Gas furnace not sealed to the platform
Q: Before buying my home, I hired a home inspector. He said everything was OK with the forced air furnace. After closing escrow, I had the gas company turn on the service and light all of the pilots. This should have been a routine process, but the gas man red-tagged the heater. He said the base of the furnace should be sealed to the wooden platform. He explained something about "combustion air" in the closet and other technical jargon that went right over my head. Could you please explain why the base of a furnace should be sealed to the platform?
A: When gas companies activate service, they routinely inspect for safety-related violations, including (but not limited to) gas leaks, exhaust venting, clearances to combustible materials, physical damage and compliance with combustion air requirements.
Combustion air standards are so critical to personal safety that the Uniform Mechanical Code devotes an entire chapter to the subject. Basically, combustion air is the oxygen supply to the gas burner. The requirements in this regard can be broken down into three basic issues:
• A gas burner must have an air supply sufficient to enable total combustion of the fuel being burned.
• The air supply should be drawn from a location that will not create a hazard to occupants. For example, forced air furnaces should not draw combustion air from a bedroom.
• When gas-burning fixtures are installed in confined spaces, such as a closet, it is possible for exhaust fumes to mix with the combustion air supply. When this happens, contaminated air can be circulated into the home, exposing occupants to deadly carbon monoxide.
A simple way to isolate exhaust fumes from the circulating air is to seal the base of the furnace to the platform, as your gas man recommended. If the base of the furnace is not sealed, low air pressure inside the blower compartment can draw combustion air through unsealed gaps. If the air is contaminated with exhaust, this can be blown into the rooms of the home and breathed by occupants. Fortunately, a mere bead of caulk around the base of the furnace can eliminate this problem.
Q: The home inspector who checked my house found deteriorated fiberglass insulation in the crawl space under the building. Some of the insulation is hanging down, and some of it is shredded. What causes old fiberglass insulation to deteriorate in this way?
A: Fiberglass insulation does not deteriorate with age. Damage is the result of some kind of mishandling, usually by wild animals such as rats, raccoons, opossums, etc., or domestic creatures of the canine or feline variety.
If the insulation under your home is damaged, check the vent screens around the building. Most likely, you will find at least one that has been torn or is missing. Replacement screens, consisting of quarter inch hardware cloth, can be purchased from most hardware stores.
Barring animals from your crawl space is part of routine home maintenance, not only to protect the insulation, but to keep the subarea from being used as a litter box.
• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.
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