Air Purification Systems

A home built with any effort toward energy smart building techniques will likely be a home that is tight enough to need a ventilation system. We've talked about Energy Recovery Ventilators (ERV's),  a green building technology, a lot in other posts because they are an important part of a tight, energy efficient home. Typically an ERV will have its own small duct system. 

Besides a ventilation system, another component of excellent indoor air quality is the main duct system itself. Duct systems that are well-built and have excellent air filtration and other add-ons can greatly increase air quality in the home. 

Starting from the bottom up, what makes a good duct system? For starters, the duct system should be computer-modeled with proper air flow to, and from, each room  Next, the system should be designed with sheet metal ducted cold air returns. Too many builders use the framing spaces and drywall as cold air returns, which makes for poor air flow and poor air quality in a home. 

Air is a fluid, so getting a laminar, orderly flow of air means that the ducts should have soft sweeps rather than hard 90-degree angles. All ductwork should be sealed with mastic and of course you'd never put a duct outside the conditioned space of the home, even if it has an insulation wrap.

Once you have a well-made duct system that moves air efficiently, you next should look at the air filtration system. Upgrading here is a low-cost way to greatly increase air quality in a home. A MERV rating - Minimum Efficiency Reporting Value - measures the effectiveness of air filtration on a scale of 1 to 16. Typically, you should have at least a MERV-10 filter in your home, but these days, you can even get MERV-13 filters that still allow for good air flow. 

High-efficiency particulate absorbing (HEPA) filters with a MERV rating of 16 are also effective air cleaners, but they are usually installed in a separate branch of the duct system. They can impede air flow too much to be added to a normal return air duct system.

In addition to filtering air, you could install a biocide chamber, which uses ultraviolet (UV) light to actively kill bacteria, viruses, and mold spores in the air. These particles still need to be filtered out of the air, but at least they won’t reproduce. 

The last variable regarding indoor air quality is the humidity, or moisture content, of the air. A building with about 30 to 40 percent relative humidity in the winter will feel comfortable without drying out skin and nasal passages too much. Ideally, you'd like a home to be more like 45 percent in the winter, but for American windows and construction methods, that means risking condensation and mold however. Humidity feels good to humans however, and a more humid home can be kept at a lower temperature and feel warm. 

In the summertime in Michigan, we have the opposite problem - we are trying to get rid of humidity to keep our home below 60 percent. A tight, well-made home doesn't need much air conditioning to stay cool though, so sometimes we have to dehumidify in the summertime to keep comfort optimal. A house that is 80 degrees and dry feels comfortable, but a house that is 68 degrees and humid just feels cold and clammy. Getting our humidity right for the season makes a big difference in the comfort of a home.