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HVAC

Our upstairs HVAC, original to the house,
looks awful but amazingly still works.

Main HVAC was replaced by a Goodman in 2013.
Goodman originally had a poor reputation,
I speculate because they would honor warranty for DIY installations,
but are essentially rebranded Amana; my Lexington Goodman was fine.

static pressure Static pressure, generated by fans or blowers, moves air.
Pitot tubes measure moving air's velocity pressure, which I ignore.

Taps for static pressure, measured by manometer in inches of water,
were installed at A and B,
encompassing pressure drops for both filter and AC coil,
along with airflow direction changes (not shown),
each of which also drop pressure by 0.1 or so.

Installing tap at C will enable measuring total external static pressure.

pressure drop, manometer Our main air mover has a 100.0 AFUE rating from EPA (as of 2013),
based on 0.3 water column pressure from A to C.
excluding filter and AC condenser coil.

1" air filter slot at AC coil bottom is rusted and collapsed,
confounding filter replacement.
4-inch media filter upgrade was anyway intended,
first installing a manometer to evaluate pressure drops
and time filter changes.
Manometer mounting screws are for sheet metal, not duct board,
accomodated by taping aluminum flashing to duct board:
 
Included taps are for sheet metal, not fiberglass duct board;
spade bit cut a 7/8" hole for pressure tap B,
 
then tap in flashing scrap was taped over it.
 

Manometer adjustment has minimal range;
this small amount of fluid determined ability to zero or NOT:
 
My Lexington HVAC filter gage showed air pressure increases,
but not actual water column values.

As with most projects involving aluminum duct tape,
paper backing removal is the hardest part;
I used a utility knife and illuminated magnifier...

0.9" pressure drop measured by manometer:

... to AC coil exit A:
 
from tap B in ductboard, before planned new filter location,
is excessive for this air mover, explaining high electric bill
and operating noise louder than Lexington installation.
Another manometer tap C at air mover exit
would reveal even worse pressure drop...

Plenum below our AC coil filter slot probably lacks deflectors
to guide return air around 180 degree turn, increasing pressure drop.
A 5 ton system wants about 2000 CFM air flow
and 1000 square inches of area with normal 1-inch filters.
Stock 22x23 filter is less than 500 square inches...

Honeywell Media Air Cleaner F100F1625 One reviewer noted gap between cover and included filter lets air by.
1x3/4" foam tape fills that gap:

Cheaper and better Filtrete MPR 1550 filters will leave about 1/4" wider gap..