Myth-Busting:

Fireplaces

Many decorative fireplaces have come on the market with ecofriendly labeling.  They typically burn ethanol or bioethanol and claim the fuel is so clean-burning you don’t need a chimney.  A clean-burning fuel that provides a cozy source of heat without polluting indoor air and without you having to punch a hole in your home’s thermal envelope in the form of a chimney?  It sounds too good to be true.

In theory, ethanol and bioethanol fuels burn completely into carbon dioxide and water.  In practice, this is unlikely.  This is in part because the fuels used are generally not pure ethanol.  Nu-Flame fuel, for instance, contains bitter-tasting Bitrex as a safety additive to discourage children and pets from drinking it.  And according to the material safety data sheet (MSDS) for a fuel called Moda Flame, though it includes greater than 90% ethyl alcohol, it also includes undisclosed proprietary ingredients.

We were able to find two studies that examine this issue, one by Fraunhofer-Gesellschaft, a wood research organization, and the other by Laboratoire national de métrologie et d’essais (LNE).  Both studies found that when these fuels were burned, other gases such as carbon monoxide, benzene, nitrogen dioxide and formaldehyde were released.  To be clear, a wood-burning fireplace will also release toxic particles and gases, and so will candles or anything else you burn in your home.  Ethanol and bioethanol may very well be cleaner-burning than a traditional wood fireplace, but that doesn’t mean it’s a good idea to introduce even a reduced amount of pollutants into your living space.

Another consideration with this type of fireplace is that special care needs to be taken with regard to storing the fuel, and the spent containers are considered hazardous waste and must be disposed of appropriately.

Any type of fireplace within conditioned space should be sealed and have adequate combustion and ventilation air provided.  Better yet, if you really want a fireplace, keep it outside.

Spray-Foam Insulation

Spray foam in the attic keeps conditioned leaks from the heating/cooling system and ductwork inside the home 

For the past decade or so, polyurethane spray foam has become a popular choice for insulation in new homes and to improve energy efficiency in existing ones.  However, like any building product, its performance depends on proper use and installation.

There are two predominant types of polyurethane spray foam.

Closed-cell foam has a density of approximately two pounds per cubic foot and is considered vapor-impermeable.  (The blowing agent in closed-cell foams was traditionally hydrofluorocarbons, which have high global-warming potential, but manufacturers have now developed blowing agents with zero global-warming potential.)  Closed-cell foam has an R-value of about 6 per inch or higher.  It is more commonly used in colder climates where higher R-values are required, or where it can serve as a vapor retarder.

Open-cell foam has a nominal density of a half-pound per cubic foot and is vapor-permeable.  (It becomes slightly less vapor-permeable as its thickness increases.)  Open-cell foam generally uses water or carbon dioxide as a blowing agent, and its R-value ranges from 3.3 to 4 per inch depending on the product.  Due to its lower R-value, open-cell foam is commonly used in warmer climates where building codes permit lower R-values, and where there is less need for a vapor retarder.

Both types of foam are comprised of two components — isocyanate and polyol resin — and they cure via a chemical reaction that occurs when the components are applied with a spray gun.  This is an important point: A contractor applying spray foam is actually manufacturing a product on site. That means both the proportion and temperature of the two parts must be optimal for a good result and good thermal performance.  How the installer operates the spray gun can impact the quality of the job.  So can the temperature of the air or the temperature of the substrate to which the foam is applied, which should be above 40^oF.

There are also “green” or bio-based foams. These are open-cell foams in which a renewable substance (usually derived from soy beans, sugar cane, or castor oil) has replaced some portion of the resin.  Under U.S. Department of Agriculture guidelines, just 7% of spray foam needs to be made from a renewable product to be labeled as bio-based.

Given Austin’s relatively mild climate, spray foam has only a marginal thermal advantage over other types of insulation.  It does, however, have two other advantages.

First, using spray foam can result in a house that has less infiltration of hot, humid air in the summer and cold air in the winter.  Spray-foam insulation can help create a tighter structure, reducing this infiltration and attendant energy loss.  Though a very tight house will need some type of mechanical ventilation to provide fresh air to the occupants, controlled ventilation is far preferable to uncontrolled infiltration.

Second, using spray foam makes it easier to locate the home’s heating and cooling system in the attic without severely compromising energy efficiency.  Many homes in Austin have their air conditioning systems and ductwork in the attic, which is the hottest part of the house in summer and coldest in winter.  If that attic is vented, conditioned air leaking from the system will be lost, resulting in wasted energy and less comfort for the occupants.  Applying foam to the roof decking and sealing the attic, attic temperatures can be moderated and energy loss is greatly reduced.

Not all homes are suitable for spray-foam insulation.  While new homes can be designed to take advantage of foam’s qualities, some existing homes may not be good candidates.  Homes with gas appliances (such as the furnace and/or water heater) in the attic, or with gas appliances that draw combustion air from the attic, can become dangerous if the attic is sealed with foam.  (Closed or sealed-combustion appliances do not present this risk.)  And homes with older windows that are leaky and inefficient may not see much of an improvement in overall efficiency from foam.

Spray-foam insulation is more expensive than fiberglass or cellulose insulation.  But if your budget precludes using foam throughout the exterior of the house, don’t abandon it completely.  Because Austin has a mild climate, walls that are insulated with fiberglass or cellulose insulation and are sealed can perform quite well.  You can then use spray foam to seal the attic, thereby improving the performance of the heating and cooling system if it’s located there.  You can also skim-coat the inside of the exterior sheathing with foam and fill the remainder with fiberglass, a technique known as “flash and batt.”

Excessive humidity should be avoided in attics sealed with foam.  Moisture in the form of water vapor can come from an attic that is not completely sealed, or from humid air leaking from the living space into the attic.  Because open-cell foam is permeable to water vapor, moisture can be driven through the foam up to the roof decking, where it can condense into liquid water, especially at night.  (Radiative cooling can lower the temperature of the roof to below the dew point.) If some or all of the heating and cooling system is located in the attic, incidental leakage of conditioned air from the system will help to control humidity there to some degree.  Moisture issues pose more of a problem further north or in areas more humid than Austin, but any risk can be minimized by careful attention to detail and good workmanship.

When considering spray-foam insulation for your home, choosing a competent contractor is critical.  (Despite manufacturers’ claims, there are only minor differences among brands.) The technicians applying the foam should be trained and certified to install that particular type of foam. Ask the contractor for references or try to visit foam jobs recently completed.  Instead of going with the lowest bid, go with the contractor that you feel will do the job right. If the foam is being applied in a house you are living in, plan on vacating the house for at least three days after the foam is installed, and get detailed information on how the house will be ventilated afterwards.

Keep in mind that spray foams are considered plastics by the International Residential Code, so they need to be covered or protected depending on where they are installed.  In almost every case, open-cell foam must be separated from occupants by a thermal barrier (usually half-inch gypsum wallboard).  In some locations, they may have to be covered by an ignition barrier or a coating that has been tested and approved for that particular foam.  Don’t rely only on what a salesman or contractor tells you.  Obtain safety information from the manufacturer and download the most recent report for the product from the ICC Evaluation Service Web site (http://www.icc-es.org/).  They have detailed information on how each type of foam should be installed and what treatment may be required.

Spray foam is like any other building material.  Being aware of its strengths and limitations will help you avoid mistakes and ensure that it delivers improved energy efficiency and comfort.

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