Even here in Alabamastan, a well insulated 2 story home can be cooled
by a 2 ton AC unit, it's all about heat load. I have one customer who
has a new home and the upstairs heat pump is larger than the downstairs
unit, why? Because the upstairs has some very large windows that reach
all the way to some very high ceilings.
On Jul 23, 6:39 am, email@example.com wrote:
Its possible he requires a 5 ton system for his 1700 sq ft. if he
lives in south Florida or southern Arizona and has little or no shade,
alot of glass facing south, and minimal attic insulation. But hes
going to need more than 7 supply registers to get the 2000 cfm out
assuming `14x6 " registers (or smaller) . The return is also going to
be a factor too as they most likely undersized that too. I see it all
the time even in very expensive homes over $1 million . Its amazing
what they get away with.
1. Because the room size (load) might require more airflow than what
one register can deliver . 2. Because the room may be configured to
where a single register wont distribute the air well enough . 3.
Because the heat gain of the room might require multiple registers to
deliver enough conditioned air to satisfy it. 4. Because one
register might be too noisy if youre trying to push too much cfm thru
it . 5. Too be sure youre moving enough air over the cooling coil
to prevent freezeup especially during low load on the system.
So that the system heats and cools evenly. I just took a quick count
of my house. I have 22 outlet vents. That's in a house that's 3100
sq ft, 4.5 ton AC. Seems about right to me. So for a house of
1700 sq ft, I'd expect around 12, not 7. Several of my rooms have 3
registers each. Every house I've ever lived in, including small
single story ranch, have had at least some rooms with more than one
Having 5 tons of AC with 7 vents just ain't Kosher.
Return air configurations come in a variety of ways. 1. There is the
ONE huge central return air grille often put in the second floor
ceiling at the top of the stairs which is ducted back to the Air
Handler. 2. There are TWO large return air grilles...one on the
first floor ceiling and one on the second floor ceiling...both
ducted. 3. A number of return air grilles placed high on the inside
walls of both downstairs and upstairs and ducted back. 4. A return
air grille in EACH room (except the bathroom) and ducted back. In
order to know if the return air duct system was properly sized, youd
have to have a knowledgeable professional come out to determine the
size(s) and how much each return air duct can handle in cfm airflow.
I can tell you this fairly accurate rule of thumb : The return air
duct area feeding a 2000 cfm (5 ton a/c system) such as yours,
requires One 18" dia. round duct or Two 14" dia. round ducts (or
equivalent retangular ducts in sq. inch area) . Hope this gives you
a bit more insight. In addition, you need to make sure your air
filter(s) , cooling coil surface , blower wheel ...are all very clean
in addition to the system being full on freon and working properly .
Ideally, you should bite the bullet and have a professional come out
and thoroughly examine the entire system and equipment. Regards.
Unit seems too big with too few supply ducts. Where are you? Duct
work in the attic or under the house? Ducts shared by the heating
system? What and where is the return duct? How long has the unit
been in place? Has this always been a problem or is it a recent
Where are you located? How old is the house? Is the bed room facing
South other than furthest from a/c unit. IMO, you have an oversized unit
for the size of house. BToo big a unit is nno good for optimal
effciency. Idea of bigger is better in a/c unit is wrong.
Are ducts insulated, I did mine and it made a big difference. Have you
tried running the fan continously, I do that on hot days and nights it
makes maybe a 3f difference in balancing it over 24 hours. Do you have
any vent dampers on the air handler-furnace. I put them in to get a
more balanced heat and AC, but be carefull you dont want to cut air
much to other rooms or you risk freezing the coil. On one long weak
run I had a bigger insulated duct and a larger vent to reduce
resistance and get more airflow. A window AC would do it today to get
you cooler, but there maybe several small jobs that could balance you
out fairly closly, just the fan on continously and a small adjustment
to floor registers might help alot. Everyone saying 7 isnt enough
isnt true, size is what matters not the number of them, if it wasnt
enough for airflow you would have frozen the coil and had no AC many
times before, till you thawed it out. Insulating can be easy to do for
two people, vent dampers are easy to install Diy. While you are at it
if you cant examine the interior AC coil cut in a hole in the ducts
and make a cover so you can look at it, it needs to be clean and mold
free or performance suffers and electrical costs can go way up. To cut
a hole you must know exactly where the coil is so you dont ruin it. Is
this house in a hot unshaded area, because that is a very large AC for
your sq ft, does it cycle alot on the hottest days or run near
continously, it should run continously if its not oversized on the
hottest days to remove the most humidity, an oversized AC wont run
long enough to cool the farthest run so running the fan continuosly
might be needed and worth a try .
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