Air quality should be a big issue for most homeowners, especially those with sensitivities to dust, pollen or mold.
Air quality is affected greatly by the initial construction quality of the home. After construction, the air can only be somewhat controlled and managed by filters, registers, ducts and HRV’s. Homes equipped with FAU’s have the ability to move air throughout the house, so they can play a role in either improving or further degrading the interior air quality depending on the quality and/or state of repair of the system.
Poor air quality can come from many sources, but the primary culprits are:
- Off-gassing of the interior finishes.
- Intrusion of polluted air from the crawlspace and/or attic.
- Infiltration of polluted air from the outside.
Air from outside the home can be tainted with smoke, molds, pollen and dust. Air from the crawlspace and attic can also contain dust, fiberglass particles, mold, mildew, sewer gasses and radon. Off-gassing from inside the home is usually from VOC’s*, formaldehyde, adhesives, solvents, cleaners, paint vehicles, steam, dust, and possibly mold and mildew from damp areas in the home. A full list of items that produce VOCs, as well as information about the chemicals present in various products and materials, is available online from the National Institutes of Health.
So how does this impure or polluted air get into the home?
Well, from basically everywhere! Some newer homes are fairly well sealed off from the attics, crawlspaces and exteriors, but the majority of older homes (prior to 2008) leak air like an open screen door. Even if a home is totally sealed off from the outside, the off-gassing of interior products can be a significant problem. Leaky areas are usually small, but there are many of them and they can sometimes be in surprising places, like around electrical outlets and light fixtures. Typical air leaks happen at chimney flues, doors and windows without weatherstripping, through light fixtures and outlet/switch boxes, crawlspace and attic hatches, unsealed heat registers, window and door trim, exhaust fans without backflow flappers, dryer ducts and cooktop hoods just to name a few. Broken and leaking air distribution ducts can be a huge problem too. Broken air ducts mean that not only is costly, heated air escaping to the voids, but nasty, polluted crawlspace or attic air along with insects, rodents and even reptiles now have open access into the home. The best way to find out if your home is leaking air is to perform a blower door test by a certified technician. This can tell you both how much air is leaking and provide ideas about where the leaks are located.
Filters for your heating system can come in the form of disposable paper type filters, washable filter media and electrostatic filters (also washable). What most people don’t know is that typical, disposable furnace filters are not really much good at improving your indoor air quality. Most homes leak air like crazy so air is coming into the home from all directions all the time. Your furnace system certainly moves this air around and paper filters actually do remove some dust particles from the air that is passed through them but to actually remove pollutants requires much more sophisticated gear than most FAU systems are built to handle. The actual primary job of the furnace filter is to remove and prevent as much dust as possible from entering the furnace and duct system. This is important in order to prevent the dust from accumulating on the interior of the ducting and becoming difficult to remove.
In order to actually improve the interior air quality of the average home requires a multi-step process that goes way beyond simply changing filters. Every home is different, and each will require its own scope of work. We recommend consulting with a certified Healthy Building Science expert.
- Hire a testing company to do a blower door test on your home to learn how much air is leaking in and out and where leaks are located.
- If your home is equipped with a manual damper system. Adjustment of these dampers from heating to cooling season will more evenly balance the heating and cooling temps throughout the different areas of the home. Note: air register in the rooms can be used to direct air but are not dampers.
- Have a trial run early in the fall to test the furnace. If repairs are needed, it is much better to discover that before the heating season.
- Clean the interior of the filter bay and the washable filters at least every six months. More often in dusty environments.
- When replacing disposable filters, care must be taken to select the proper filter and correct size for your furnace. The filter will have arrows on the edges indicating the air flow. Be sure to install them in the right direction.
- Be careful with HEPA filters as they will indeed remove a lot more and smaller particulates than normal filters, but they also clog up faster and thus require changing more often.
- proper filter size is important, as is the installation so that the body of the filter fits snug in the airstream with no gaps. This will ensure that the air passes through the filter and not detour around it.