Monday, January 14, 2008

Four Step Weatherization Guide

The (Re)Weatherization Sequence

Step 1: House Air Tightening and Systems Checkups

  1. Duct sealing and insulation. If you have forced air ducts in your house, have them tested and sealed by a state certified duct-sealing contractor. Ducts should only be sealed with duct mastic, never with tape (Home Depot often carries duct mastic). While the duct sealers have their blower door set up, find out how leaky your house is, and where the leaks are. Consider installing additional return registers or pressure bypasses if you have a single return forced air duct system. After they are sealed, insulate the ducts to at least R11 (R25 is better), even if they already had an inch or two of insulation. If the system has air conditioning, put a vapor barrier on the outside of the duct insulation.

  2. Air seal the house. Use caulking, spray foam, plywood, sheet metal, and weather-stripping, to seal places where air moves inside from outside, and also vertically through the house. Seal around windows and doors, seal the gaps around plumbing, wiring, mechanical, and chimney from underneath the house and from the attic. Sweep attic insulation aside, clean and foam the cracks where interior and exterior walls meet the ceiling. Cover the holes where plumbing drops through the floor under the bathtub and shower. Install outlet and switch cover plate gaskets. Remember that fiberglass does not stop airflow! A dense cellulose pack will reduce infiltration. Using a blower door makes airsealing faster and more effective.

    WARNING! Steps 1A and 1B. If you have any combustion appliances in your home, equipment that burns wood, pellets, gas, propane, oil, or kerosene, such as fireplace, woodstove, space heater, gas log, water heater, furnace, range or oven, etc., it is critical that you have a trained contractor perform a Worst Case Depressurization Test, or Combustion Appliance Zone Pressure Test to verify that the changes in the house have not created combustion gas backdrafting hazards. Combustion gas backdrafting can be fatal or cause long term health damage. An state certified duct sealing contractor can perform this test for you, and show you how to correct any hazards.

  3. Ventilation and other systems checks. A blower door test will demonstrate how tight your house actually is, and where you may have missed a leak or two while airsealing. If your house tests below .35 air changes per hour (ACH), you should install fresh air vents as well as a high quality spot ventilation bathroom fan, or, ideally, an air-to-air heat exchanger to help maintain good indoor air quality. Install quiet bath fans and make sure they are properly vented outside through the roof or wall (see the Energy Outlet handout on bath fans). Install a range hood or verify that the existing fan vents to the outside in galvanized steel parts only. Make sure the dryer vent goes completely outside, in metal duct, not plastic. Now is the time to replace knob and tube wiring, add a grounding conductor, or otherwise upgrade your electrical system. Add phone or data lines. Check for adequate attic and crawlspace ventilation. Complete any structural repairs. Make sure water pipes are freeze-protected. Check for signs of water leakage around flashing at windows, doors, and dormers. Dry out that wet crawlspace with drains or a pump, and install a 6 mil plastic ground sheet.

Step 2: Insulation

Insulate the ceilings, floors, and walls of your house. Do uninsulated or low R-value areas first. Ultimately, you want all exterior components of the house fully insulated. Many houses are underinsulated, even if they have been “weatherized” in the past. Some contractors will attempt to persuade you that an attainable R-value is not “cost-effective”. This assertion is based on an obsolete set of assumptions.

The Insulation Rule of Thumb: There is no such thing as too much insulation! There may be technical or financial obstacles to installing more insulation, but there is no such thing as too much.

If you add insulation to the exterior (cool) side of a building surface, be sure unfaced insulation is used, so that the one and only vapor barrier remains next to the warm surface at the interior side of the building component. If the vapor barrier has been installed to the cold side, turn the insulation over or peel or slash the barrier. Often floor framing cavities are not completely filled, and can be added to. Additional floor insulation can be installed with wood furring or 16D nails that add depth to the framing, or with rigid foam sheets. Don’t forget to insulate cantilevered floors, or the rim joists, especially on multi-story homes. Vaulted ceilings often require rigid foam sheet insulation or added interior framing for fiberglass batts. Even insulated exterior walls can be improved by installing 1"-2" rigid foam sheets inside and re-sheetrocking. Use extruded polystyrene or polyiso foam, and foam and tape the joints for an excellent vapor barrier. Consult with the Energy Outlet for detailed insulation project assistance.

Step 3: Windows

Install new windows. Windows are last on the building shell list because they offer the least bang for the buck of any weatherization measure, and are usually the lowest priority in terms of actual heat loss. Exceptions to this rule include jalousie windows or windows that need expensive repairs. When you buy windows, specify these options: warm-edge glazing spacer, Low E glass (set up for a heating climate), krypton or argon gas fill. These glazing options will get you a window with a U-value close to .30 (lower U is better). Optimize the characteristics of the Low E coating by using soft-coat Low E on north and west facing windows, and hardcoat Low E on south and east facing windows. The choice of frame material is purely an aesthetic and cost question, since vinyl, composite, fiberglass, and wood frames perform about the same thermally. Existing wood frame windows can often be retrofitted with double-glazed replacement sash that come with new insert jambs, available from Kolbe and Kolbe, Marvin, and Pella. Old double-hung wood windows with weights can be replaced with larger windows if you extend the new windows into the area formerly taken up by the weight pockets. Excessively large window areas, especially if they don’t face south, should be sized down when windows are replaced. You may need overhangs, awnings, or rollup shades to keep the summer sun out. Rigid foam panels can be used as very effective interior nighttime window insulation.

Step 4: Heating Appliances

Install high efficiency home heating and water heating equipment, and maintain it properly.

Install the best Energy Star equipment, and you may qualify for an state income tax credit.

  1. Sizing. As you tighten and insulate your home, the amount of heat your house requires to stay comfortable will decrease. Make sure your heating contractor does an ACCA Manual J Heat Loss Calculation to establish a heating and cooling load for your house as it will be when weatherization is complete. Size all new equipment to the new reduced heating and cooling loads.
  2. Efficiency and Safety. Most pre-1990 propane, natural gas, or oil furnaces operate at less than 80% combustion efficiency, some as low as 60%! You can install a 90%+ efficient furnace or boiler and reduce your heating bill by an amount corresponding to the difference in efficiency between new and old heating units.

    WARNING! Atmospheric draft combustion appliances nearly always present the risk of backdrafting, especially if they are located indoors! Avoid using atmospheric draft appliances. Fan-forced or sealed combustion heating appliances are always safer and more efficient, and are essential for indoor installations. And, despite the fact that they are may be legal in your state, “Unvented” heating appliances should never be used indoors under any circumstances!!! (Unheated garages are not usually considered “indoors”)

    Heat pumps. Heat pumps allow you to improve the efficiency of an electric heating system, are available as ground source or air source models. Ground source heat pumps are amazingly efficient, but expensive to install. Ground source well systems are preferred over field systems. Energy Star air source heat pumps have an HSPF of at least 7.6, and SEER of at least 12. Air source heat pumps are available for ducted or ductless systems. Split ductless heat pump systems avoid expensive duct installation and heat loss, and are easier to retrofit.

Check with your local government for Energy Tax Credits and Business Energy Loans for installing high efficiency and renewable energy building systems. Your heating energy supplier will provide an energy audit of your home, and some incentives also.

1 comment:

mikesac said...

All are great tips. We usually do our air duct cleaning to do our part in the energy conservation movement. It makes a pretty big difference.