For best performance, we recommend that you replace the Water
Panel evaporator in your Aprilaire humidifier at least annually with
the exception of Models 400 and 400M which should be changed at
least twice per heating season.

The “Change Water Panel” indicator light (Digital Control only) will blink
when it is time to change yourWater Panel. See individual model instructions
for additional maintenance.

To purchase a new Water Panel:

• Visit estore.aprilaire.com
• Call the installer of your Aprilaire humidifier.
This information is often found on your equipment.
• Call your heating and air conditioning dealer.
• Use our “Dealer Locator” at: www.aprilaire.com
• Purchase only Genuine Aprilaire Water Panels to maintain performance.

If your humidifier is equipped with a Digital Humidifier Control with Water
Panel change indicator, after replacing the Water Panel, turn the control
knob to the “Test/Reset” position until the “Humidifier On” light blinks to
reset its timer. (Blower must be operating and HVAC calling for heat.) Be sure
to turn the control knob back to it’s original setting. If the “Humidifier On”
light continues to blink, your humidifier is in Test mode. DO NOT LEAVE THE
CONTROL IN TEST MODE OR HUMIDIFIER WILL NOT OPERATE.

Also review the periodic preventavtive maintenance in the owners manual.

Harmful effects of molds

The type and severity of health effects that result from molds exposure is widely variable among different locations, from person to person and over time.

Although difficult to predict, exposure to molds growing indoors is most often associated with the following allergy symptoms:

Long-term exposure to indoor molds is certainly unhealthy to anyone, but some groups will develop more severe symptoms sooner than others, including:

• Infants and children
• Elderly people
• Individuals with respiratory conditions, allergies and/or asthma
• Immunocompromised patients

Some indoor molds are capable of producing extremely potent toxins (mycotoxins) that are lipid-soluble and readily absorbed by the intestinal lining, airways, and skin. These agents, usually contained in the fungal spores, have toxic effects ranging from short-term irritation to immunosuppression and cancer. (Photo: Mold growing behind wallpaper)

More severe symptoms that could result from continuous human exposure to indoor mycotoxigenic molds include:

• Cancer (aflatoxin best characterized as potential human carcinogen)
• Hypersensitivity pneumonitis/pulmonary fibrosis
• Pulmonary injury/hemosiderosis (bleeding)
• Neurotoxicity
• Hematologic and immunologic disorders
• Hepatic, endocrine and/or renal toxicities
• Pregnancy, gastrointestinal and/or cardiac conditions

It is important to notice that the clinical relevance of mycotoxins under realistic airborne exposure levels is not fully established. Further, some or much of the supporting evidence for these other health effects is based on case studies rather than controlled studies, studies that have not yet been reproduced or involve symptoms that are subjective.
(Photo: Black mold spores micrography)

Among the indoor mycotoxin-producing species of molds are Fusarium, Trichoderma, and one that, although less commonly isolated, became notorious during the past decade, Stachybotrys atra (aka S. chartarum, black mold). Between 1993 and 1994, there was an unusual outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio, where one kid died. Researchers found that the kids’ homes had previously sustained water damage that resulted in molds contamination, and the quantity of molds, including S. chartarum, was higher in the homes of infants with pulmonary hemorrhage than in those of controls. (Photo: Stachybotrys growing on Potato Dextrose Agar (PDA))

It was this Cleveland event that initiated the headline news of Stachybotrys. The American Academy of Pediatrics produced guidelines in the wake of the outbreak. Other incidents involving kids in Stachybotrys-contaminated water-damaged school buildings have captured headlines as well, with children becoming symptom-free after being removed from those environments.
Article from the Fargo Forum newspaper, North Dakota (5/1/1997)

The role of S. chartarum in pulmonary hemorrhage in the Cleveland incident and in human health in the indoor environment is not clear though. There is not enough evidence to prove a solid causal relationship between S. chartarum and these health problems. Actually, in 2000 the CDC released two reports critical of the study conducted in Cleveland and concluded that the association between S. chartarum and acute pulmonary hemorrhage was not proven.

While case studies certainly indicate the possibility or even the plausibility of an effect from molds exposure, such studies by their nature cannot address whether the effect is common or widespread among building occupants. Results from studies that have not been reproduced may be spurious or have yet to be confirmed by well-designed follow up studies. (Photo: Moldy humid walls in a closet space)

In large epidemiologic studies, general symptoms have been associated with moisture damaged and presumably moldy buildings. Many of the reported symptoms are subjective and difficult to quantify. Results are confounded by the fact that the association is general, and mold is not the only possible cause of the symptoms. Neither condition proves that mold is NOT a cause.

In any case, molds growth in the indoor environment should be considered unacceptable from the perspectives of potential adverse health effects and building performance.

Dose-response

There is almost a complete lack of information on specific human responses to well-defined exposures to molds contaminants. There is currently no proven method to measure the type or amount of mold that a person is exposed to, and common symptoms associated with molds exposure are non-specific, aggravated by the facts that molds are present everywhere in the environment and that responses to exposure vary greatly among individuals. (Photo: Heavy mold growth on the underside of spruce floorboards)

There are no accepted standards for molds sampling in indoor environments or for analyzing and interpreting the data in terms of human health. Most studies are then based primarily on baseline environmental data rather than on human dose-response data. Neither OSHA or NIOSH, nor the EPA has set a standard or PEL for molds exposure.

Mold growth on air diffuser in ceiling
Miller et al. (1988) stated that it is reasonable to assume there is a problem if a single species predominates with >50 CFU/m³, that <150 CFU/m³ is acceptable if there is a mix of benign species, and that there is no problem when up to 300 CFU/m³ of Cladosporium or other common fungi is isolated. There is no source material to support these assertions, as few inhalation studies have been conducted.

References

American Academy of Pediatrics Committee on Environmental Health. 1998. Toxic effects of indoor molds. Pediatrics. 101:712-714. 11/23/03

Centers for Disease Control and Prevention. 2002. State of the Science on Molds and Human Health. 11/15/03

US Environmental Protection Agency – Indoor Air Quality – Molds. 11/15/03

Kuhn, D. M., and M. A. Ghannoum. 2003. Indoor mold, toxigenic fungi, and Stachybotrys chartarum: infectious disease perspective. Clin Microbiol Rev. 16(1):144-172. 11/15/03

Miller, J. D., A. M. Laflamme, Y. Sobol, P. Lafontaine and R. Greenhalgh. 1988. Fungi and fungal products in some Canadian houses. Int. Biodeterior. 24:103-120.

Morbidity and Mortality Weekly Report – Centers for Disease Control and Prevention. 2000. Update: Pulmonary Hemorrhage/Hemosiderosis Among Infants --- Cleveland, Ohio, 1993-1996. 49(9):180-184. 11/17/03

Nelson, B. D. 2001. Stachybotrys chartarum: The Toxic Indoor Mold – APSnet. 11/23/03

What Types Of Mold Are Considered Toxic Mold

"Toxic mold" is a term that is used to describe types of mold that are considered deadly to humans. Most people believe that the name refers to one particular species of mold; however, it encompasses hundreds of species, a small fraction of which are not very harmful to the human body. Black mold is commonly used as a name for the most harmful mold species, which happen to be black in appearance. However, even molds of a different color can be toxic to the human body.

Any place that is dark and where there is an accumulation of moisture, is a potential breeding pool for mold. Mold can grown on almost any organic surface as long as moisture and oxygen are present. When large amounts of moisture build-up in buildings, or building materials mold growth will occur. It is virtually impossible to remove all indoor mold and mold spores, but it is possible to manage.

People are exposed to some amount of mold everyday. When mold is growing on a surface, spores can be released into the air where a person can then inhale them. A person who is subject to inhaling a large amount of these spores may be subject to some medical damage.

There are five categories of toxic mold. They are Cladosporium, Penicilium, Fusarium, Aspergillus, and Stachybotrys. Some of the species included in these categories may only cause hay fever-like allergic reactions, while others can cause potentially deadly illnesses. All five of these mold families can be found lurking indoors, in damp spaces. Each has its own particular characteristics that can greatly affect whatever organism or material it contacts. Indoor mold is not always obvious. Mold can manifest on hidden surfaces, such as wallpaper, paneling, the top of ceiling tiles, and underneath carpet.

Stachbotrys

The toxin produced by Stachybotrys chartarum is the most deadly. It has been tied to diseases as minor as hay fever, to those as serious as liver damage, pulmonary edema, and in the most severe cases, brain or nerve damage and even death. It has also been linked to severe illness in infants. Those with compromised immune systems, small children, and the elderly are highly susceptible to illness when they come in contact with this species of mold. Some symptoms associated with exposure to Stachbotrys include:
respiratory issues
nasal and sinus congestion
eye irritation
sore throat
hacking cough
chronic fatigue
central nervous system issues
aches and pains

Cladosporium, Fusarium, and Penicillium

These mold families have been connected to illnesses such as nail fungus, asthma, and also infections of the lungs, liver, and kidneys. Additionally, Fusarium may cause gastrointestinal illnesses, and even illness which affect the female reproductive system. Chronic cases of Cladosporium may produce pulmonary edema and emphysema.

Aspergillus

The least serious of the toxic mold groups, the Aspergillus mold family consists of over 160 species. Only 16 of those cause illness in humans, none of which are fatal if treated.

Toxic molds produce chemicals during their natural growth that are classified as toxins or poisons. The types that have been found to have profound effects on human health, are given the label of "toxic mold."

Toxic molds are all very dangerous if allowed to grow inside the home. Proper precautions should be taken to prevent and eliminate their growth. These measures should include eliminating every material that nourishes the molds, such as old remodeling materials left in a basement. Also, never try to determine the type of mold in your home. Contact a professional to test any mold colony you may find, and consult with your family physician.

Remodeling Your Home? Have You Considered Indoor Air Quality?

Ventilation for Homes

In general, you should address the following issues when remodeling your home.

• Using Ventilation to Contain Dust and Other Pollutants

If too little outdoor air enters a home, pollutants can sometimes accumulate to levels that can pose health and comfort problems. Likewise, one approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming in.

Outdoor air enters and leaves a house by: infiltration, natural ventilation, and mechanical ventilation. In a process known as infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors (air may also move out of the house in this manner — this is called exfiltration). In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Finally, there are a number of mechanical ventilation devices, from exhaust (vented outdoors) fans that intermittently remove air from a single room, such as bathrooms and the kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.

Unless they are built with means of mechanical ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky."

Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air-conditioner with the vent control open increases the ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants, including moisture, directly from the room where the fan is located and also increase the outdoor air ventilation rate.

Ideally, new homes will be built to minimize leakage to control energy loss, improve comfort, and minimize the transport of moisture and pollutants through the building shell. These homes should then also have mechanical ventilation to remove pollutants generated in the home and provide outdoor air in a controlled manner. Whether a mechanical ventilation system makes sense in your existing homes depends on the house, your existing heating, ventilation, and air-conditioning (HVAC) system, and the changes you have planned. You should discuss this with your HVAC contractor. A local Weatherization office, or building performance contractor, might also be able to help you with this decision or point you to local experts.

How much ventilation do I need?

The American Society of Heating, Refrigeration and Air-Conditioning Engineering, or ASHRAE at www.ashrae.org provides procedures for determining whole-house ventilation rates in its Standard 62.2, "Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings". The standard also provides requirements for exhaust ventilation for kitchens, bathrooms, and other point sources, such as clothes dryers and venting for fuel-burning appliances.

Can you imagine resting your arm on your wall talking to a friend at a house party just to watch bedroom wall cave in. This interesting information was posted by ABC news the other day and I thought I re-share. I have had one case of this in Northeast Ohio that was a nightmare and a lesson for the owner. Forget about killer bees and voracious fire ants. Aggressive termites that can destroy a new house almost before the paint dries and may be heading for a home near you.

Formosan termites cause about $300 million in damage in New Orleans each year, and now they are moving north, east and west. They've already been found in at least 11 states, and scientists say they can attack with such vengeance that they make domestic termites seem almost tame.

East Asian Immigrants

These fierce little critters arrived in southern ports from East Asia at the end of World War II and lay low for decades, gradually increasing their numbers until they were strong enough to attack with gusto. For years now they have plagued New Orleans, which seems to have been built for their specific needs, and scientists have all but given up hope of ever eliminating them from that area.

