Radiant Barriers – Good for Energy Savings/Bad for Fire Safety

They can cool the attic … but at what risk to the structure and the occupants?  Could radiant barriers represent a potential for harm?

Read the McDowell Owens Engineering Inc. white paper as to how “The physical and electrical properties of these materials are such that they introduce new and very serious dangers of ignition and fire.”  

The link that I had used for years to the original McDowell Owens Engineering Inc. report is no longer operating; however, you can find a pdf copy of the report by clicking here.

The summary of the McDowell Owens Engineering study is, as follows:

“1. Standard installation methods for roof sheathing with integrated radiant barrier are such that the end result is an overall environment where all of the radiant barrier material and virtually everything metal on and around the roof are electrically connected.

“2. In most cases, something in that environment is connected to earth ground. If anything in the roof environment becomes electrically energized (by lightning or any other common source) there is a high probability the current will pass through the barrier material at some point on the way to earth ground.

“3. The physical and electrical properties of reflective radiant barrier materials which we tested are such that the material in a structure provides two new and unique hazards relative to fire causation.

(a) When energized by an electrical current the material readily generates temperatures sufficient to ignite MANY materials.

(b) The barrier material itself readily serves as the first ignited material.”

If you are considering radiant barriers as an energy efficiency upgrade … if you reside in a home with radiant barriers that are installed … if you are considering a recommendation by an energy auditor or other entity to install them … read this report, first.

Energy Efficiency and Your Water Heater (Part Two)

Conventional gas water heaters present an additional challenge to the home owner improving the energy efficiency of their water heater.  In addition to the energy loss through demand, standby and distribution (as previously discussed), the conventional gas water heater will waste a greater percentage of energy than electrical water heaters due to the design of the burner and ventilation system.

The wasted energy specific to gas and oil water heaters are:  excess air, dilution air and off-cycle air circulation.

Excess Air

Approximately 15 cubic feet of air is required to efficiently burn one cubic foot of gas.  Wasted heat and combustion by-products are carried by air through the chimney and are not heating water.  Some of this waste cannot be avoided, but the more excess air that flows through the burner the more energy is wasted.

Dilution Air

Dilution air is air from within the room that enters the flue at the draft diverter during combustion to assist in providing the draft needed to carry the dangerous combustion by-products to the outdoors.  Some or all of this dilution air is air that has been heated or cooled from the home.

Off-Cycle Air Circulation

Surrounding indoor air circulates through the burner and flue, carrying the heat away from the water (and conditioned air away from the home) and up the chimney.

There are improved gas and oil water heaters that reduce these losses that are directly related to ventilation by restricting the air that flows through the flue and chimney.  Some designes have eliminated the draft diverter.

By restricting the air flow through the flue and chimney, air circulation carrying the heat away from the tank has been reduced.

None of these are modifications that the home owner should do on their own since proper drafting through the flue and chimney are necessary to ensure that the dangerous by-products and gases produced during the combustion process are safely vented to the outdoors.

Since gas is a less expensive energy resource than electricity, many home owners will want to find the way to efficiently use it as opposed to replacing their gas appliances with those using more costly electricity.  The professional who conducts the diagnostic home performance evaluation will assist the home owner in locating a qualified contractor who can safely affect these changes.

Mobile Homes: Most Serious Air-Leakage Sites

Improving the comfort and energy efficiency of a mobile home (now called “manufactured home”) can present special challenges.  Keeping the conditioned air inside the home and the unconditioned air on the outside can be particularly difficult, due to the home’s design for intended mobility.

Prior to attempting to remedy air-leakage, owners and occupants of mobile homes should ensure that a diagnostic analysis is performed before and after the air sealing efforts to ensure that there is safe levels of air for proper ventilation and to prevent the growth of mold.

The most serious areas for air leakage in mobile homes are:

1.  Water heater closets with exterior doors.

2.  Plumbing penetrations in floors, walls and ceilings.

3.  Torn or missing underbelly.

4.  The joints between the halves of doublewide mobile homes.

5.  Joints between the main dwelling and any additions that might have been added.

6.  Large gaps around chimneys (furnace and water heater).

7.  Deteriorated floors in water heater compartments.

8.  Gaps around electrical service panels, fans and light fixtures.

9.  Jalousie windows.

10.  Leaking crossover air ducts.

%d bloggers like this: