I was given a newer Carrier central air unit ("N" coil and Condenser, etc.). The problem is that I have a Lennox furnace and the "N" coil is slightly smaller than the plenum opening above the furnace. If the "N" coil was installed there would be a lot of air bypassing the coil.
Do I need to get a specific sized coil to match the make of the furnace?

I`ve worked on some units in the past and I found this to have happened before. What they did was to use sheet metal and filled in the sides of the furnace that wasn`t covered by the evap.coil and by doing that all the forced air had no choice but to go through the coil and not around it. It seemed to be working pretty well with no complaints from the home owner

Put a access door on that carrier N coil. They have been known to have leak problems unless they have fixed that problem by now.

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Originally Posted by hvac1000

Put a access door on that carrier N coil. They have been known to have leak problems unless they have fixed that problem by now.

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My concern is "choking down" the furnace plenum by sheet metaling to get all the air through the coil.

Some newer style coils are smaller than the original and some are larger. If the coil has a size tag and it is a 2 ton coil it will do 2 tons of cooling etc. You have provided no pictures so it is difficult to tell exactly how bad this chocking problem might be ot if you need to install turn/vanes ora tapered system to have smooth air flow. Take some pictures and post them. We will have a look see.

Quote:

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Originally Posted by hvac1000

Some newer style coils are smaller than the original and some are larger. If the coil has a size tag and it is a 2 ton coil it will do 2 tons of cooling etc. You have provided no pictures so it is difficult to tell exactly how bad this chocking problem might be ot if you need to install turn/vanes ora tapered system to have smooth air flow. Take some pictures and post them. we will have a look see.

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Thanks I will do asap...

Quote:

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Originally Posted by hvac1000

Some newer style coils are smaller than the original and some are larger. If the coil has a size tag and it is a 2 ton coil it will do 2 tons of cooling etc. You have provided no pictures so it is difficult to tell exactly how bad this chocking problem might be ot if you need to install turn/vanes ora tapered system to have smooth air flow. Take some pictures and post them. we will have a look see.

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Photo attached (I hope) of furnace insides.

Here are dimensions:

Furnace plenum:
Depth 20"
Width 21.25"

Coil:
Depth 18"
Width 14.5"

Thanks!

You will have to pan in the area so the new coil has something to sit on. The coil cabinet/plenum seems to already have a access door so that is a good thing.

Now if it were me I would build or have built a taper seat or perch for that new coil. This will elevate the coil some but would make for smoother air transfer across it. This would also help eliminate any choking of the air flow.

One other item to consider is to use a larger coil for a 3 ton system. I have no idea what that size would be but it might have a larger base. If you went that route you would just use the same size flow rater/piston/or expansion valve as the 2 ton coil would use. It will give a larger wet surface area and would also help with moisture removal.

You are not a pro at this so you might seek some advise from where you bought the equipment since there are options to be considered and a perch or panning to do so the coil will fit properly.

I am not there and I do not do drawings/design work here so all I can do is give you good advice and ideas.

Quote:

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Originally Posted by hvac1000

You will have to pan in the area so the new coil has something to sit on. The coil cabinet/plenum seems to already have a access door so that is a good thing.

Now if it were me I would build or have built a taper seat or perch for that new coil. This will elevate the coil some but would make for smoother air transfer across it. This would also help eliminate any choking of the air flow.

One other item to consider is to use a larger coil for a 3 ton system. I have no idea what that size would be but it might have a larger base. If you went that route you would just use the same size flow rater/piston/or expansion valve as the 2 ton coil would use. It will give a larger wet surface area and would also help with moisture removal.

You are not a pro at this so you might seek some advise from where you bought the equipment since there are options to be considered and a perch or panning to do so the coil will fit properly.

I am not there and I do not do drawings/design work here so all I can do is give you good advice and ideas.

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Thank you!

If I understand correctly it would be a tapered perch forcing all air through the coil - correct?

Yes that is what I call it but I am an old man. I am sure there are different names for it but a old sheetmetal guy will understand.

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Originally Posted by hvac1000

Yes that is what I call it but I am an old man. I am sure there are different names for it but a old sheetmetal guy will understand.

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Thanks for your help!

Can I use regular plumbing silver solder for the copper supply lines?

Only Braze the copper lines. I am not cheap so I use 15% stick but other % will work. Also you should have a little nitrogen flow while brazing and protect all valves etc with Zorba the Heat or wet rag to prevent any damage.

See some links here

Proper brazing copper lines - Google Search=