I have a question regarding the use of filters in forced air heat systems.
I have a new home with forced air heat. There is a filter at the furnace in the return air plenum and also a filter at each of four air returns in the house.
I need to replace the filters which are the cheap .75 jobs. I’m going to get a better grade filter.
My question is this. Should I be “double” filtering, that is to say, replace all of the filters, or should I simply filter at the furnace only and omit the filters at the various returns. My concern is that there may be a possibility of reduced air flow if I replace all filters with the improved grade.
Thanks for your help.
Replies
In general, you only "need" the one filter, and doubling up can cause enough reduction in air flow to (slightly) affect furnace efficiency and/or cause icing with the AC. However, if the main filter is, say, 20x20 or 400 sq in, and the total sq in of the other filters is, say, 1200, then the airflow reduction due to those extra filters will be significantly less than if you simply had two 400 sq in filters back to back.
The other thing you can do is use a high E main filter and leave crummy fiberglass filters in the other locations. They then won't block airflow enough to notice, but they'll still help keep dirt out of the ducts and lengthen the life of the (expensive) main filter.
Mako, see my answer to you at 39736.2 Paul
Thanks much, that's what I've done.