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Q: Central Air conditioner leaves basement too cold and 2nd floor too warm ( Answered 4 out of 5 stars,   4 Comments )
Subject: Central Air conditioner leaves basement too cold and 2nd floor too warm
Category: Family and Home > Home
Asked by: berkindale-ga
List Price: $100.00
Posted: 07 Jun 2005 06:46 PDT
Expires: 07 Jul 2005 06:46 PDT
Question ID: 530315
Hello, I have a two story house with a basement.  The stairways are
open style on both floors, permitting easy air flow between floors.  Two Carrier
furnaces (recent vintage- DC motors with electronic controls)
connected to two Carrier (recent vintage) AC units are used.  My problem is
the continuing shortage of cold air upstairs while the basement is
very cold.  The service company has checked it and says this is the
best equipment available.  However they are not especially
imaginative. One idea I had was to put an new air vent in basement
with a new duct (maybe hanging on the outside of the house since it
would be difficult to find an inside the wall route) routed to the
attic and then piped into the 4 problem rooms on the second floor.
This would have the effect of removing some of the cold air from the
basement and using it on the second floor. I would like to know if
this make sense, or of any other ideas to deal with this problem.
Subject: Re: Central Air conditioner leaves basement too cold and 2nd floor too warm
Answered By: umiat-ga on 07 Jun 2005 14:35 PDT
Rated:4 out of 5 stars
Hello, berkindale-ga!

 I locked your question as soon as I saw it posted. My husband has
been a building and remodeling contractor for over twenty-five years
and I thought he would be an excellent resource to help find some
resolution to your problem. I picked his brain and have transcribed
his thoughts and suggestions below.


 Many homes have duct work that is designed for heating, only. Air
conditioning requires larger volumes of air and, therefore, larger
ductwork. This might explain the shortage of cold air upstairs. It
would, at this point, be very expensive and messy to replace the
existing ductwork in your house to accommodate larger volumes of
colder air.

 You mentioned the open stairs, I assume, because you realize that
cold air is heavier than warm air and it ends up "falling down the
staircase," super-cooling your basement. It is my guess that the
return air ducts are also near the staircases, which further amplifies
this condition.

 One suggestion is to install a door in the hallway staircase to
isolate each floor. While it is normal for your top floor to be warmer
than the lower levels, the open stairs may be aggravating the

** Thus, the stairways may represent the most important component in
terms of remedying the temperature imbalance.

 It may also be possible to isolate the basement by installing a
permanent or temporary door. This would help to reduce the volume of
air in the house that you are trying to cool. I am assuming that you
are not actively trying to cool the basement. If, in fact, your AC
system * is * cooling the basement (maybe the main floor ductwork and
basement are connected), try sealing off the basement ducts during the
cooling season.

 Your idea of ducting basement air to the upstairs may not be a bad
idea. There are three suggestions that you need to keep in mind if you
decide to go this route:

* If you decide to run the ducting outside, make sure the pipe is
insulated since the sun could superheat the pipe and defeat the whole

* Make sure the ductwork splits in the attic to serve each room as far
from the stairwell as possible.

* If you have a bearing wall that stacks from the top floor to the
basement, this might provide a superior spot for the new ductwork,
rather than running it outside the house.

 Finally, go to the following website and follow the instructions to
double check that the cooling capacity for your home is satisfied by
your AC equipment.


 I hope these suggestions are helpful. Obviously, if you have gone to
the expense of installing Central Air, you want it to work properly
and efficiently.

 If you have any further questions, please don't hesitate to ask!



Clarification of Answer by umiat-ga on 07 Jun 2005 17:28 PDT
 In lieu of placing doors in the upper stairway doorcases, I wonder if
there is some sort of insulated draw-type curtain that you could use
to pull across during the day and evening. Then, you could simply move
it aside for a more open look when desired. I don't know if this would
work or not. It would have to be a heavy, insulated fabric, and hang
from the upper doorframe to the floor. It would not be as efficient as
a closed door, but might provide an easier solution to a seasonal

Request for Answer Clarification by berkindale-ga on 07 Jun 2005 18:54 PDT
Thank you for your answer. Most of those ideas I have tried, or they
don't work in my situation (the home has two stairways going to the
basement and it is impratical to use doors or curtains (and keep my
wife happy with the 'look').

For clarity on the need for more airflow to cool, is there any merit
in considering a booster fan inside certain ducts?  I have been told
they either are noisy, or will become so in time.  Are you aware of
any better designed fans of this type?

Thank you, again.

Clarification of Answer by umiat-ga on 07 Jun 2005 21:59 PDT
Hello, berkindale!

 First off, I need you to clarify some of the points I made in my answer. 

 You have stated "Most of those ideas I have tried, or they don't work
in my situation."

 I was under the impression that you had not tried any ideas yet, and
were asking for advice as to whether running additional duct pipe
outside the house and up through the roof into the upstairs rooms was
a viable idea. I gave you my thoughts on this proposal and offered
some tips on how to make it work in the most efficient manner.

 * You have also not responded to the question of whether you are
actively cooling your basement with your AC system, or whether it is
simply ice cold because the air is sinking back down the two stairways
into the basement. As I stated in my answer, it is important that you
try to seal off the basement ducts/vents during the cooling season if,
in fact,  the AC unit is actually designed to cool the basement as
well as the rest of the house. (This is especially important even if
you are against the idea of a temporary door at the bottom of the
basement stairs.)
** The fact that your upstairs rooms are undercooled is a function of
undersized ducts and/or an undersized air conditioning unit. You did
not addresse whether you have utilized the Res check link that I
provided in my answer to determine whether your AC unit is adequate to
cool the space that you have in your house. You should do this despite
the fact that your service company told you it is the best equipment
available. It may be good equipment, but it may not be powerful enough
to adequately cool your air space. The Res check site will provide
unit size information very specific to your house.

 If you find that the air conditioning units are the proper size, then
it leads to my earlier support of your idea to run additional duct
pipe. You may want to try recirulating the basement air back up to the
top floor as you initially proposed (either outside the the house and
through the roof into the upstairs rooms as you suggested, or through
a bearing wall which would be more preferable (if you have one.) The
other alternative, which is going to be costly, is to replace the
existing duct pipe in the house with a larger size to accomodate the
greater volume of cool air.

 As to the question you have raised about booster fans, I don't have
any particular expertise in this area. However, it is very important
to note that if your duct size is too small, no remote fan or booster
fan will move enough air to cool your house, even if it is placed
inside the existing duct pipe. Therefore, the addition of booster fans
is not likely to remedy the problem when the duct pipe is not carrying
enough volume of cool air to begin with.

 If your wife is totally adverse to even a temporary door at the
bottom of the basement stairs, it seems the only rememdy at this point
is to go the route of supplementary duct pipe, or to replace the
existing duct pipe entirely with a larger size. You really need to
call in a contractor who can look at the specifics of your situation
and give you some on-site suggestions. It may save you time and money
in the long run.
 My husband gave me a good analogy earlier. The design of your house,
as you have described it, is similar to a situation of one pouring a
huge bucket of cold water through the roof. Rather than having
doorways on the upper level to contain some of the cold water, it
simply rushes down both staircase into the basement. (Your earlier
question did not mention the fact that you had two stairways into the
basement, so this further aggravates this scenario.)

  Truly, without seeing the design of your house first-hand, and the
unwillingness of your wife to install temporary doors or even
insulated curtains that could be pulled back or removed during the
cooler months, my hands are somewhat tied for further suggestions. A
consulation with a heating and air conditioning contractor might be in
order before you do anything further. At the very least, the right
contractor can provide you with some suggestions for the proper size
of ductwork if you decide to run additional pipe outside your house or
through a bearing wall.

 To sum it up, you are facing one of two situations. 

1. Either your AC unit is too small, which you can determine through
Res Check -


2. your duct pipe is too small to carry the volume of air required for
adequate cooling of your house.

 In a properly designed system, the cool air coming into the upstairs
rooms would be recirculated adequately and pulled back down by the
return air system. To add to the problem, your return air vents might
be located at the top of each stairway (a common location) rather than
inside each room, which will only add to your existing problem of the
cool air quickly rushing back down both stairways before it can
adequately cool the upstairs.

 I hope this helps to clarify my earlier answer. 

 Sincerly, umiat
berkindale-ga rated this answer:4 out of 5 stars

Subject: Re: Central Air conditioner leaves basement too cold and 2nd floor too warm
From: myoarin-ga on 08 Jun 2005 09:51 PDT
I went to bed last night wondering about your problem: two open
stairwells from the second floor to the basement.  You have a
situation in summer that accentuates the normal convection current  -
cold air sinking -  as you both have described.
If the duct outlets upstairs are near the floor, the cooler air is
just slithering  along the floor under the warm air and sliding down
the stairs.
If this is the case, you might try  - as a test -  channeling the air
from the outlets up towards the ceiling in one room, just a corrogated
board "duct" in front of the outlet(s) to see what effect this has. 
If this improves things by getting the warm air out, maybe a permanent
solution in that direction could be adequate.
(How, I don't know.)

