy, we launched #AskEnergySaver -- an online series that gives you access to some of the Energy Department’s home energy efficiency experts. During 2014, experts from the Department and our National Labs are answering your energy-saving questions and sharing their advice on ways to improve your home’s comfort.

Home heating and cooling account for about 48 percent of the average homeowner’s utility bill. As the weather gets colder, it’s important to weatherize your home in order to save money while staying cozy. And while we have lots of great tips for saving on heating and cooling, we know there are always more questions to be answered.

This month we asked you to share your questions about weatherization. To answer them we turned to Ely Jacobsohn, Program Manager of Home Performance with ENERGY STAR in the Department’s Buildings Technology office.

1. How do I determine if indeed I need to install ventilation of the attic?

-- from Bernie via email

Attic ventilation serves multiple purposes. It can assist in removing excess heat from the attic in the summer and excess moisture in the winter. However, in many homes, attic ventilation can also draw warm, moist air from the living space into the attic in the winter, contributing to problems like ice dams and moisture condensation on the underside of the roof. In cooling season, attic ventilation can similarly draw cooled air out of the house, resulting in wasted energy.

The best approach is to ensure that any connections where air might migrate from the living space into the attic are sealed and insulate the attic floor to the minimum levels recommended by the Energy Department and the Environmental Protection Agency for your climate zone. The amount of ventilation required depends on your local codes and is typically determined using a calculation based on the square footage of the attic space.

It is also important to check on the recommendations of your roof shingle manufacturer, to ensure that the all warranty requirements have been met. Keep in mind that energy, air and moisture movement through a home is a complex system and every home is different. Your house might behave differently from your neighbors’ homes. A home performance contractor can help you determine the best approach for your home using an analytical approach, while taking requirements for codes and warranties into account.

2. I have a very old house, and need to re-insulate. Should I vacuum up the old insulation or can I put new fiberglass insulation right over it? What would be the best thickness & type for efficiency?

-- from Lori via email

Given the age of your home and the description of the insulation, it sounds like you most likely have rock wool in your attic. This is a mineral product akin to fiberglass but often comprised of fibers that can be extremely sharp and scratchy, causing skin irritation if handled, so make sure that anyone working in the attic is fully protected with goggles, coveralls, respirators and good gloves. Rock wool can also be much heavier than fiberglass or cellulose, which could make it difficult to “vacuum” out of your attic. It doesn’t hurt anything to leave it in place and insulate over it.

Recommended minimum insulation levels vary by climate zone and can be found here. Check the specifications for the particular product and brand of insulation you choose to use to determine if the insulation has any potential pest retardant qualities. Cellulose insulation comes pretreated with a fire retardant, which typically consists of ammonium sulfate or boric acid. Boric acid is also commonly used as an insect repellant, and may assist in deterring certain types of insects, but the levels contained within cellulose are not tested and/or sold with any specific claim for performance as a pest repellant.

Regardless of the product you choose, it is advisable to ensure that you have no active knob-and-tube wiring before you add more insulation. Check with your local code official to be sure that your contractor follows the correct procedures for this.

Finally, to control heat loss and reduce the chances of moisture condensing on the underside of your roof, it is also important to get the attic “air sealed” prior to adding new insulation. If you add insulation without air sealing, the wintertime temperature of the roof surface will be colder than it was previously, creating an ideal place for moisture migrating from the living space to condense. This is controlled by sealing openings where warm, moist air from the living space might make its way into the attic -- like the tops of walls and places where plumbing, chimneys and ducts go through the ceiling. A home performance contractor can identify where these leakage paths are and seal them for you. A blower door test can help verify that the air leakage has been controlled so insulation can then be added.

3. Can you tell me what kind of vendor I should seek in order to have my windows & doors caulked?

-- from BSure2 via email

Air that leaks through your home's envelope -- the outer walls, windows, doors, and other openings -- wastes a lot of energy and increases your utility costs. A well-sealed envelope, coupled with the right amount of insulation, can make a real difference on your utility bills and your home’s comfort.

The best way to ensure that the work is done properly is to enlist the services of a qualified professional. A professional can determine what work needs to be done and which product would best serve your needs. You can find a contractor from the Department of Energy’s Home Performance with ENERGY STAR program. Home Performance with ENERGY STAR contractors evaluate your house as a system and recommend the best approach for your unique situation.

You can also look into local incentives to help offset the cost of the project. In addition to the Find a Program link for Home Performance with ENERGY STAR, you can search the rebates section for energy efficiency incentives. The Weatherization Assistance Program is also available to income-qualified homeowners. This program is overseen by the Department of Energy, administered by the states, and provides grants to provide weatherization services to those in need.

4. What temperature should I keep my thermostat at to save energy?

-- from Sharon via email

The short answer to your question is whatever makes you most comfortable.

If you have a well-insulated home with minimal air leaks and energy efficient heating and cooling equipment, it will be easier for your home to maintain the temperature of your choosing while still operating efficiently. If you are looking for ways to further reduce your energy bills by adjusting the temperature at night or when you are out of the house, then the “correct” set-back temperature depends on the type of heating equipment you have. There are several factors to consider including the type of thermostat you have and whether you use forced warm air, hot water or steam to heat your home.

In general, forced warm air systems recover quickly from temperature setbacks, making it possible to turn the temperature up and down multiple times a day if your lifestyle allows for that. A hot water system, on the other hand can take anywhere from several minutes to several hours to recover from a temperature setback, depending on how far back you turn the temperature and for how long. This is due to the fact that while the boiler water may maintain its temperature, it still takes a lot of energy to re-heat the water in the distribution pipes if it has gone cold. Steam radiators can be controlled if the system is balanced and has properly installed thermostatic radiator valves and will recover quickly from temperature setbacks on a room-by-room basis.

The thermostat you use is also important. There are many digital thermostats available on the market today with features that allow for temperature setbacks to be programmed to automatically occur according to your schedule on a daily and weekly basis. There are also smart thermostats which learn from your habits and try to predict where you will want the temperature setting at any given time of day. If you have a heat pump and you want to set the temperature back, it is important to make sure that the thermostat you use is designed for a two-stage “ramped recovery” which helps control getting the house back up to temperature without forcing the secondary (“emergency”) heat source to kick on.

For some systems, the best course of action may be to simply select a single temperature setting to be maintained with no regular setback as the cost of recovering from the setback could outweigh the benefits of turning the temperature back in the first place.

5. Should I insulate the ductwork in the ceiling of my basement? If so--what product should I use?  

-- from Brenda via email

The answer to your question depends on a few factors. First, it is important to have the ducts sealed before you insulate them. Second, the cost-effectiveness of insulating the ducts depends on whether or not you use the ducts for heating (as opposed to just cooling) and how cold it gets in your basement. If the temperature in your basement never drops below 50-55 degrees, there might be better places to in your home to invest in energy saving improvements. Another reason to insulate the ducts is if they are used for cooling and tend to “sweat” in the summer. Insulating cooling ducts in humid locations can help prevent condensation from forming.

After taking those considerations into account, this is a project best handled by a professional home performance contractor who can diagnose your situation and recommend the best course of action.

For more ways to save energy at home, check out Energy Saver.