It sounds to me like he understood what he cited perfectly well.
BTW, if it's so damn bad to close a couple of registers, why do the
vast majority of homes have them? New construction here has
virtually every output register with a closeable flap and user
On Sun, 8 Feb 2009 05:28:55 -0800 (PST), firstname.lastname@example.org wrote:
and do you actually know trader, that if all duct systems were
properly sized and installed, you would not need a closeable flap on
them. Unfortunately, most systems are installed by the lowest bidder.
Its all driven by the builder. He builds the home, hires the lowest
bidding subs and profits at the highest sale price. This process
happens in some of the least expensive and most expensive homes
But what constitutes properly sized. You may want a bedroom warm and comfy
while I like it cool to sleep. Thus the reason to have those closeable
flaps. One size does not fit all no matter who does the install.
Which is why on a proerly designed and set up forced air heating
system you will generally find the main plenum/duct gets smaller the
farther it gets from the furnace, and not all heating duncts coming
off that main duct are the same size, AND there are balancing dampers
in at least several of those "take-off" ducts heading to various parts
of the house to balance the air flow.
In cheap contract housing you seldom see these features.
That said, if you don't want your bedroom, for instance, as warm as
the nursery or the livingroom, you partially (or fully) close off the
heat flow to that room. (whether the system was properly designed or
On Sun, 08 Feb 2009 19:11:04 -0500, email@example.com wrote:
Actually, what you describe above is the correct way it should be
done. In my area I am in homes everyday anywhere from $250K to
$2 million in value. You almost never see balancing dampers in the
main trunks nor in the supply runs. Supply and returns are usually the
same size from beginning to end. If they are stepped down it is done
just by some random method and not per actual CFM. Its quite a shame
to see that the builder dictates this so much by hiring the lowest
bidder even in the upper scale homes
And "what he cited" did not address the OP issue: whether closing
registers could damage the furnace. The study he cited, without
understanding, did NOT ADDRESS THAT ISSUE.
Clear enough for you, idiot... ?!
OK - I just hiooked up a "sensitive manometer" to my furnace duct.On
OK - I just hooked up a "sensitive manometer" to my furnace duct.
Zeroed with the furnace shut off, at 600cfm (the low constant speed)
there is no reading on the manometer. With it on normal blower speed
for heating (900cfm I believe - might be 1200)) with all registers
except the covered on in the bedroom open, there is still no reading
on the manometer. When I close 3 more registers I get about 0.15
inches on the manometer. I'd accept an error of 0.1" at zero, meaning
I MIGHT be getting up to 0.25" WC with 3/13ths (23.1%) of the outlets
The air temperature rise across the heat exchanger changes 2 degrees C
on 35000 BTU output, and aprox 4 degrees C at 50,000 BTU output.
This is a two stage 35000/50,000 BTU 80% efficiency NTV6050 ICP
(Tempstar) furnace feeding a 9X17 hot air duct with 9 takeoffs from
it, 7X 5 inch and 2X4", and a total of 14 ( I just counted them)
outlets and 3 cold air returns (one on each floor). With one
permanently closed I'm making my calcs as having 13 and closing 3-
Test equipment is a 45 degree water manometer (meaning 1 inch change
in water level in the tube is equal to .5 inch WC pressure change) and
2 thermocouple temperature guages with 0-999 display accurate to the
neerest degree C.
I am fammiliar with the operation of both instruments and repeated the
experiments 3 times with discrepencies well below 10% error highest to
Plenum output temps at 50KBTU were 65 degrees C and at 35KBTU 46
degrees C with the outlets all open and ambient (cold air return) at a
nominal 20 degrees C. Ratio of 45:26= 1.73:1
If the rated BTU output was accurate, the temperature change would be
predicted to be 50:35 = 1.43:1, so we do not have a gross error which
would indicate a seriously flawed methodology.
I think this has pretty well put the question to bed. If closing off
almost 1/4 of the airflow only raises the output temperatures and heat
rise across the heat exchanger by 4 degreec C at high output and 2
degrees C at low output, closing ONE register is NOT going to damage
the furnace heat exchanger. In my case, 1 closed instead of 3 would
produce approxemately ONE degree difference at 50KBTU with a 900 (or
possibly 1200) CFM blower.
Furnaces have a heat temp range, there is a maximum design temp for
the exchanger in your manual. Exceeding it lowers efficiency and and
most likely furnace life. It can also give you uneven heat and shorter
cycling. When the exchanger goes it is an expensive new exchanger, or
you opt for a new and maybe more efficient unit. You dont know if the
units ducts are undersized and that you may already be at its maximum
temp. One register isnt much if you have 30 but it is smartest to know
what temp you are at just above the exchanger to know what leeway you
have before closing down supplys, closing a supply restricts air and
raises the temp of the furnace. My temp was to high, I had it lowered
and heat was more even and comfortable.
There you go, missquote me. I said I had it done, Re-Read it. I had
the blower speed raised by my installer, put in 3 basement supplys, 1
new return, and increased 2 returns sizing. Now I have a low enough
exchanger temp to balance all I want. I did not recomend anything
unsafe. Is life that lonely Bubba that you now need to make up crap to
feed your ego. Lets drop it Bubba, call it a permanent truce, this is
just a waste between us and group disruptive to all. Tell you what, I
will be respectfull of you and you do the same.
ransley, its like this. As long as you only give out advice that you
truely know and understand and stop making up all those numbers that
you are pulling out of thin air, I'll be happy not to jump on your
There are 4 limit switches listed as possibilities on my furnace -
180, 190, 230, and 260 degrees F. That temperature is taken on the
wall of the heat exchanger plenum.
With 180 being the LOWEST, which is 82.2F, and 260 being the highest
(being 126C) the plenum temps in the 60 - 70 degree C range are
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