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Old 10-31-2008, 09:11 PM   #1
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Hello Gentlemen!


I'm sure you all can but i'm hoping someone will help me out! My friend (Gary)told me to ask here ...so here I go..


I recently bought my first home, it is about 1500sf. I have 12 registersin my home. (my friend says they are 6) I replaced the furnace and the central ac (2.5 ton) The problem I am having is that the air flow is very low out of the registers. Gary said it might be a return air problem and that I should measure them. One measures 12 inches and the other 9in. Does this sound reasonable? What else could be the problem for the low air flow?



So sorry for being so bad at this.
Thank you very much,


Smiles..


Kieran

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Old 10-31-2008, 10:12 PM   #2
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There are all kinds of reasons why air flow is low. Sometimes it is just designed that way.

The bottom line issue here is your house warm?

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Old 11-01-2008, 02:22 AM   #3
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The duct work might not be sized correctly.
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Old 11-01-2008, 05:34 AM   #4
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Probably a combination of undersized return and supply ducts.

If the returns are a 12, and a 9" round, your short on return air duct capacity.

Do both of them tap into the furnace directly, or to a return plenum.
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Old 11-01-2008, 12:13 PM   #5
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What size are the registers in the floor and what size is the R/A grills
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Old 11-01-2008, 05:02 PM   #6
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The bottom line issue here is your house warm?

- In the colder months (I live in Illinois) I have to turn the thermostat up to 77 or 78 to heat the house to were it be remotely comfortable. Normally I have to set it to 74-75. I have added insulation to the attic and crawl space and have replaced the screen doors and entryway doors with energy star doors.


Do both of them tap into the furnace directly, or to a return plenum.

- I believe they just tap into the furnace directly


What size are the registers in the floor and what size is the R/A grills

- I assume you meant the holes and not the covers...The register holes are approx. 4.25" x 10" (9), 4.25" x 14" (2) and a 12" x 2.5" that is underneath my kitchen cabinets. (The covers for these measure 12" x6" and 15.5" x 5.5")

The return air openings are 13.75" x 5.75" and 24" x" 12"

Thank you all for your time.. =)

Kieran
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Old 11-01-2008, 05:21 PM   #7
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Quote:
Originally Posted by Kieran21 View Post
The bottom line issue here is your house warm?

- In the colder months (I live in Illinois) I have to turn the thermostat up to 77 or 78 to heat the house to were it be remotely comfortable. Normally I have to set it to 74-75. I have added insulation to the attic and crawl space and have replaced the screen doors and entryway doors with energy star doors.

Eithr you have poor blood circulation. Or, your house has a high infiltration rate. And you need to fix that, and or add a humidifier.


Do both of them tap into the furnace directly, or to a return plenum.

- I believe they just tap into the furnace directly

Tappe directly in to thr furnace. Without a round to square/rectangular transition, you get a lot of turbulance, which causes lower air flow.


What size are the registers in the floor and what size is the R/A grills

- I assume you meant the holes and not the covers...The register holes are approx. 4.25" x 10" (9), 4.25" x 14" (2) and a 12" x 2.5" that is underneath my kitchen cabinets. (The covers for these measure 12" x6" and 15.5" x 5.5")

The return air openings are 13.75" x 5.75" and 24" x" 12"

Thank you all for your time.. =)

Kieran
Are the supplies just tapped into the plenum, or is there a main trunk line.
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Old 11-01-2008, 05:25 PM   #8
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First off I would look at the ducts and take a complete inventory of all the ducts leading to your vents. Floor vents are only an issue of you have large pipes leading to small vents. What is important at this point is that you find the size of the pipes.

While you are at that see if there are any leaks in the vents or pipes leading to the vents.

Did you replace the furnace or did you have someone else do it?

Also pictures of the furnace with the pipes coming out it it would be good.
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Old 11-01-2008, 05:57 PM   #9
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Are the supplies just tapped into the plenum, or is there a main trunk line.

-
Sorry There is a main trunk line, I get confused easily. =) The furnace is roughly in the middle of my house, so the trunk line goes two ways from the furnace.


While you are at that see if there are any leaks in the vents or pipes leading to the vents.

-I tried to do that any could not see any noticeable gaps, tears, leaks, disconnects or anything else. I did this while the furnace was on also. I will take another look.


