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Old 07-26-2011, 09:59 AM   #1
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New AC & Furnace not blowing enough air


Hi, I live in St. Louis and my AC recently went out so I purchased a new AC and Furnace (since my current furnace was almost 25 years old). Unfortunately the AC is not blowing strong enough and the house isn't getting below 80-81 degrees. The tech said it may need more freon but I am concerned the blower might not be strong enough either.

The unit is a Ducane 13 SEER 2.5 Ton with 3 Ton Coil (so I am told). The furnace is a Ducane 66k Furnace (and I was quoted for a 75K furnace... so that is a bit of a concern as well).

In the end, we have some vents that are not blowing half as strong as before. Granted the previous furnace was way oversized so I assume the blower was much bigger?

In the end, I am trying to determine the easiest way to get the vents to blow more air and also have the house cool down better. Would a larger furnace come with a stronger blower? Should I request a 3 ton system instead of 2.5?

BTW the filter I am using is a brand new pleated filter (on the cheaper side) and its the same type that I used in old furnace.

Also my house is approximately 1750 sq ft which includes a basement and partial attic/room at the top which always got a little hot during the summer. But I think its even more hot now with the vent barely blowing any air up there.


Last edited by dficken; 07-28-2011 at 03:06 PM.
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Old 07-26-2011, 10:16 AM   #2
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New AC & Furnace not blowing enough air


You need to check if the blower is set to high speed in cooling mode.

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Old 07-26-2011, 01:02 PM   #3
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New AC & Furnace not blowing enough air


Is the cold air come to your room really cold ? should be at least 16-18 degrees below your room temp at that time.
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Old 07-26-2011, 01:14 PM   #4
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New AC & Furnace not blowing enough air


The first question that needs to be asked is,,,,Did the contractor that sold you the equipment do a Manual "J" to determine the load required?

System sizing depends on so much of what the variables are, for instance, condition of the windows, type of insulation, size of the individual rooms.

Did the contractor change the duct work with the installation of the new unit? and if they did, perhaps the ducting is too small.

66K sounds on the low end to me for a place with the amount of square footage that you have, but again without knowing the loads requirements it is impossible to say.

Get the contractor back, have them show you the load calculations, retain a copy of same.

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Old 07-26-2011, 02:52 PM   #5
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New AC & Furnace not blowing enough air


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You need to check if the blower is set to high speed in cooling mode.
Not to hi-jack this thread, but I am curious how do you know if it's set to high speed in cooling mode? I'm having issues of my own and I believe my blower is a 3 speed blower, but not sure how to tell if it's blowing on the correct speed....I'm wondering if this is part of my problem as well.

Thanks
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Old 07-26-2011, 03:03 PM   #6
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New AC & Furnace not blowing enough air


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Originally Posted by Master Brian View Post
Not to hi-jack this thread, but I am curious how do you know if it's set to high speed in cooling mode? I'm having issues of my own and I believe my blower is a 3 speed blower, but not sure how to tell if it's blowing on the correct speed....I'm wondering if this is part of my problem as well.

Thanks
Black wire is high speed.
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Old 07-26-2011, 03:23 PM   #7
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New AC & Furnace not blowing enough air


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Black wire is high speed.
Is it possible that the motor has issues and would sound fine, just not blow at a high speed if it's wearing out?
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Old 07-26-2011, 04:00 PM   #8
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New AC & Furnace not blowing enough air


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Is it possible that the motor has issues and would sound fine, just not blow at a high speed if it's wearing out?
I think your system is under charge.
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Old 07-26-2011, 04:41 PM   #9
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New AC & Furnace not blowing enough air


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Black wire is high speed.

Well the black wire is connected to the "COOL" terminal of the circuit board. The strange part is what is supposed to be a blue wire is a Red wire, which is connected to M1, then the diagram shows nothing on M2, but there is an orage wire connected to it going to the blower motor. Guessing it's wired correctly, hopefully it is a freon thing for me, or hopefully the tech can figure it out, but I'll stop jacking this thread!!

