Thx much for the ideas.
For CFM and Fan speed:
The Heil model # is H9MVX060F12.
You're right there are 4 fan speeds. I read the install manual and it stated that the 'speed taps are set based on a nominal 400CFM per ton cooling and the basic mid range on the temperature rise for heating.'
I looked further, and found the 'Circulation Air Blower Data' for the model. http://icpindexing.toddsit.com/documents/086477/44071202403.pdf
(see page 3 for the *9MVX060 model Air Blower data)
I checked the DIP switch settings for the fan speed setting on the furnace circuit board, and it's currently set at the factory setting for High Speed (*00) for cooling, which means 1239 CFM for High-Cool and for Low-Cool it's 991 CFM (80% of high cool) if I'm reading right.
Are these the correct data I can use?
So if like I thought before, energizing only the 1st-stage Low-Cool setting always
, the air-flow would be 991 CFM
Would that have any undesirable effect when the 3-ton compressor is operating at full capacity (e.g. coil freeze)?
For cabinet noise:
I had this noise problem with the older furnace also. The old furnace was a Lennox 80% furnace.
The furnace sits vertically in a cabinet at the corner of a hallway corridor. There are two 26" x 12" size vent holes at the bottom of each wall corner that allow return air to be pulled into the bottom of the furnace where a filter is positioned to filter the incoming return air.
I wonder if these two 26"x12" vent holes for the return air are good enough for the 1239 CFM air flow when the fan is on high speed?
(these large vent holes on the two wall corners have lattice-like wood covers so the effective vent size would be smaller)
The noise issue was there with the older furnace as well. It just seems w/ the new furnace the noise is same.
I've talked to two HVAC contractors, and they both suggested to install a duct piping in the crawl space and then get return air from another opening (floor opening). The duct piping will eliminate the noise according to these two HVAC contractors.
*** BTW, two additional questions:
1. For heating:
If I set the thermostat to SS (single stage), it'd always only
energize W1 (Low-Heat) setting regardless of how long it needs to heat the house to get to the desired temperature.
Would that be ok?
As this would mean having the low-heat secondary heat exchanger
for extended time (if I need to heat up the house in the morning the first time, it'd take about 45min to gain the needed 10F) -- would that be overburdening it?
Would that cause any undesirable side-effects? (overheating any other components when running the low-heat exchanger continuously for 45 mins)
2. I keep seeing aluminum foil-like pieces coming out of the air duct vents from time to time. I never saw these w/ my previous old furnace.
The air ducts in the attics are paper-like air ducts so I don't think these aluminum foil pieces are air duct materials.
Would these be from the new furnace?
Thx much for help.