Hi. This website is great; there is really good information. My question is regarding large filters. My furnace requires a 5-inch pleated filter, but because these are hard to find I have placed 5 1-inch pleated filters from 3M. Is this going to restrict too much airflow? Should I buy a 5-inch or cut back to 3 or 4 1-inch filters? Thank you so much.
You should remove 4 of those filters immediately because they will have a negative impact on air flow and operating efficiency will be reduced. Stacking filters in that way will have the same effect on your system as a dirty air filter. Dirty air filters and poor duct design are two of the main causes of poor air flow.
Residential heating and air conditioning systems are not designed to accommodate more than one filter and five pleated filters stacked could cause major problems for you.
Potential problems with low air flow in an air conditioning system
Air conditioning systems are designed to have 400 CFM of air flow to operate at maximum efficiency. 450 CFM is required for heat pumps. There are a number of potential problems that can result from reduced air flow when stacking air filters in an air conditioning system.
- Reduced air flow which can cause poor air distribution throughout you home.
- On an air conditioning system the evaporator coil can ice up.
- Operating efficiency will be reduced which means longer run times and higher operating costs.
Potential problems with low air flow in gas or oil furnaces
- Poor air flow is one of the primary causes of heat exchanger failures. When heat exchangers fail carbon monoxide can escape into your home and cause carbon monoxide poisoning.
- Uneven temperatures or cold areas in your home
- Lower operating efficiency
A 5 inch filter can be left in the system much longer than a 1 inch filter, 6 months or longer depending on a number of factors such as pets, traffic in and out, kids and so on. Each home would be different. Also a 5 inch filter would have less impact on air flow than a 1 inch filter.