Did you replace the furnace or did you have someone else do it?


- I had the furnace and AC replace by a professional. The old furnace had low air flow also. (but was installed with the house in 1957) I figured a new furnace would remedy the problem but it didn't.. About a month or two after he installed it, I called and complained about the low air flow. He came over and adjusted the speed of the fan to what he said was the fastest speed he would recommend, but it didn't help. I called again about it and told him again of the problem, he mentioned something about 8"inch supplies instead of 6". He is due back at my house Wednesday or Thursday of this week.


Also pictures of the furnace with the pipes coming out it it would be good.
- I will try and get some pictures. Anything specific besides the pipes?

Thanks!

Kieran
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Old 11-01-2008, 06:19 PM   #10
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Your main trunks may be undersized.

Can't tell from here.
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Old 11-01-2008, 06:44 PM   #11
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Your main trunks may be undersized.

Can't tell from here.

My trunk line sizes are:8" x 16" x 22' (maybe 23') w/ 7 separate supplies, one branches from another (the small kitchen supply) so 8 total.

and 8" x 16" x (approx) 8' with 4 separate supplies

All supplies are 6"

Thanks! =)

Kieran
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Old 11-01-2008, 07:18 PM   #12
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Quote:
Originally Posted by Kieran21 View Post
- I had the furnace and AC replace by a professional. The old furnace had low air flow also. (but was installed with the house in 1957) I figured a new furnace would remedy the problem but it didn't.. About a month or two after he installed it, I called and complained about the low air flow. He came over and adjusted the speed of the fan to what he said was the fastest speed he would recommend, but it didn't help. I called again about it and told him again of the problem, he mentioned something about 8"inch supplies instead of 6". He is due back at my house Wednesday or Thursday of this week.
Kieran
This is your problem. A 6 inch pipe will allow enough air to heat an average bathroom and not even come close to heat a bedroom. A minimum of 7 inch pipe would help out.

A 6 inch pipe is good for about 110 cfm.
A 7 inch is good for about 200 cfm
An 8 inch is good for about 300 cfm.

In the average living room you would need 2 7-8 inch supply lines.

I see this a lot. A small furnace that wasn't cutting the mustard. I put in a larger furnace and the distribution system can't handle it. I always tell the people that their ducting system won't handle the volume of the new furnace. Most say they will change it out later when they can afford it.

They call me back a lot sooner than they plan to since the find the new furnace made little change to the system.
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Old 11-01-2008, 08:52 PM   #13
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Marvin Gardens,
Thank you for your reply.

As I gathered from your post, my supplies are too small. So if I run 8 inch supplies.. this will in fact help the air flow problem? And in doing so, will I have to increase my trunk line also? What about the Return Air?

Just some FYI:
My Father has the same size house as I do and has none of the issues I have. The same person put both new furnaces in. His is a 85% and mine is a 90+% furnace. His AC unit is 3 ton vs. my 2.5 ton. He runs what he calls a "spider" vs. my trunk line.

In my house, Each bedroom has 2 six inch supply lines, the bath one. My living room which is 21' x 12' has 2 six inch supplies.

Thank you!

Kieran
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Old 11-01-2008, 11:23 PM   #14
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Quote:
Originally Posted by Kieran21 View Post
Marvin Gardens,
Thank you for your reply.

As I gathered from your post, my supplies are too small. So if I run 8 inch supplies.. this will in fact help the air flow problem? And in doing so, will I have to increase my trunk line also? What about the Return Air?

Just some FYI:
My Father has the same size house as I do and has none of the issues I have. The same person put both new furnaces in. His is a 85% and mine is a 90+% furnace. His AC unit is 3 ton vs. my 2.5 ton. He runs what he calls a "spider" vs. my trunk line.

In my house, Each bedroom has 2 six inch supply lines, the bath one. My living room which is 21' x 12' has 2 six inch supplies.

Thank you!

Kieran
What are the sizes of your trunk lines and what is the GPM of your furnace?
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Old 11-02-2008, 08:51 AM   #15
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For a simple test, defeat the furnace blower door safety switch with a piece of tape. (keep children and small pets out of the furnace room with the door off) With the blower running check the air flow at the supply outlets with the door on and with it off, is it better or worse?
I'm betting better, because I think you need way more return air, my 2 cents

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