New AC Coil????????

[cdnrealtor]

Hello

I am hoping I can get some advice. I am looking at replacing the original furnace in my house. I have seen about 5 different companies. My current furnace has not given me any problems, but we are going to finish the basement, and I would like to avoid making this replacement later.

Each company that has came out has basically provided me with the same info, excpet one. Apparently the new furnace I would be getting is physically larger than my current furnace. One company has suggested that I get a larger AC coil, and plenum. They say that if I keep the current AC coil I will reduce the air flow of the new furnace. IS THIS CORRECT?

My current plenum is approx 17 inches wide, the new furnace is 22 inches wide. My AC is from 2002, and I am not planning on replacing the unit in the near future.

Can I avoid the extra expense of getting a larger coil and plenum????

Any responses would be appreciated!

[beenthere]

Probably just the model they are using.

Furnaces come in 4 basic widths.
14", 17" 20" and 22".

Depending on BTU size of furnace.

Was a load calc done. Or are they just replacing with same size.
Newer furnaces do need to move more air then older ones did.

[heaterman]

Very seldom have I run into the senario where the new unit is wider than the old one, just the opposite. Since only one company expressed a need for this alteration, check with the other companies. Some manufacturers have multiple cabinet widths depending on several factors, blower size and capacity being one of these. Make sure that the proper size furnace along with the proper size blower drive matched to your ACs capacity is being installed.

[wahoo]

Sometimes we install a larger blower than what the AC is (IE 4 ton blower with a 3 ton AC). A lot of that depends on the size of ductwork in the home. But as a rule (as mentioned earlier) most of the newer higher eff. furnaces are narrower than the older less efficient models. You need to ask some more questions about what is being installed!

[tallertech]

I am seeing A LOT of problems with undersized duct systems! You want to be very sure they are going to provide enough airflow and verify to maintain an external static pressure below the rated max (typically 0.5"w.c.). This will ultimately affect your comfort, system performance/efficiency, and equipment reliability/longevity.

If your existing plenum is ductboard, then it should be replaced anyway. Metal and in good condition - you can keep it if it's properly sized.

A lot of contractors are eager to sell the boxes (furnace/coil), but not do the homework to properly engineer the duct system/plenums because it's labor intensive and low margin work. This lonestar might be on the right track.

[cdnrealtor]

Thank you all for your responses!

I wanted to provide some more information. My current furnace is a Claire (not made anymore) it is 17 inches wide. The replacement furnace would be a goodman gmv95 which is apparently 22 inches wide. The contractor suggested that my original coil and plenum is narrow, and by upgrading to a larger coil I would get better air flow.

Is this the case, or could I get away with what I have and the new furnace???

[dash]

Too many variables and not enough facts to say.


What is the PD of the current coil,what is the ESP of the duct system,what is the static capabilty of the new furnace?


Not that you will have the answes ,but hopefully that's why they say to replace the coil.

[dan sw fl]

My current furnace has not given me any problems, but we are going to finish the basement, and I would like to avoid making this replacement later.

Can I avoid the extra expense of getting a larger coil and plenum????
Any responses would be appreciated!

Add a separate system for the basement to avoid a need for larger coil.

The requirements for a basement are unique so why try to service two different areas with one system. Don't fight nature, so to speak. If you have one system it likely needs to be zoned.

[wahoo]

I tend to lean towards the recommendations of your HVAC contractor. If your new furnace is 22" wide, and the old coil is @17" wide then the inside of the old drain pan below the coil is about 12x19" and that would restrict the airflow quite a bit. I'm assuming you are getting a 4 ton blower, and if your AC is only a 3 ton, using the old coil MIGHT work, but just go with his recommendations. If he feels it won't work properly, then change it, or suffer with what happens. He's there , we're here and yet you need to be happy with the new unit, both heating and later for cooling!