The heating and cooling in my house is functioning well. One room upstairs
is a little cool when the heat is on, a little warm when the AC is on, but
that's about it. It's a forced air system that was installed to replace a
gravity feed coal furnace.
The system has two air returns. One in the living room, about 12 inches
square, and a giant one in the kitchen, 24 X 30, or 720 square inches. The
duct in the kitchen is formed from two 10 inch deep joists. As I see it,
the joists form a return duct about 28 X 10, or 280 square inches.
With all else remaining the same, can I reduce the opening in the floor to
about 10 x 30, or 300 square inches without harming the intake volume of
To me, it looks like breathing through a straw. You can put a funnel on
the straw, but it won't make you get any more air through the straw. So
does the opening in the floor need to be so huge?
I suspect it's so large only because the duct was that way when the furnace
I can't *see* it from here, and your missing 90% of the required information
to even be able to make an educated guess. Call your *LOCAL*, competent,
licensed, insured, professionally trained, HVAC technician.
The OP missed one important thing. That "funnel" is covered by a web of
sometimes open, sometimes mostly-closed webbing called a "filter". It
restricts the airflow, such that the filter area must be larger than the
duct, unless you use deep-pleated filters (which it ain't likely your
system is equipped with).
The competent local HVAC guy can tell you what the filter area needs to
be for a specific air flow and filter type.
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kjpro @ usenet.com wrote:
No Returns in basements, unless gas (oil) furnaces, water heaters & gas
dryers are tightly sealed off separate from the Return area.
Why wasn't a big Return Run put upstairs for cooling?
Do you live in a hot climate? - udarrell
WISDOM PRINCIPLED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES & WISDOM Principled PEOPLE EMPOWERMENT
the question might be simple.
The house was built about 1903 with a coal furnace. In the last hundred years
had an upstairs, two additions and a bathroom added, and at some point (perhaps
the additions) the furnace was changed to forced air. The present unit is only
10 years old.
The filter is 20 by 30 inches and is inserted in a slot at the furnace, just
the air enters the fan chamber.
The room that is now the kitchen may not have been the kitchen a 100 years ago,
may not have been built with the return in the kitchen. I have no way of
the builders did not include a cold air return upstairs, but it may have been
motivated by the desire to avoid disturbing the lathe and plaster walls.
I also do not know why a "*LOCAL*, competent, licensed, insured, professionally
trained, HVAC technician" did not move the air return to ensure the system was
code. I was not here when the furnace was installed. I know that it was
a "*LOCAL*, competent, licensed, insured, professionally trained, HVAC
because the company's faded sticker is on the side of the furnace.
I'm in northern KY. Midwest climate with mild winters and hot summers.
The unit's ability to keep the house comfortable is not in question. I did
that only one room runs slightly warm in summer and slightly cool in winter, but
was technically not relevant to my question.
I think I failed to ask my question correctly. If I were to ask if the opening
duct could be made larger, I suspect the answer would be "Sure, make it as large
you want it. Just don't change the length or size of the duct itself." So if I
it the other way, "If all things remain exactly the same, can the opening to the
I thought the answer would be easy, like, "Sure. Just don't make the total
area of the opening smaller than the surface area of the pipe." Or perhaps
would be a rule of thumb like, "The surface are of the opening to the duct must
same as the surface area of the duct multiplied by 1.25" or something like that.
I have read a huge amount of HVAC information over the past week, and can't seem
find the answer. So what am I missing?
I'm not trying to re-size the duct or make it longer or shorter. I am aware of
friction coefficients and angles and turbulence and the limiting effect of air
I also know that surface area isn't really appropriate for talking about pipes,
I'm working with the size of the opening. If the size of the opening is larger
the size of the duct, then that looks like a funnel to me.
Am I so far out in left field that I don't even know I'm playing hockey, or am I
least in the ball park?
