Replies

1. 
   MarkH128 | Oct 27, 2002 03:18am | #1

   One of the guys is probably right. I'd think it would not be a problem to use the filters, but they probably aren't needed either. So I'd leave them out myself, but put them in if you want them and they don't seem to be causing a problem.

1. 
   TooManyTools | Oct 27, 2002 07:37am | #2

   It's mainly a matter of economics.  Having the pre filters in will result in longer life for the high eff. filter but will cost you more in fan energy.  The high efficiency filter will catch everything the pre filters would.  Can't think the added pressure drop would effect your furnace fan's life.  Put a good ammeter on the fan w/ the filters in then out and plug your electric rates and filter costs  in.  You may find you use just as much electricity with them out due to the higher cfm flow you will get with the lower pressure drop.

2. 
   TLRice | Oct 29, 2002 04:09pm | #3

   Robert,

   "My two return air grates are sized for the standard disposable filters that need to be replaced on a regular basis - they fit in the opening behind the grate. The company that installed the heat and air system recommended using the filters at the return air grates for extra filtration."

   The direct answer to your question is that no additional filtration over you high efficiency space guard is recommended. The others are unnecessary

   The company that installed this system, installed only 2 returns? Sounds questionable. How large is the system? How large are the returns?

1. 
   rjw | Oct 29, 2002 04:41pm | #4

   Tim:

   The direct answer to your question is that no additional filtration over you high efficiency space guard is recommended. The others are unnecessary

   Is that because they just won't accomplish anything worthwhile, or that they could reduce air flow through the system?

   I was thinking that using the fiberglass mat type as a "pre-filter" would sort of be like the metal mesh filters used in electronic air filters to screen out the "big chunks."

1. 
   TLRice | Nov 01, 2002 02:18pm | #6

   I made the assumption that this is not a construction site or a place that has an inordinate amount of airborne debris/dust. In this situation, a relatively, normal environment, the "rough" filters will do very little but increase the resistence of the system. High efficiency filters are, as the name applies, highly efficient. So the answer is both.

   "I was thinking that using the fiberglass mat type as a "pre-filter" would sort of be like the metal mesh filters used in electronic air filters to screen out the "big chunks.""

   I do that in my house. Right now a significant renovation is ongoing and lot of dust is created. I use cheap fg filters in front of a better pleated filter and change the rough filters frequently.

2. 
   ROBERTMC | Oct 29, 2002 04:59pm | #5

   The return air vents measure approx 12" x 30" and 16" x 16".  This is for the downstairs which is about 1600 sq feet.  The upstairs has a separate unit and has smaller return air vents in all the rooms. Not sure what size my system is though.  thanks