Return Air Plenum
Horizontally operated furnaces and air handlers should have a return air plenum
that looks like this
to best enable the equpiment to operate at its maximum efficiency (SEER).
Residential return air is unique. Each installation is different and can provide the HVAC technician with
plenty of challenges ranging from carpentry and plumbing to insulated sheet metal ductwork.
Conventional rectangular returns are universal, economical and easy to transport...
they can be made to fit most any situation,
but they have a multitude of seams and surfaces that must be sealed in the field.
And in many cases, they can be labor intensive to install.
These sheet metal boxes often buckle and leak from being forced into place during installation,
and over time the seams begin to leak when the sealants age and crack...
These buckles allow attic air into the system which lowers the performance and the life of the equipment
as well as contaminating the living area with unfiltered dirty air.
According to a recent article in AIR CONDITIONING, HEATING & REFRIGERATION NEWS; current studies show that 20% - 60% of the loss in SEER is due to leaks in the return air system.
If the loss in SEER could accurately be translated into dollars per month,
assumimg as little as a $10/ month loss due to leakage...
then it does not take long to add up.
Everything else being equal, leaks in the return air system are
As a general rule the return air plenum is the cheapest part of the residential HVAC system.
The home owner is paying for and thus deserves
a leak free system that does not restrict the equipment SEER,
and that delivers clean air for his loved ones to breathe.
As is obvious, the return air is so important
the homeowner should ask his AC vendor how he is going to supply it
and whether or not it is a leak free construction!
So, ... what is the cost effective solution to the real world problems associated with horizontal return air plenums?
In terms of basic cost, that is from the top of the chase to the furnace or air handler
the conventional RAP (see second photo from top) costs the contractor, about $60.00
add a tab collar for secondary return attachment with flex duct, about $4.00
add to this the skilled labor to install the RAP and collar, about $20.00
Thus the approximate cost to the contractor to install the conventional return plenum is about $84.
The cost of the return air is trivial when compared to the cost of the total installation, yet
it has the greatest impact on the monthly operation and depreciation of the equipment.
What is the penalty cost of a slightly substandard residential A/C installation...
if the unit is losing $15 / month in efficiency
and operating eight months per year then:
over a period of three years it costs the home owner $360 direct out of pocket;
adjusted for income tax 1 - .30 = .70
$360/ .70 = his real cost of the inefficiency = $ 514.
And what about cleaning a dirty coil for $350,
or replacing the dirty heating elements?
Ohh thats too much trouble why not replace the whole $5,000 system in eight years?
As the result of using a poorly configured return air plenum.
This, the ECHOES RAP(tm)
a high performance, high efficiency return air plenum
it provides enough aperture to meet the manufacturers requirements for return air volume
and it is fed using quick and easy flex ducts,
has but a few easy to reach seams which are easily sealed with tape,
and it is externally insulated which helps to prevent the growth of mold inside the air stream.
These features allow the unit to operate at its maximum efficiency.
Thus, all other things being equal, it enables optimal equipment performance.
It also allows the unit to be located in an easily servicable, uncongested area.
This plenum can help you provide your customers with cooler, cleaner air
at a reduced energy cost
and longer equipment life.
This is the spirit and intent; exactly what is ment by the term GREEN.
The ECHOES RAP can be made to fit most makes and models of air handlers and furnaces...
Trane, Carrier, Goodman, Ducane, McQuay, Honeywell, Ruud, Bryant, American Standard, Lennox,
Amana, Rheem, G.E., York, Heil, Payne, Janitrol, Coleman, Whirlpool, Weather King, & Comfortmaker
A popular configuration mates a Honeywell F100F air filter to a fan coil.
Fan coil with Z bars for a quick and easy machine side filter attachment.
As you can see, the assembly of the RAP to the filter is fast and clean. It is easily sealed with tape.
This RAP allows for a quick, clean efficient flow of return air to your cooling coils.
This does not constitute professional advice, but as a rule of thumb ... in general ....
3 Tons needs an 18" flex duct.....254 square inches for inlet air
4 Tons needs 18" with a 12" secondary....... 367 square inches for inlet air
5 Tons needs an 18" with a 14" seconday........ 408 square inches for inlet air
Where can the second or third return be placed on the RAP? **** B - C - D
Are you using a machine side filter?
Do you have enough space in the attic to use this style RAP?
The same is true on the supply side...
the collars often leak over time
as the sealant (mastic) dries and cracks.
This high efficiency supply air take off fitting has a 1" perimeter flange with a gasket.
It also has a damper that allows the air flow to be adjusted and balanced.
The conscientious homeowner would use this $25 - $50 item instead of a $2 - $8 collar.
The installed fitting would be externally insulated in the field.
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