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Old 09-15-2008, 02:31 PM   #1
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Help with return and supply size




I have a Heil N8MPL125J20 5 Ton 125000 BTU unit istalled in my home just pryer to my purchasing of the home.

While remodeling I found out that the supply ducting was cardboard and had collapsed making it useless. The return air was left open to the crawl space under the house causing the musty smell of the dirt below to come up through the vents.

What I need to know is how much sealed return will this unit need and what size should the supply ducting be.

Thanks

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Old 09-15-2008, 03:10 PM   #2
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Help with return and supply size


So your furnace was set over a hole in the floor and then it goes nowhere!? You do have other holes in the house (in other rooms) that are cut into the crawl space?
Where did the supply air duct come apart? Its card board? You sure its not duct board?
Let us know we will try and help....... j

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Old 09-15-2008, 04:39 PM   #3
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Help with return and supply size


So your furnace was set over a hole in the floor and then it goes nowhere!?

The furnace was installed over a boxed enclosure in the garage. One vent was boxed and ducting went to the enclosure. The other vent had plumbing and wires going though it, so that side was left open to the crawl space.

You do have other holes in the house (in other rooms) that are cut into the crawl space?

There are floor vents, is that what you mean?

Where did the supply air duct come apart? Its card board? You sure its not duct board?

Its probably duct board. When I looked at it just looked like a cardboard pipe. It appears it was weakened by moisture and fell apart at several points where the supports were. I would like to replace it all with flexible insulated polyester ducting, seems affordable and much better, but I need to know what size.


Let us know we will try and help......
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Old 09-15-2008, 06:12 PM   #4
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Help with return and supply size


I'm sorry I think there is too much wrong here. Pipes in the R/A and its wood! If the furnace was installed over a boxed enclosure in the garage There are strict rules to that.
A 5 ton furnace A / C would need a R/A area of 350 sq/in the S/A would be about the same. I think you need a HVAC help in your city because wile you may be able to do the work a photo is worth a 1000 words
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Old 09-15-2008, 10:16 PM   #5
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Help with return and supply size


OK I am going to try to give the full pictorial here, lighting was a challenge so I appoligize if this is a little hard to see.

By the way, thank you very much for the help!

Here is the front view of the furnace in the garage, I cannot tell what all the box is made of, but the top is definately plywood.

Next the view from the front of the box. One 12" return in a wall can partially blocked by 2 X 4.

The other return is open as I hope you can see in upcoming photos. I am showing the inside vents next.

This is both vents side by side. The can I put there to show it was a sealed on the left return to the connection showed in the previous picture.

Next the right vent, blocked by wire and plumbing.

Now in the crawl space.

This is what was used as the secondary return. The open section at the bottom leads to the left side of the garage box from the previous picture.

This a view of the supply duct leading away from furnace. About half of them have collapsed at the supports and there is no insulation as best as I can tell.

This is the view leading to the furnace, showing the collapse and the ducting.

Sorry I am maxed out on photos.

I was quoted $4700.00 to do this work and it seemed very high. My rough estimate of materials was less than $700 to seal off the box, seal off the return and run all new premium return ducting with mastic sealing on everything.

I could just be extremely naive but being near the end of a difficult and expensive remodel this unexpected $4700 is a hard to swallow.

Please let me know if I am being unrealistic
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Old 09-15-2008, 10:30 PM   #6
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Help with return and supply size


Felt this needed to be added as well. This is only for the downstairs climate. The upstairs has a dedicated furnace and AC that I have checked out and that appears to have no leaks or problems.

The house is 3200 sq ft and this downstairs unit seems way to much but it is what I have and it is less than five years old as best as I can tell.
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Old 09-16-2008, 09:53 AM   #7
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Help with return and supply size


Well from looking at the pictures you have many problems with the way things are installed. First thing is how far is the coil on the top of the furnace overhanging the furnace? Could inpead air flow.

The duct system is a complete mess. Without putting in the size of duct for the return air it looks like it is grossly undersized for the size of furnace you have. I couldn't tell from the supplies how they were sized either.

Looking at it from a company standpoint, I think there price was low. All of the ducting looks like it needs to be resized and redone. If you use flex duct as you want to it needs to be even larger. The best way to do this is to run a manual D calc. and size the duct for the static pressure desired. It is not as simple as this size for this furnace. It has to do with CFM and static pressure. I would have it repaired by a contractor who does this all the time and knows what there up against. If you have a contractor do this you will want a warranty that it will work so the proposal you recieved is more than likely taking things further than you think they need to go to get it done right.
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Old 09-16-2008, 11:52 AM   #8
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Help with return and supply size


Quote:
Originally Posted by hvac122 View Post
Well from looking at the pictures you have many problems with the way things are installed. First thing is how far is the coil on the top of the furnace overhanging the furnace? Could inpead air flow.

The duct system is a complete mess. Without putting in the size of duct for the return air it looks like it is grossly undersized for the size of furnace you have. I couldn't tell from the supplies how they were sized either.

Looking at it from a company standpoint, I think there price was low. All of the ducting looks like it needs to be resized and redone. If you use flex duct as you want to it needs to be even larger. The best way to do this is to run a manual D calc. and size the duct for the static pressure desired. It is not as simple as this size for this furnace. It has to do with CFM and static pressure. I would have it repaired by a contractor who does this all the time and knows what there up against. If you have a contractor do this you will want a warranty that it will work so the proposal you recieved is more than likely taking things further than you think they need to go to get it done right.
I'm with you on this one, WHO ever installed this mess needs to be run out of the business!
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Old 09-16-2008, 08:26 PM   #9
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Help with return and supply size


Total Hack job!!.. I understand you want to save some bucks but it is very obvious that this work was not inspected and will need some fairly good overhaulin to make it work properly. Get a couple of quotes forma reliable contractor and get 'er done the right way.
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Old 09-17-2008, 12:13 AM   #10
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Help with return and supply size


I can see this is right now after looking and getting your input and doing my own research.

I am glad to have this this site as a resource so I didnít go off on my own rolling around in the mess trying to fix something that could not be fixed by me.

This house has been one nightmare after another and I think I have run into almost everything that can go wrong from mold remediation and screwed up drainage to this Frankenstein job.

Once again, I now know what to look for myself rather than trust the next guy waiting for me to write his check.

Hopefully this will benefit my sons when they are ready to buy a home.

Thanks

While it is going to cost me at least I know enough to make sure it is right.

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