They've already eaten through scores of structures in the city's famed French Quarter, and when they are finally flushed from a building they take up residence in living trees. Thousands of trees have been killed by the termites, many of which have fallen on structures, causing even more damage.

Ed Bordes, director of the New Orleans Mosquito and Termite Control Board, estimates that 30 percent of the city's live oaks and cypress trees are now infested.

Until fairly recently, scientists had thought the termites were pretty well isolated in the Deep South, but that clearly has changed. Damage estimates across several states now range between $1 billion and $2 billion per year, about the same as caused by all the domestic species combined.

Power in Numbers

Formosan termites have established strongholds from Florida to California, and although scientists first thought the termites would restrict their habitat to warm areas, that may not be the case. Those damp basements in northern regions may be very much to their liking.

According to the Agricultural Research Service of the U.S. Department of Agriculture, which is heading up a New Orleans-based Formosan termite project called Operation Full Stop, these hungry little devils are the most voracious termites in the world. Here are a few reasons why:

Their colonies are huge, thus enabling them to do great damage in a very short period of time while fighting off nearly all efforts to bring them under control. A colony of domestic termites usually ranges in the thousands; Formosan colonies number in the millions.

Domestic colonies will eat about 7 pounds of wood per year. A Formosan colony will eat about 1,000 pounds per year.

They don't just eat wood. When they get thirsty, Bordes says, they can eat the seals out of high-pressure water lines to get at the moisture inside. And they can penetrate cement, brick, plastic and other materials to get to food and water.

A queen termite can lay 2,000 to 3,000 eggs a day, ensuring the survival of colonies that can last for decades.

Come springtime, New Orleans residents can look forward to something locals describe as nothing short of terrifying. Colonies will send out winged "soldiers" by the millions, forming flying armadas that can almost turn the sky dark as they seek out new areas for harvesting.

They're not particularly discriminating. They like new houses as well as old. And it doesn't take them long to do a lot of damage.

Eradication Impossible

By the time they were discovered in one 2-year-old house, they had already eaten out one wall from the basement to the roof, according to scientists who are working desperately to come up with a means of controlling the termites. That doesn't mean eliminating them, at least not for New Orleans.

"Eradication is not a likely scenario," according to one report from the Agricultural Research Service.

But at least the scientists know where to start. New Orleans has become a working laboratory, with residents setting out traps to capture enough of the little beasts for scientists to study. Formosan termites are there in great numbers because they couldn't have designed it better themselves, at least from a termite's perspective.

The city has just the right climate, humid and hot. And many of those wonderful old buildings that dot the city's historical areas are sitting directly on the ground, giving the subterranean termites easy access. Many of the buildings share common walls, allowing the termites to move right on down the street without even venturing outside.

They also build underground tunnels extending hundreds of feet in various directions, thus expanding their options.

According to researchers, sometimes nobody knows there's a problem until a wall falls down.

Fighting Back

The best defense appears to be an offense, according to the scientists. Once the termites establish themselves with huge colonies, it's probably too late to do much about it. So the goal is to nip it early, identifying the termites as they move outward and wiping out colonies before they get too large.

Unfortunately, the critters are pretty clever. Other termites are routinely treated by injecting poison into the ground, but Formosan termites can just move their nests above ground, thus avoiding the toxins.

And not a lot of toxins are effective. The most potent treatment, chlordane, was outlawed in 1988 because it remains active in the soil for 25 years, thus threatening human health as well as other animals. Scientists are now experimenting with growth regulators that will keep the termites from maturing, and they are looking for biological ways to inhibit procreation and even communication within the colony.

They've made some progress, but for now the Formosan termite still has the upper hand. It will take a persistent, expensive, grass-roots effort across many states to bring the problem under control.

Stanley Stepak Jr. M.A.

The Need for Mechanical Ventilation

History of Ventilation in Houses
Houses need to have an indoor/outdoor exchange of air to replenish oxygen used by the occupants and to remove pollutants generated by breathing, household activities and emissions from building materials and furnishings. For many years, houses were constructed without mechanical ventilation systems and relied on air leakage through the building envelope to provide this indoor/ outdoor air exchange during the winter months.

