If you you use MERV 12 (or higher) filter and you have old dirty returns you going to go through those filters pretty quick. (if returns are on the floor that does not help either.
You may look at cleaning your air ducts that will help in you situation.
My "old" 1994 2 ton comfortmaker keeping my 1100 sqft ranch at 70 on 100 day and cycling, with no problem and I'm like 500 miles south of you.
I use standard 1" Merv 8, 16x25 and they last like 3 month easy.
I will have my ducts cleaned, continue with the same type of filter, and not expect 71 Degree cooling on the 90 degree days.
15 years ago when I had a blower motor replaced, the guy doing the work told me there are huge differences in the effectiveness of different machines used to clean them. Any suggestions on what to look for in duct cleaning companies or equiptment?
Again I want to thank you guys. From reading these forums a year ago, I was able to choose a very professional instaler for my a/c and furnace. He did a load calc., Manual J, duct evaluation etc. One of the 5 bids that I recieved was from a larger company who would have just sold me an oversized system to match the size of the 24 year old one I was replacing. Without you guys freely sharing your knowledge I would not have known any better. When the inspector came to check on the work, he saw the name of the firm who did the work, and he told us up front he knew the work would be top notch from inspecting over the years. THANKS AGAIN!
The Infinity controler does also control the humidity. I have it set for 0% humidity for the summer, for comfort. I could try turning up the humidity level to speed up the fan, but I think I would rather have lower humidity if I had to choose. Thanks for the tip. That may well explain why the fan does not kick into high. I think we have now had our last days over 90 degrees for the season. We probally won't have many over 80 or 85 at this point. I just did not want to wait a year before dealing with this. Thanks again.
Try setting the humidity around 45%, when it's hot and the A/C is running a lot (therefore removing humidity) you don't need to reduce fan speed. When the unit doesn't run much low speed fan will kick in.
at 900 CFM the rated filter dP is only 0.087" ( not 0.21" @ 1400 CFM) (1400-CFM was the lowest CFM listed on the linked chart for that filter size; I didn't bother to figure it at 1000 or 900-CFM.)
What formula do you use to rough estimate change of filter drop to change in flow rate?
Formula I use to approximately estimate filter static pressure at Different or Reduced Air Flow Conditions – What do you use? (known value 1400-cfm @ 0.21” of filter pd.)
The New filter static pressure = original or old filter static pressure *X’s say 900-cfm/1400-cfm x power2
900cfm/1400-cfm= .642857142 X power of x2 = .413265306*X’s .21” filter static pres. = 0.867” or 0.87" filter static pressure; your figure too.