Saving energy is the mantra of the "green movement"; unfortunately, there are some downsides to conserving as much energy as we can. One of those downsides can be poor indoor air quality.
In many buildings with inoperable windows, ventilation systems are turned down to reduce heating and cooling costs, resulting in higher indoor concentrations of contaminants. In order to meet government-mandated SEER requirements, some pieces of air conditioning equipment have blower motors that no longer have the capacity to push air through a MERV-8 filter, the minimum rating that ASHRAE recommends. Without efficient filtration, the system becomes contaminated with biodegradable dust that builds up on the cooling coil. Green then really means green, because microbial growth is inevitable.
Boilers and furnaces today are available with 94% or higher efficiency combustion, as compared to some of the clunkers of yesteryear that probably were not much more than 70% efficient. The temperature of the combustion gases coming out of the old clunkers might have been 400ºF or higher. The temperature of the combustion gases coming out of some high-efficiency, gas-fired equipment can be as low as 100ºF. Up to 50% of combustion gas consists of water vapor. Pure water vapor condenses at the same temperature at which water boils: 212ºF. To produce more heat, high-efficiency combustion equipment takes the heat (along with some water vapor) out of the combustion gases. The gases are so cool that further cooling results in condensation in the vent pipe. Most modern equipment is direct-vented out the side of a house, because if the equipment were vented into a chimney, the water would condense within the chimney, cause damage to the flue liner and minimize draft. Condensate lines and pumps are present on high-efficiency equipment in order to collect and discharge the condensate.
I was asked to investigate a home in which a high-efficiency, oil-fired Buderus boiler had just been installed. The homeowner had chemical sensitivities. The older heating system hadn't bothered her, but now she found the basement air noxious, even though she'd asked that the boiler be vented into the chimney. The temperature was about 20ºF on the day of my site visit, and there had been an overnight snowstorm. When I pulled up to the well-maintained home, I noticed that there was an exterior chimney, and the metal screen on the chimney cap was covered with ice. When the boiler turned on, the smoke consisted of steam that barely rose from the chimney. Even though the temperature of the flue gases had been raised through adjustments to the internal flue baffles, it was obvious that the combustion gases were still being excessively cooled because they were traveling through the cold vent pipe inside the ceramic flue liner. In the basement, a bucket full of water under a horizontal section of flue pipe at the chimney breach confirmed my suspicion that excessive condensation was occurring within the vent pipe. I never recommend direct venting for oil-fired combustion equipment because all homes are somewhat leaky and when the wind is blowing against the vent, the combustion gases infiltrate the house. Unfortunately in this case, the vent pipe in the exterior chimney was not insulated.
In addition, the vent-pipe test hole was open, and because there wasn't much draft, there was spillage at the hole. I borrowed a screw from the homeowner and placed it in the hole, and that stopped the spillage. The oil-service company recommended pouring vermiculite into the chimney flue to insulate the vent pipe. This should help as long as the insulation is installed without any voids. (I also suggested that the homeowner check to be sure that the vermiculite didn't come from the Libby Mine in Montana, which supplied asbestos-contaminated vermiculate for attic insulation.)
The odor that bothered the homeowner the most was the smell of oil. When I opened the door to the basement, I could smell fuel oil. The oil tank was a newer-style, double-walled (Roth) tank that had been in place for about three years. A TIFF 8800 combustible gas detector picked up a vapor near the ceiling of the basement, with higher concentrations at the top of the oil tank. At the corner of the tank was a small, clear plastic cap, attached to a long metal rod that penetrated into the tank between the inner plastic and outer metal liner. This device is designed to detect any oil leaking into the space between the tank and the outer liner. There is a plug at the bottom of the tube that swells with oil and that pushes a rod into the clear plastic cap. In this case, there must have been a small amount of oil between the inner plastic and outer metal liner, and the odor was escaping around the loose-fitting gasket. I recommended that the homeowner have the tank checked for oil in the interstitial space, and have the gasket caulked.
Home inspectors take note: High-efficiency, oil-fired combustion equipment should not be vented into an exterior chimney unless the vent pipe is insulated. Any direct-vented (sidewall) pipe should be high enough so that it won't be blocked by ice and snow (warn the homeowner not to shovel snow up over the vent termination). The dryer vent should not be located too close to the air intake, or lint may build up in the intake and foul the burner. Lastly, in high-efficiency heating equipment, the condensate is acidic enough to eat through copper piping. Some installers now are including neutralizers to eliminate the acidity; these neutralizers contain crushed limestone (calcium carbonate) and must be replaced periodically.
©2011 Jeffrey C. May. IAQ IQ 42, February/March newsletter reprinted with permission of Jeff May.If you would like to receive the bimonthly bulletin by e-mail, send a request to me, jeff@mayindoor air.com, and put "IAQ IQ Bulletin" in the subject line. May Indoor Air Investigations, LLC, Tyngsborough, MA 01879. Call 978-649-1055 and visit www.mayindoorair.com.