In the past, this natural form of ventilation worked fairly well. Houses built before the 1960s tended to be quite leaky and pressure differences between the inside and outside, caused by wind or temperature difference, were sufficient to provide a significant amount of air exchange most of the time. However, a leaky building envelope does not always guarantee adequate air exchange. The movement of air requires both a pathway (e.g., a leak) and a pressure difference, and even a leaky house will experience periods when there is no indoor/outdoor air exchange. These periods are most likely to occur during the spring or fall, when winds are light and there is little or no indoor/outdoor temperature difference that can create a stack effect. The leakier the house, however, the less frequent the periods of inadequate air exchange.

Since most fuel-fired systems consume air from the house, and this air must then be replaced by leakage from outdoors, the operation of fuel-fired systems promotes some indoor/outdoor air exchange. The chimneys associated with these systems also provide a major leakage point, thus promoting air exchange even when the heating system is not operating. As well, a chimney tends to raise the level of the neutral pressure plane, thus reducing the outward pressure difference across the building envelope and, with it, the potential for interstitial condensation (i.e., condensation that occurs within the building envelope) caused by air leaking out of the house.

In houses built prior to the 1960s, the amount of air exchange provided by leakage was generally regarded as sufficient. But in the '60s, a number of factors changed this picture, including the increased use of electric heating in houses. Unlike fuel-fired systems, electric heating systems do not require the replacement of air, nor do they require chimneys. Consequently, electrically heated houses have a greater tendency to experience high humidity levels, interior surface moulds and interstitial condensation.

In the early 1970s, in response to these problems associated with electrically heated houses, Canada Mortgage and Housing Corporation (CMHC) took the step of requiring all NHA-financed electrically heated houses to incorporate exhaust fans, a requirement that was eventually incorporated into the National Building Code. By the mid-70s, these problems had became so apparent that CMHC contemplated not allowing electric heating in houses financed under its National Housing Act mortgage insurance program.

In addition to the increase in the use of electric heating, the 1960s brought the construction of houses that were much more airtight as a result of new products and practices, which included the substitution of panel sheathings, such as plywood and waferboard, for board sheathing; the replacement of paper-backed insulation batts by friction-fit batts and polyethylene film; improved caulking materials; tighter windows and doors; and more efficient heating systems.

When the energy crisis developed in the early 1970s, considerable emphasis was placed on reducing air leakage in order to conserve energy. The use of electric heating systems was encouraged and higher efficiency furnaces were developed further reducing airchange rates in buildings. This trend towards greater airtightness and higher efficiency furnaces gave rise to concerns that the exchange of air in houses by natural means might be insufficient in some instances to provide adequate air quality thus increasing the risk of health problems among the occupants. Condensation problems resulting from higher humidity levels were also a concern.

How Much Indoor/Outdoor Air Exchange Is Necessary?
The air-change needs of houses are not uniform. Not only do they vary from house to house according to the number of occupants, and the presence and strength of various pollutant sources, but, for any given house, they also vary with time as occupants come and go, and pollutant sources wax and wane. Nevertheless, ASHRAE Standard 62, Canadian Standards Association Standard CAN/CSA-F326 and the National Building Code of Canada (NBC) have all established levels of air change that can be expected to meet the peak or near-peak needs of a majority of normal households. (The latter two are based to some extent on ASHRAE Standard 62.)

All three approaches suggest an air change rate of about 0.3 air changes per hour (ach). This is the level of air change used internationally as the norm in terms of analyzing the success of various ventilation schemes. Again, it is recognized that few, if any, houses require constant air change at the rate of 0.3 ach. However, if a house is so tight that leakage fails to provide this level of air change for significant periods of time, it is likely that many such periods of shortfall will coincide with periods when this level of air change is required. When this happens, poor indoor air quality, high humidity, surface moulds and interstitial condensation can result.

