Question: I have a Honeywell electronic furnace filter on my furnace. The power panel failed and the unit is very expensive to replace. However, I can install pleated air filters in place of the original electronic cells. The filter size is 20 X 25 X 4 inches thick. As a temporary measure, I have installed 3-1 inch thick MERV 8 air filters in parallel into the filter opening.  How does the MERV rating change when the filters are placed in parallel? Is what I have done a good solution? If not, what would you recommend that I do?

I would remove two of those 1 inch pleated air filters ASAP. Installing filters in this way has a very negative effect on air flow and reduces equipment efficiency greatly. Take a look at your air handler to see if there is a place to install a 1″ filter. Most air handlers come equipped with this filter rack.

Take a look at the pictures on this page “where is my furnace filter” if you are not sure where to look. If you can’t find a place to install a 1″ filter, you can get a 20 X25 X4 MERV 12 filter at NordicPure for a very reasonable price.

An air filter change indicator can potentially save you hundreds of dollars on replacement air filters and can even lead to reduced operating costs for your air conditioner, heat pump or furnace.

How is this possible?

• Change your furnace filter or air conditioner filter too often and it’s like throwing money away.
• Wait too long between filter changes and equipment operating efficiency begins to decline.

How often should an air filter be changed?

Manufacturers often differ in their recommended filter change frequency. Some say every month, some say every other month and others recommend every three months and that’s only for 1 and 2 inch filters. If you use 4, 5 or 6 inch pleated air filters, recommendations vary from 3 months to a year.

Filters are expensive, especially the efficient varieties and the 4, 5 and 6 inch types so you don’t want to be changing them more often than absolutely necessary. It’s very difficult to know when a filter has reached the point where it is better to change it than to leave it in the system.

Manufacturers can’t really tell you because they can’t possibly know the conditions in every home, not to mention every geographic area. There are just too many variables to consider. If you follow a set schedule for your filter changes you are probably not getting the best value from your filters.

Leaving an air filter in your heating or air conditioning system too long costs money

If you don’t replace you air filter often enough it begins to impact air flow and causes equipment operating efficiency to decline. A decrease in operating efficiency translates to higher operating costs. This means higher energy bills and nobody wants that either.

If left in a system long enough, a dirty filter will cause air flow restriction and can cause evaporator coils to ice up, heat exchangers to crack, longer run times and other equipment troubles that may require a service technician.

So what’s the solution?

Installing an air filter change indicator eliminates the guessing from filter change schedules. You won’t be throwing money away by changing filters too often and you won’t be wasting money and dealing with the potential problems associated with leaving an air filter in too long.

More about air filter change indicators.

Question: I have recently moved into a house and the furnace uses an electrostatic air filter filter and I am unfamiliar with it.  We have 2 filters one is in the furnace and 1 is leaning up against the wall…the slot is big enough for both filters, do I put them both in or would that restrict the airflow…is the sole purpose of having 2 to alternate when cleaning the other.  Thank you in advance for helping me with this question….thank you also for the info on cleaning it this website is very helpful.

It is fairly common for people to have two electrostatic filters. While one is drying after being cleaned the other is used and they are alternated this way. You are also correct about using both of these filters in a heating or air conditioning system. Installing both filters at the same time would definitely cause problems with air flow.

Restricting air flow can cause many different problems:

Restricting air flow in an air conditioner

• Evaporator coils icing up
• Poor air circulation in the conditioned space
• Increased operating costs due to longer run times
• A decrease in equipment efficiency

Restricting air flow in a furnace

• Furnaces cycling on high limit switches
• Cracked heat exchangers
• Increased fuel consumption due to longer run times
• A decrease in efficiency

The above are only some of the potential problems that can result from restricting air flow.

Question: Do you think there is  any problem with ultraviolet furnace filters as far  as it depleting the inside of the Duct liner or plastic or rubber that the ultraviolet rays bounce off.

It depends on the type of plastic your condensate pan is made of.  Some of the newer drain pans are UV resistant but you would have to check with the manufacturer to know for sure.  UV also causes rubber to deteriorate.

There are a few of things you can do to avoid this potential problem.

- Install the UV air cleaner in the return duct before the ac unit.  This way the light doesn’t contact the drain pan or any other plastic parts.

- Mount it in the supply duct far enough away so that it doesn’t contact the drain pan or any other plastic parts.

- Place a shade of some sort above the condensate pan to prevent the UV rays from contacting the drain pan.  You have to be not to do anything that can potentially affect air flow.

What I recommend is that you install the uv air cleaner in the supply air duct.  This will treat the air before it enters your living space and destroy most mold spores, bacteria, viruses and other pathogens.

I often read that UV lights should also shine on the evaporator coil to destroy any mold that may grow there.  I have worked on thousands of air conditioners and have seen very few with mold growing on an evaporator coil.  I have seen many dirty evaporator coils but that doesn’t mean there is mold.

I have seen condensate pans, drain lines and p-traps with some nasty looking things growing in them that I handle carefully.  The reason things grow in these places is because a lot of contaminants from the air collects there.  The evaporator coil is wet from condensation most of the time and as air passes through the evaporator coil, contaminants collect on the coil and many of these contaminants are washed away with the moisture on the coil as it drains off.  So the coil actually stays fairly clean for a long time when using efficient furnace filters and a lot of the contaminants collect in the drain pan, drain line and p-trap.  You can treat these components with a mixture of bleach and water, about 10 parts water to 1 part bleach.

If, for some reason you are having problems with mold on the evaporator coil contact your service technician and have him or her clean the coil with one of the many chemicals available.  There are environmentally friendlier cleaners available also.

Regarding the duct liner, I don’t think UV light would have any effect on it.

Update Dec31/08

I submited this question (Do uv lamps damage plastic condensate pans and rubber?) to a popular UV air cleaner manufacturer and this is the reply that I received.

Question: I was recently told that I could put (4) 1” inch filters together and use as a replacement for the expensive 4 inch pleated filter in my Aprilaire Spaceguard furnace filter system.

It is never a good idea to stack filters in this way.  It restricts air flow and can cause the air conditioner to ice up, among other things.

Any savings would be quickly lost due to decreased equipment efficiency and possible service calls.

Problems related to restricting air flow.

• Reduced operating efficiency
• Increased operating costs
• Evaporator coil icing up
• Reduced air flow to the home
• Longer run times
• Filters could be sucked into the fan causing damage
• Liquid refrigerant flooding back to the compressor
• Possible equipment failure

If the cost of the filter is a real concern, you could possibly install a 2 inch pleated filter into the Aprilaire Spaceguard furnace filter system.  As long as the outside dimensions are the same as the Aprilaire filter it should work.

When installing the narrower filter make certain that it is installed against the down stream side (toward the air handler) of the Aprilaire unit.  This way, air flow will help to keep the narrower pleated filter in place.  This will only work if the filter is mounted in a vertical position.  If it is mounted horizontally, this will not work and you will have to figure out a way to hold the filter in place.

Nordic Pure Anti-Allergenic Pleated Air Filters Half the price of most leading brands!