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Discussion Starter · #1 ·
Hello, we had a new furnace put in on Tuesday and would like to redo the ducts to match the new furnace can anyone help with a drawing using the info that I would give you, we can't find anyone around where we live to help us out, all they want to do is put the new furnace in make sure it works and see ya.
 

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Just can not imagine any company installing a new furnace and not connecting it to the ducts.
We have no pictures, no location, no make, model of the furnace.
Where"s around here?
 

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You should be calling your installer for this. What makes you believe that the ducts don't match?

Every duct system is different.
 

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Discussion Starter · #4 ·
They did connect the furnace to the existing ducts but did not check the existing ducts to see if they were the right size to match the size furnace they installed. Then old furnace was 70,000 btu's with 90% efficient and they new furnace is 60,000 btu's and 96% eff. so I would like to put new ducts under my home to match the new furnace so it can heat/cool the home as efficient as it should
1200 square home in central ohio
the furnace is a Goodman # GCSS960603BNAA Natural gas
and here is the set up now Text Pattern Diagram Pattern Line
 

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Discussion Starter · #5 ·
The main square duct supply is 8x8 and the longest green duct is a 14" flex duct coming out of the furnace to the plenum and where it goes under the main supply it is smashed about to 10"
 

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i remember the picture.

Every duct system is different and the installer is supposed to check the temperature rise + adjust the fan speed to get proper airflow.

If you have concerns about undersized ducts, you don't just get them enlarged, you do some testing.

You should do a temperature rise test, measuring the supply air temperature 1-2 feet away from the furnace and return. Subtract supply from return and compare it with the rated temperature rise. On a modern furnace you should be shooting for 45-55f ideally.

If it's off you need to clock the meter (google how) to make sure it's not underfired or overfired. Incorrect fuel input needs to be corrected, then the fan speed gets adjusted to get proper temperature rise.

There are also static pressure tests that should be done if you're not getting enough airflow at the maximum blower speed available for heating.

Bottom line is that you could potentially waste a lot of money upgrading ductwork when small changes can make an enormous difference. Re-doing sheet metal air ducts is very, very expensive, difficult to do in a nice basement, horrible in a crawl space/attic.

The diagram doesn't have the branch duct sizes specified. The 8x8 and 16" main feed are probably both bottlenecks, but i'm no pro.

Resi duct calculator (http://efficientcomfort.net/asp/ResDuct_Web/ResDuct_Web.asp%5C) shows the flex trunk being good for 800 cfm and a 60 000 btu 96%+ furnace will want to move 900-1000+. Now, bumping up the fan speed above the factory setting to compensate may do it.

Typical 60000 btu furnace may have a blower moving 1200 cfm on properly sized ducts, have small ducts and it may move 700-1000 on high depending on how undersized the pipes are. 700 would be the extreme with really, really crappy ductwork.

oh, got a/c? if yes, what size?
 

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Your new furnace has a slightly lower heat output than your old one, although modern furnaces tend to have higher airflows and lower temperature differentials. Did your old furnace heat the house evenly and adequately? Are there leaks in the ductwork? You need to answer these questions before you go ripping the old ductwork out and replacing it (which is probably unnecessary).
 

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A 14" flex is too small for a 60,000 BTU 96% furnace. Should be a 16", and of course not crushed.

The 8x8 for the bedrooms and living room should be 8x14, should be okay with 8x8 for the kitchen and bathroom.
 

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Just can not imagine any company installing a new furnace and not connecting it to the ducts.

Read the post, the post says they installed the furnace and connected the old ducts.

We have no pictures, no location, no make, model of the furnace.

Location doesn't changes the size of ducts.

Where"s around here?
Doesn't matter. No good company will come out and design a new duct system for free. And most don't want to invest their time for a small project.
 

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Doesn't matter. No good company will come out and design a new duct system for free. And most don't want to invest their time for a small project.
The typical customer gets shafted by typical contractors selling equipment, not looking at air ducts. typical customer is also a his or her own worst enemy, thinking a furnace is a commodity product like a fridge or tv.

just the way things are i guess.
 
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