Editor's note: The System Mysteries is a collaborative creative endeavor between The News and Emerson Climate Technologies. These articles are designed to help clear up some diagnosis misconceptions. This article supplies the solution to System Mysteries article that ran in the March 21 issue of The News.

The hypothetical scenario involved Dave, a residential air conditioning contractor in northern Kentucky, who ran a service call to a 20-year-old, 2,000-square-foot home. He discovered that a 500-square-foot addition had been completed about five years ago to make room for a new bedroom and family room.

The home's 2.5-ton heat pump system provides the primary heating and cooling; a 60,000-Btu, 80-percent AFUE natural gas furnace is the auxiliary heat source. Sheet metal ductwork runs throughout the original portion of the home; duct board and flex duct were installed in the addition. The ductwork is consistent with that typically found in northern Kentucky. A portion of the original ductwork runs through a crawl space under the house.

The homeowners say the addition is usually either too hot or too cold. Their 10-year-old son Jason has been suffering from severe allergies that now border on asthma. They also own a dog.

Dave cleaned mold from the system's A coil on the service call. He noted that the heating-cooling systems were not upgraded during the addition.

The register in the room with the worst hot spot was delivering 200 cfm. It should have been getting 375 cfm. Ductwork is not properly sealed in the crawl space.

If you were in Dave's shoes, what would you tell these customers? How do you help them plan for the future?

Our Solutions

The first step Dave takes is to repair the damaged ductwork in the crawl space below the house. He also needs to repair sagging ductwork in other areas. Afterwards he can remeasure airflow to see if this improves the system's overall ability to cool the room at its current square footage. It may not bring it completely up to where it needs to be, but additional steps may help rectify the situation until these homeowners are ready to purchase a new heat pump.

Dave recommends the installation of a zoning system to control system operation in areas of the house that are not being used. He would like to zone the addition away from the rest of the house so that Jason's room, where he spends a good deal of time at the computer, can benefit from constant air circulation and filtration through a whole-house electronic air filter, another recommendation.

He explains that electronic air cleaners can filter up to 98 percent of large and small airborne particles, including bacteria, pollen, dust, animal dander, viruses, cooking smoke, and tobacco smoke.

Dave also hands the homeowners a copy of an article from a recently published consumer magazine that re-emphasizes previous poor test results of certain room air cleaners. He is keeping several authorized copies on hand to give to customers. In fact, these customers already know about the report; they don't need the article. They indicate that they know about the problems with these cleaners firsthand.

Dave gives Jason's parents information on his company's regular system maintenance, which includes coil cleaning and inspection. This, notes Dave, will help cut down on bacterial growth dramatically. It should also improve the system's capacity and may even reduce the customer's electricity bills and help the compressor run more efficiently.

To help keep the coils clean in between regular maintenance, Dave recommends that the homeowners let him install a ultraviolet (UV) light above their indoor coil. UV lights emit a germicidal UV frequency that penetrates the cell walls of microbes, neutralizing their ill effects. Dave's annual maintenance includes checking to make sure the UV light is working as it should.

Dave's final recommendation to the family is to use a sensor to keep track of relative humidity levels once the heating system is operating again. If relative humidity falls below 45 percent in their son Jason's room, Dave said for them to call him and he will install a humidifier to the main duct plenum. Air that is too dry can also be detrimental to allergy, asthma, and respiratory conditions.

Sidebar: And The Winner Is ...

Congratulations to Dave Hutchins of Bay Area A/C, Crystal River, Fla.! Dave's won this test to find the best solutions for the customer. He will receive a gift card to Bass ProShop. Here is his winning response:

1. Seal obvious duct leaks and recommend a duct blaster, blower door, or Aeroseal test to be on the safe side.

2. Install an electronic air cleaner or MERV 10 or greater filter. This may require duct changes due to increase in external static pressure (ESP). A simple test of the ESP of the duct system will tell, when compared to the manufacturers fan data information.

3. Add an ultraviolet light over the coil to reduce mold. For maximum protection of possible allergens, consider a bypass HEPA filter as well.

4. Replace equipment with the correct size, consider using variable-speed indoor fan with a dehumidistat-type control running at 350 cfm per ton, such as Carrier's Infinity or others. Consider the two-stage compressor as well. This is to maintain lower humidity, reducing or preventing mold and dust mites to relieve allergies. If the budget doesn't allow, design for 350 cfm per ton in cooling, with a PSC motor, to have better than standard humidity reduction in cooling.

5. Redesign duct system for added tonnage and to increase airflow to the required amount for the addition, as well as making any changes needed for the larger system. This could be as simple as adding a parallel trunk from the plenum to the trunk that was added/extended to the addition. Keep in mind the new 3 ton (if that's what the load is) will be operating at 350 cfm per ton, for 1,050 cfm; the old unit may have been designed properly for 400 cfm per ton, for a total of 1,000 cfm, so there may not be a lot of change needed.

Thanks to everyone who sent in a response!

Publication date: 05/23/2005