Thanks!
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Old 07-26-2011, 05:51 PM   #10
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New AC & Furnace not blowing enough air


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Originally Posted by dficken View Post
Hi, I live in St. Louis and my AC recently went out so I purchased a new AC and Furnace (since my current furnace was almost 25 years old). Unfortunately the AC is not blowing strong enough and the house isn't getting below 80-81 degrees. The tech said it may need more freon but I am concerned the blower might not be strong enough either.

The unit is a Ducane 13 SEER 2.5 Ton with 3 Ton Coil (so I am told). The furnace is a Ducane 66k Furnace (and I was quoted for a 75K furnace... so that is a bit of a concern as well).

In the end, we have some vents that are not blowing half as strong as before. Granted the previous furnace was way oversized so I assume the blower was much bigger?

In the end, I am trying to determine the easiest way to get the vents to blow more air and also have the house cool down better. Would a larger furnace come with a stronger blower? Should I request a 3 ton system instead of 2.5?

BTW the filter I am using is a brand new pleated filter (on the cheaper side) and its the same type that I used in old furnace.

Also my house is approximately 1650 sq ft which includes a basement and partial attic/room at the top which always got a little hot during the summer. But I think its even more hot now with the vent barely blowing any air up there.
Post pics of the furnace and the duct work. Take at least one pic that the full furnace and duct work can be seen, and then a couple closers ones so that we can see the duct attachments better.

It could be just the way the duct work is attached.
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Old 07-28-2011, 02:52 PM   #11
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New AC & Furnace not blowing enough air


Below is a snapshot of the furnace and duct work. They basically tied into the existing trunk and did not modify anything else. The furnace I had before was like 126k btu. I know it was oversized from a btu perspective but i don't think by much (considering 60% efficiency and my living space is ~1800sqft with 2 stories). All in all i think this furnace is undersized (especially from a blower perspective). And besides I was quoted for 75k and got 66k. In the end I need something with a stronger blower so it can pump that air up to the 2nd floor and at least a 75k btu unit like I was quoted. I am currently regretting that I had them replace the furnace since there was nothing wrong with it and at least it would have been able to blow up to the 2nd floor. I just replaced it since it was 25yrs old.

I am now also concerned that I was quoted for a 3 ton coil (with 2.5 ton condenser) but it looks like the coils is and ADP 15" model (HE32136D). Looking at other sites, 3 ton condensers are matched with 17" coils. Can anyone comment on this? Did I also get a smaller coil than promised?

Oh also thanks for all the replies so far. I appreciate them.

Oh x 2... no the contractor did not do a manual J and yes I am regretting that now. In the end, I am hoping he puts in the the correct larger equipment or I may just tell them to come back and take it all out.

Oh x3... the furnace vent isn't hooked up since I am not using it yet and they still have to run a flue liner. They say that will be done tomorrow...

Last edited by dficken; 07-28-2011 at 03:01 PM.
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Old 07-28-2011, 05:10 PM   #12
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New AC & Furnace not blowing enough air


A 75K furnace will have the same 3 ton blower that yours does. Most basements add very little cooling and heating loads so subtract that from the 1750 and you're heating/cooling 1000ish square feet. They might have to modify the duct work to increase the velocity. Don't get a bigger system.
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Old 07-28-2011, 05:41 PM   #13
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New AC & Furnace not blowing enough air


Quote:
Originally Posted by Marty S.
A 75K furnace will have the same 3 ton blower that yours does. Most basements add very little cooling and heating loads so subtract that from the 1750 and you're heating/cooling 1000ish square feet. They might have to modify the duct work to increase the velocity. Don't get a bigger system.
What he said.
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Old 07-28-2011, 06:21 PM   #14
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New AC & Furnace not blowing enough air


You old furnace prob ably was only a AFUE of 60%, but its steady state efficiency would have been 78 to 80%.

You would get better air flow, if they had set the furnace in the center of the supply drop, and then transitioned out toward both sides. Your return probably makes a sharp 90 into teh furnace, which also restricts air flow.

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