COPYRIGHT 2017 JAMES DULLEY ( www.dulley.com/sea/ ) - June 2017 - (graphics ref. No. 201u at www.dulley.com/sea/column/2017-jun.htm )

"Select best heat pump air cleaner for your family - meaning of MERV"

Dear Jim: We are replacing our old heat pump and must select the air cleaner or filter for it. Our kids have allergies. What does MERV rating mean and what are the various types available? - Kathy H.

Dear Kathy: Selecting the proper type and quality of central air cleaner or filter may help your children's allergies. Any improvement depends on the specific allergies they have so have your children tested. The sizes of specific allergens vary significantly impacting the selection of the best air cleaner for your family.

Installing the highest-filtration air cleaner is not best for most homes. One can increase the resistance to air flow through the ducts to the point where the heat pump efficiency drops. With lower air flow rates, fewer allergens will even make it to the air cleaner element to be removed.

MERV is short for minimum efficiency reporting value of a filter. MERV is determined by testing how many various-sized particles the filter blocks and it ranges from 1 to 16. A typical cheap one-inch thick fiberglass filter is about MERV 2 at best. A filter used in hospitals for surgery may be MERV 16. My geothermal heat pump uses a MERV 11 filter.

Many common allergens (pollen, pet dander, dust mites) can be removed by a MERV 4 filter. Mold spores vary in size, but a MERV 7 filter can remove most of them. Removing tobacco and other smoke requires a minimum of MERV 13.

High-MERV replacement filters costs more and they must be replaced more often. If your children's allergy tests indicate a high-MERV filter is needed, have your heating contractor install a large (area of filter) air cleaner. Again this will be more expensive, but each filter should last longer without causing air flow resistance. The MERV 11 filter in my geothermal heat pump is 30x32x2 inches.

Most of the filters above MERV 7 use some type of pleated media. This is folded back and forth like an accordion in a stiff paper frame often with some reinforcing wire mesh. Two-inch thick is most common. Thicker ones, up to six inches, do not necessarily filter better, but they can hold more particles before needing to be replaced. This may save some money in the long-term.

Keep in mind, a central filter only removes allergens which reach it. Many of the typical larger allergen particles never get drawn into the return air ducts. They puff up when someone sits on a sofa and settle back down again. This is why also running small room air cleaners is important when trying to control allergies.

For families without allergies, installing one-inch thick pleated media filter is adequate. Its main purpose is to keep dust and dirt from getting into the heat exchanger coils inside the heat pump. Dirty coils can inhibit heat transfer and reduce the system efficiency.

Washable electrostatic air cleaners can be effective. The air flowing over the filter media creates a natural static charge causing particles to stick to it. Rinsing it in the bathtub neutralizes the charge and the particle wash away. They are somewhat more expensive initially, but can last and be effective for years.

The Cadillac of air cleaners uses a combination of thick pleated media and electrostatic grids. This offers the advantages of each. Most furnace manufacturers offer these combination systems which are programmed to work with their computerized thermostats.

Other companies, such as Aprilaire, offer these top-end systems which are compatible with most heat pumps. Its controls allow you to program the timing of the filter (blower) operation to fit your family’s at-home schedule. They also offer apps to control the system from a cell phone.

Dear Jim: We usually run our air conditioner continuously during the summer. Should we open or close our window shades at night? - Donna K.

Dear Donna: This depends on the weather conditions. On a clear night when the outdoor temperature is no more than 10 degrees above the thermostat setting, leave your window shades open. Heat can radiate outdoors through your windows to the cold upper atmosphere.

On hot, overcast nights, the clouds block the cooling effect of heat radiation to the cold upper atmosphere. Close the shades to increase the insulation value of the window glass. With the shades open, more heat transfers in through the glass than be lost from the radiant cooling effect.


















Send inquiries to James Dulley, Publication Name, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.