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!

Question: I have a Water Furnace and currently use a pleated filter with a MERV 5 rating.  how high can I go before I start restricting the flow too much and damage the system?

A Merv 5 filter is really not very efficient.  If you have a properly sized duct system and you change your air filter regularly I see no reason not to use an air filter with as high as a Merv 12 rating.  as Merv ratings increase so does restriction to air flow, so you always have to be careful.  The reason I mention a properly sized duct system is because if the duct system is undersized it will restrict air flow dramatically and is a common problem in many homes.  A very efficient air filter and an undersized duct system are not a good combination.

There are a couple of signs that may indicate an undersized duct system:

-  The air conditioner coil ices up when the filter becomes dirty.  Most systems will do this if the filter becomes extremely dirty but you should not have this problem if the filter becomes only moderately dirty and you change it regularly.

- Whistling sounds coming from around the air handler access panels can be an indication of an undersized duct system.  This can also indicate poorly fitting access panels.

- If your furnace trips of on the high limit switch, this could indicate an undersized duct system.

There are other things that could cause the problems listed above but they are also signs of restricted air flow.

If you have your equipment serviced regularly ask your contractor if the duct is sized properly.  Opinions vary among contractors regarding filters with high Merv ratings.  Your other option is to try a higher Merv rating and monitor equipment operation closely.

Question: With regard to pleated air conditioner filters do you think I can go with a MERV 6 filter or do you think I will be better served going with a MERV 8 filter?

A MERV 8 filter will perform better than a MERV 6 filter but the difference will be minimal. If you are not too concerned about dust a MERV 6 filter will do a good enough job. If you are looking for a big improvement in dust control you may want to try a MERV 11 or 12 pleated filter.

Pleated filters in the MERV 5 to 8 range will stop particles of 3 to 10 microns such as some mold spores, fibers, dust mites, some bacteria and fiberglass among other things.

MERV 9 to 12 filters stop particles of 1 to 3 microns such as smoke, bacteria, spray, fumes, coal dust and auto emissions and many other things.