Heating basics: Forced air systems have become increasingly energy efficient in the last decade. If your system may have cooled better days and nights years ago, you may want to consider having it completely replaced. If your service professional is tying into an existing system, the older system's age will help determine its compatibility with the newer system.

Air cleaners: Broadly, air cleaners work by mechanical filtration, electrical attraction or a combination of the two techniques. Mechanical or "media" filters strain dust from the air as a fan propels the air through the filter membrane. Electrical-attraction cleaners use a principle similar to "static cling" they charge particles in the air or a collection device in the filter (or both) to create a magnetic attraction between particles and filter.

Electronic air cleaners, which can extract 30 times as much dust as ordinary filters, cost a lot more. In fact, a professionally installed air cleaner could cost $500 to $750, including installation. While this is a substantial sum, it's worth every penny if it offers significant breathing relief to one or more people in your household. But if the price is too steep for you, portable units can be purchased for far less. Of course, the smaller units clean just the air in one room - much like a window air conditioner cools only one room. Electronic air cleaners only need to be cleaned once a year or so because they incinerate the trapped dust.

The Association of Home Appliance Manufacturers (AHAM) certifies some portable air cleaners with a Clean Air Delivery Rate (CADR). This measures how many cubic feet per minute (CFM) of air is cleared of a certain size particle. Three particle sizes are rated: smoke (minute), dust (medium) and pollen (large). The higher the CADR rating, the less time the unit needs to remove a given quantity of certain particles from a specified room size. AHAM-certified models are marked with CADR data.

Air filters: The spectrum of air filters and cleaners are differentiated in a number of ways.

Here's a closer look at the main types: HEPA, which stands for high efficiency particulate accumulation, is a highly effective filter originally designed for removing radioactive particles from air. Today HEPA filters are used in military, industrial and scientific applications and in some portable and room-size residential home air filters. Unfortunately, high replacement cost is a real disadvantage to HEPA filters as they generally must be replaced once every year to 18 months, depending upon use, and they typically cost from $75 to $135. And because the filters are so dense, they require a strong blower to move air through, racking up higher energy costs (though typically less than 10 cents a day). The larger the surface area of a HEPA, the better so find out it's square footage before buying one.

"HEPA-type" filters are not HEPA filters, but some of the pleated types are almost as effective. A filter with this label means that it has not met the rigorous standards of a genuine HEPA. Most range from 25 percent to 95 percent effective at microscopic particle removal. Before buying one, be sure you know how good it is at blocking respirable-size particles. With continuous use, HEPA-type filters must be replaced every year at a cost up to $450.

Thermostats: Whatever kind of heating system you have, don't be shy about upgrading to the most modern thermostat available. Look for one that is versatile and easy to operate. You will want a unit that is sophisticated enough to automatically turn your heating or cooling system on and off based on your lifestyle and work schedule.

A humidifier helps ease skin and nasal irritations and can prevent dry-house problems such as shrinking wood joints. But if not kept clean, humidifiers can spew bacteria, mold, and mineral dust into the air. One of the safest types is the wicking-filter evaporative unit with disposable floating filters kept wet and a fan that distributes the vapor evaporating off them. You must periodically replace the filters and clean the tank with an antibacterial solution.

-- Tips courtesy of HomeAdvisor.com