Down in the basement:  If the AC units are drawing air from the the
already cool air in the basement, this is accentuating convection
circulation.  If this is the case, it might help to have the AC units
draw air from outside the building.
They would work a little harder to cool the air, but they would stop
sucking the air in the house down to the basement.

Umiat-ga and hubbie have made the most obvious suggestion:  doors or
curtains to break the circulation.

I have a wife, too, so I understand your remark about "looks", but
maybe if it proved effective it would convince her.
A temporary test of this be curtains on the stairs hung from
spring-tensioned shower curtain rods.  The curtain material doesn't
have to be so heavy, it is not insulating, just breaking the
circulation, weighted in the bottom hem.

Good luck!
Subject: Re: Central Air conditioner leaves basement too cold and 2nd floor too warm
From: owakeil-ga on 29 Jun 2005 21:14 PDT
Hellow all, 
I have also the same problem of warm rooms upstairs and cold rooms on
first floor and basement. I did the following:
All registered are closed in Basement
All registered are almost closed on First floor. 

I thought of two solutions: 
   1. Booster Fan (I don't even know where to get them or how to install).
   2. Close-off the returns on the Second floor, and increase the flow
across the returns in the basement and first floor (to make up the
reduced flow on the Second floor). I think this will make the air
going to the second floor cooler.

Do you think #2 would help?
Subject: Re: Central Air conditioner leaves basement too cold and 2nd floor too warm
From: jiminny-ga on 12 Jul 2005 13:17 PDT
I solved the problem:
I have a 2 story house with an open stairway to the 2nd floor and a
closed door to the basement.
I have intake vents at the top of the walls above intake vents on the
floor on the 2nd floor only. The 1st floor only has intake vents at
the floor.
To solve this problem, I have done the following:
1. Put magnetic covers on all the intake vents on the 1st floor.
2. Put magnetic covers on the lower intake vents on the 2nd floor, so
the only intake to the system is from the highest point in the 2-story
house, which draws off the hot air that rises from both 1st and 2nd
NOTE: When I'm not in a cooling mode, and in a heating mode, I simply
move the magnetic covers from the lower intake vents to the upper
intake vents.
My stairway is open at the top of the stairs with a banister 3 ft.
high and 3 ft. long.
3. I installed cardboard 40 inches high, which blocks the open
banister and allows a hingeable gate, which closes off the top of the
Warm air can rise up the stairway over the cardboard barrier and the
barrier prevents the heavier cold air upstairs from going down the the
4. In the evening, I close the door on my master bedroom and it
becomes cooler than the rest of the 2nd floor.
5. In the evening, I also put my fan control to "always ON" as opposed
to "AUTOMATIC", which circulates more air to cool down the 2nd floor
before bedtime.
I work in a room upstairs during the day and its always comfortable there.
When I walk to the cardboard gate, the air feels cool and when I open
the gate and close it before going down the stairs, the air at the top
of the stairs feels warmer.
In effect, I'm preventing the cool air upstairs from going down the
stairs. The upstairs is still a little warmer than the 1st floor, but
definetely an improvement. Maybe I need a 4 ft cardboard barrier
The cardboard is wrapped around the banister post and secured with 2
plastic electrical tie-wraps on the post which allows for a hingeable
After the cooling season is over, I plan to simply remove the
cardboard and return to the open banister and stairway.
Subject: Re: Central Air conditioner leaves basement too cold and 2nd floor too warm
From: jamboogie-ga on 25 Aug 2005 08:25 PDT
I surfed my way into this discussion because I was searching on Google
for answers to a similar problem -- top floor too hot in my 3-level
townhouse. I don't have a definitive answer, but I just wanted to
share a resource I came across.

Currently, I've slightly improved but not solved the problem by
keeping all of the air vents closed in my basement (where my full-time
office is located), and about half of them closed on the main level.

The web site has a product called "Heating and
Air Conditioning Booster," a device that you put on top of the air
vent that claims to "automatically pull up to 80% more heated or
cooled air into the room. Heating and Air Conditioning Booster boosts
your heating and air conditioning system air flow with minimal energy
cost (less than a 40w light bulb)."

It costs about $45, which is much cheaper than some of the other
suggestions of doing duct work or remodeling open space with


They also have magnetic covers you can place over your air vents to
inexpensively seal them and prevent the cooled air from leaking out
into rooms where you don't want it to go.

PLEASE NOTE: I am not affiliated in any way with this company, nor
have I tried the product yet.  I just ordered it and wanted to share
it as a POSSIBLE solution for others facing this same problem.  I'll
post an update when I have had a chance to try it out. (I have ordered
other products from this company before that have been helpful for
solving other household issues.)

Sometimes you can get a discount code for this web site to save money
on your order if you search on the internet for "coupon discount code".

Good luck and hope this helps.

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