How Airtight Are Recently Built Houses?
In 1989, a study to determine the airtightness of recently constructed houses in various regions of Canada was conducted. Airtightness was measured by carrying out fan-depressurization tests on nearly 200 houses throughout the country. The test results were analyzed to estimate the indoor/outdoor air change rate that could be attributed solely to the air leakage likely to be experienced by each house over a typical heating season. The results of the study allowed the researchers to make the following predictions:

• More than 70% of the surveyed houses would have an average air-leakage rate of less than 0.3 ach over the entire heating season.
• Almost 90% of the surveyed houses would have at least one month during the heating season when the average air-leakage rate was less than 0.3 ach.
• Virtually all of the surveyed houses (99%) would have at least one 24-hour period over the heating season in which the average air-leakage rate was less than 0.3 ach.

These results seem to indicate that a majority of houses being built in Canada using normal construction practices are close enough to being airtight that air leakage through the envelope cannot be relied on to provide the rate of air change deemed necessary to maintain adequate indoor air quality in a typical household. While the rate of air change through the building envelope may be adequate most of the time, it may not be all of the time. Therefore, to ensure that a satisfactory rate of air change is attainable at all times throughout the heating season, these houses must be provided with mechanical ventilation systems.

Characteristics of an Ideal Mechanical Ventilation System

Currently available technology is not able to provide an ideal mechanical ventilation system for houses. But before looking at the methods of mechanically ventilating houses that are available today, it is helpful to identify the characteristics of an ideal system:

Operate when needed
The system would operate whenever additional indoor/outdoor air exchange is needed and would do so without the need for occupant intervention.

Operate only when needed
This is important since a mechanical ventilation system has costs associated with it — the cost of the electricity to run it and the cost of heating the outdoor air that the system brings in. (The latter can be reduced by incorporating heat-recovery capabilities in the system, but cannot be eliminated altogether.) Therefore, the system should not operate during those periods when no indoor/ outdoor air exchange is required. The length, timing and frequency of such periods vary from household to household. Air exchange is not required when:

• there are no occupants in the house
• there are no activities or processes underway that generate pollutants
• there is sufficient air exchange due to wind or stack effect to meet the household's needs.

Provide needed amount of air exchange
The system would be able to deliver enough outdoor air to meet the probable maximum needs of the household. It would also be capable of modulating delivery so that it did not deliver more outdoor air than required at times of reduced need. A system that does not have this capability is likely to provide too much outdoor air most of the time it is in operation, resulting in excess energy costs and low humidity. As well, a system that is unresponsive can annoy the occupants, possibly to the point that they simply turn it off altogether.

Distribute outdoor air where needed
It is not enough that the mechanical ventilation system change the air in the house as a whole to meet the standard of 0.3 ach. The system must also be able to deliver the outdoor air to those parts of the house where the occupants are likely to spend most of their time — the living room, the kitchen and the bedrooms.

Be quiet
The system would be quiet enough so that the occupants would not be tempted to turn it off to reduce noise.

Not interfere with other systems
There is significant potential for mechanical ventilation systems to interfere with the operation of other systems, such as certain types of fuel-fired heating systems. Under these circumstances, if the ventilation system creates a high negative pressure in the house, the products of combustion (which can be harmful to the occupants) can spill into the house rather than flowing up the chimney to the outdoors.

Not interfere with the building envelope
The system would not create significant positive pressure in the house since this could drive humid air from the house through the building envelope, resulting in interstitial condensation.

Demand-Controlled Ventilation

The first two characteristics of the ideal mechanical ventilation system described above are related to the issue of control. A system that embodies these characteristics is known as a "demand-controlled ventilation system." Such a system would ideally be controlled by an array of sensors — one for humidity and one for every possible pollutant that the ventilation system would have to respond to, including carbon monoxide, carbon dioxide, formaldehyde, volatile organic compounds, etc. The system would bring in outdoor air and/or extract indoor air until all of these sensors determined that specific pollutants were at, or below, predetermined safe levels. Whenever a sensor detected a pollutant above its safe level, the ventilation system would operate.

A less-than-ideal demand-controlled ventilation system would have at least one sensor. For example, many ventilation systems are controlled by dehumidistats: the system operates until the dehumidistat has determined that the humidity in the house is at a safe level. Excess humidity is one of the main reasons that ventilation is required, but not the only one. The amount of ventilation required to control humidity may not be sufficient to control other pollutants since this depends on the activities of the occupants, on the relative strengths of other pollutants and on the level of humidity.