Udarrell, thank you for your response. If someone asked me how polymorphism can
used in his or her C++ program, and I responded, "call a college educated
with a PHD to write the code for you," I should think that I would be considered
isn't very strong. You'll need to work on that. Find the right
book about reading. I was describing the condition of the
sticker, not the ability
of the technician. It was the name printed on the sticker that
brought me to the belief that a "competent" installer did the
work...a long time ago, as suggested by the faded condition of
near the ball. Okay.
some sleep. You obviously make some good points, but they don't
need to be couched in scorn.
You're beginning to make me suspect I stepped in troll feces.
Your close.... but its homeowner feces. Homeowners belong in
alt.home.repair, not here. this is a forum for professionals *IN THE HVAC
Most homeowners/slumlords come in here expecting us to tell them how to fix
their broken 30 year old, Jurassic, furnace for free, or are not happy with
their heating and cooling system that was either self installed, or
installed by the lowest bidder. They get pissy when they get told that its
going to cost them money to get it done right. They expect their system is
supposed to last forever, but they trade in their $50,000 SUV every other
year. FWIW, the chance of some 'moaner coming on here being one of *MY*
customers, or being in my service area, is about 1 in 4 BILLION.
Its kind of like the idiot that thinks they can price shop over the phone
and call asking "How much is an air conditioner??" when they don't have a
clue what they have or size or efficiency or....
Try calling a car dealership and ask them "How much is a car??". you get
Its not our problem when they get told what they don't want to hear.
I have to deal with my own customer base and tell them when its time to
replace their system....its not what they want to hear, but they know its
what they *need* to hear. They know its going to cost them $$$$$$$$ to
replace their system when its time. My customers also know they will get
their moneys worth.....they don't care about low price, they just want it
Until you can actually show somebody the difference, and the results, they
won't know whats right and whats not. You can get it done by a *COMPETENT*,
licensed, insured, professionally trained, Master HVAC Technician, or you
can get it done cheap. Its your choice.
In the mean time, please go troll alt.home repair......not here.
I read and comprehend just fine...
You again state, "It was the name printed on the sticker that brought me to
the belief that a "competent" installer"
That says you thought the installer was competent because of a sticker,
I was trying to avoid paying a bunch of money for a 5 minute visit to get
the answer to a question I /thought/ was simple. I also thought I would
be asking HVAC guys in this group what they think I should do. The
answer is obvious: hire them.
I think I'll try that attitude in comp.lang hierarchy and see how far it
gets me. Or maybe in a computer repair forum on the web: "You want to
learn how to fix your hard drive? Call a pro and give up."
Thanks for the civil answer, anyway. I'll probably do that.
You may be due some reading comprehension practice, too. There were
answers in all the natter that you missed; your jerking knee got in front
of your eyes.
Succinctly; With consumer filters, NO, you cannot reduce the size of the
filter box to the size of the duct, any more than you could stuff a wad
of cotton in your "straw" analogy, and expect to get the same amount of
air through it.
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in
question. It sort of caught me off guard.
air moves through any given area of the filter, thus increasing filter
effectiveness and life, as well as reducing the resistance to air
movement. It's the opposite of the Venturi effect.
However, I'm not talking about reducing the filter size. I failed to
mention that the filter is at the furnace. I just wanted to reduce the
opening of the pipe that leads to the filter. From the perspective of
surface area, the opening to the pipe is three times the pipe itself.
It's like a pipe hanging in a doorway. Can't I make it a pipe hanging in
I know, I know. Call a pro. Sigh.
Thank you also for a reasonable reply.
If you can figure out the effective open area of the grille that will
cover it, sure. But the grill restricts air not only by its "closed"
area, but by friction effects (The vanes "zig-zag" so the air is
deflected going through, deliberately obscuring a visual line to the open
That's why competent pros have tables and nomograms describing all that
stuff. For cosmetic reasons, nobody wants exposed elements to be bigger
than they must be. A good HVAC technician can minimize the openings
without minimizing performance.
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in
My grille is huge, with only straight vanes. I can see right in to the
duct. You are right...I don't want that ugly thing any bigger than it
has to be. I understand now why it's not as simple as I thought.
Wouldnt it be so nice if everything in this world was free. Maybe if a
company sent out a newbie and he spent an hour to answer your so
called 5 min problem, then maybe you'd feel better about paying a
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