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Old 07-22-2008, 09:09 PM   #1
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Home won't cool -- Not enough airflow

I will start by saying I am not a HVAC expert - in fact, quite the opposite.

We live in a home (ranch on a finished basement) that's about 25 years old. When the home was built originally, one end of the house was on a thermostat upstairs, the other end of the house was on a separate thermostat located towards the other end of the house upstairs.

Last year, it was suggested to me to reduce energy costs, we move one thermostat to the basement, and therefore not heat/cool the basement as much as the upstairs. Sounded like a good idea at the time.

I had my uncle come move the thermostat to the basement and I proceded to re-arrange all the duct work to make this possible.

We have a pretty large unit that runs the upstairs (I am not sure of the tonage) and a smaller unit that runs the basement. Since we have a pretty long run from the big unit to the other end of the house, my uncle suggested I make the main run 12" to accommodate for such a long run with multiple registers, then I split off to 10" X8"X8" "Y"'s + flex to the registers. The run from the unit to the kitchen is about 40 feet.

What I discovered after all this is that we now have extremely poor airflow in the den and kitchen next door. With summer heating up, it will no longer cool the far end of the house and temps in the kitchen and living room have been about 81 degrees. Back of the house (immediately above unit) cools fine, and air temp coming out of all registers has been about 59 degrees with outside temps about 95 here lately. Thermostat is in middle of house in den, and consistently reads at least 77 or above.

I added a booster fan on the line coming to register in den, and it did absolutely nothing to help air flow - Nothing! I took it out.

I have now removed the 12" and reduced to 10" and there is a little bit of improvement, but not much. Above temps are after switch to 10" main run.

IS this enough info to make any suggestions? ANY help would be greatly appreciated - we're melting and electric bill is $475+!!!!



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Old 07-22-2008, 10:32 PM   #2
oops, did I do that!
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Any chance you can put things back the way they were? It might be a good idea to find out how much air your air handler/blower is capable of moving, before you change any more ductwork.

You may want to pick up a ductilator at a local HVAC supply house.

After you figure out how to use it, you may want to punch your uncle in the nose.


Last edited by 8 Ball; 07-22-2008 at 11:15 PM.
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Old 07-22-2008, 11:16 PM   #3
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Your description is complex, confused in some parts, and lacking emough information to make a suggestion. We need to start with a system layout drawing. Make the drawing as if you are looking down on your house. Maybe you should make two drawings - one for the top floor and one for the basement. Show the HVAC unit(s) and the inteconnecting duct work with duct sizes and type (metal/round/rectangular/flex). Show the house and room sizes. Show the HVAC unit manufacturer, model, and tonnage - there should be a data plate on the unit, but if not, then show what you know. The drawing(s) do not need to be very neat , but clear and complete.

If your system cooled your house before, it can be made to do it again.

P.S. Several of your comments suggest a leaking or obstructed duct system. Put your Fan switch in the ON opposition and check for air leaks in the duct system. If one section has no air flowing (or very low), that section may be leaking or obstructed. If you have flex duct, check that no part of it is crushed or pulled tight around a bend.

Last edited by rosehillraymond; 07-22-2008 at 11:24 PM.
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