Static Pressure Measurments


Old 10-18-13, 10:42 AM
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Static Pressure Measurments

My local HVAC company just finished their install of a 96% efficient, dual stage 90,000 BTU Lennox Furnace. It is connected to a 4-ton A/C unit. My home is 4100 sq. feet, rambler with finished basement. Static pressure measurements, with the 4 inch filter in place and on A/C were:

.24 supply
.41 return
.65 total static pressure

The sales guy came out to see how everything wrapped up and said we could get better numbers on my return if we added one more 10 inch return in my basement, near the heater. We would add it there since it would be more easy to add the return as the rest of the house is finished. He measured my return trunk that runs the length of the house and said it is clearly too small for my home, thus I'm at .41. Said if we added the one more return we should be able to lower that return and thus improve overall flow--which would be key for the summer months and my A/C use.

Not sure what my bids will come in at to add the return but would you guys try to get that return pressure lower so I could be closer to .5, of does this look close enough?

Again, I run a 4 ton A/C and live in an area (Utah) where summer months can get into the high 90s. Home was built in 2001 and is well insulated--but has many high ceilings.
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Old 10-18-13, 11:58 AM
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Did he take measurements with the filter out? A Merv8 filter vs a Merv11 could make the difference. Just a thought before adding but I've seen high eff. filters added to barely adequate ductwork where it made it worse.
Old 10-18-13, 01:07 PM
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If those numbers include the evap coil and filter, your system is okay. 0.5" (ideal) is hard to attain, considering that a decent filter has a pressure drop of 0.15-0.2"+, as does an evap coil.

If not, major changes are required.

But considering that your contractor actually has the sense to measured static pressure, he probably knows what he's doing.
Old 10-18-13, 04:10 PM
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Yes, that was done with Evap coils and filter in place. Merv 8, 4 inch pleated filter. They designed it with all new return air ducting that allows air to flow on both sides of the fan. Furnace sits on top of the air box. Nice design. I'm sure it is common on all new installs. Far better than what I previously had.

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