Carbon dioxide (CO₂) sensors are sometimes used to control ventilation systems in large buildings, and this technology is just now becoming available for residential use. Increasing CO₂ concentration is usually a good indicator of decreasing air quality but it may not be adequate in cases where there are unusual pollutants, such as those generated by certain hobbies.

The ideal system requires the full array of sensors mentioned above. However, at present this ideal is not attainable because:

- there is insufficient knowledge and information to determine

- which pollutants should be monitored, and

- what the acceptable levels for a particular pollutant

- practical, reliable and economical detectors for all pollutants of concern are not available.

While research and development is underway in many countries to try to address these issues, breakthroughs are not expected in the near future.

For a discussion of current approaches to mechanical ventilation systems for houses, please see Construction Technology Update No. 15.

References

1. ASHRAE 62-1989, Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA.

2. Standard CAN/CSA-F326-M91, Residential Mechanical Ventilation Systems. Canadian Standards Association, Etobicoke, ON.

3. National Building Code of Canada, 1995. Canadian Commission on Building and Fire Codes, National Research Council of Canada, Ottawa.

4. 1989 Survey of Airtightness of New, Merchant Builder Houses. Haysom, J.C., Reardon, J.T., and R. Monsour. Indoor Air '90: The Fifth International Conference on Indoor Air Quality and Climate, v. 4, Toronto, 1990.

5. Residential Air System Design. Heating Refrigerating and Air-Conditioning Institute of Canada (HRAI), Islington, ON, 1986.

6. Complying with Residential Ventilation Requirements in the 1995 National Building Code. Canada Mortgage and Housing Corporation, Ottawa, 1996.

7. Airtightness and Energy Efficiency of New Conventional and R-2000 Housing in Canada, 1997. Canada Centre for Mineral and Energy Technology, Natural Resources Canada, Ottawa

Consumer question:

Hi: I have the 8570 thermostat pn 61000229 rev c with a 700a humidifier; ADHC model 58; 61000501 rev b.
The adhc is wired to the 8570 for activation. The supplied outside sensor is also used. It works but intermittenly the 8570 screen goes blank while operating and causes the adhc "call dealer for service" light. the E4 code appears on the adhc. I had the heating tech out for annual service and could not find anything wrong. The only other symtom that I noticed was it occurs in the temp range freezing or above. During continous freezing weather, it did not seem to need to be reset as much.
I have rechecked the wiring between the 8570 and adhc and it is correct. The intermitten screen blank on the 8570 makes me believe that either the unit is faulty or an intermitten power loss.  Any thoughts?

Aprilaires' response:

Consumer question:

Why does the water run out of the bottom of the humidfier. Just installed a new water panel.Could it be that too much water is going into the unit?
 

Aprilaires' response:

Consumer question:

I plan on replacing my (2) 760 Humidifiers with two new 700 humidifiers and would like to receive installation instructions, particularly the wiring. Can you assist - I could not find anything on the site.

Aprilaires' response:

Consumer question:

I have a Aprilaire 600m model and should I conect the water supply to the hot or cold line.

Aprilaires' response:

Consumer question:

I plan to install the UV-C light in the supply air plennum above the AC evaporator coil. How far away from the humidifier should the light be? I understand the UV light may damage plastic parts? or is there no problem?

Aprilaires' response:

Consumer question:

Can I set my air cleaner to a mode in which it will only be active when the furnace (or air condition) is running? And what is the difference between the Constant Cleaning mode and the Allergies mode - is it that the Allergies mode shuts the air cleaner after 24 hours and then what?

Aprilaires' response:

Consumer question:

I didn't notice this until recently, but our Aprilaire 760 runs regardless of the furnace blower running, whereas our 550 model does not. Is that typical for the 760?

Aprilaires' response:

Consumer question:

Does anyone make in-the-wall humidifiers that are silent ( like ultrasonic ) but won't put out minerals or chlorine? We want something for our bird room, that won't make noise when it comes on, like our Aprilaire 360 does, because we don't want to scare the birds at night while they sleep.

Aprilaire response: