Discussing Manual J Sizing Calc with HVAC Installer

[kyler]

Thank you all for your responses earlier related to my concerns over installing undersized equipment. I think I am going to go with the smaller 2 ton condensor and see if I can make any improvements to the existing ductwork without tearing the house apart. It also seems like 15 SEER vs 16 might make more sense as well.

I am meeting with my installer tomorrow to go over the manual J-sizing but don't know much about the calculation except that it tells me what size cooling and heating system I should be running.

Are they any questions I should be asking him when I go over the calc (I know this seems silly to some but I don't know much about HVAC)?

Also I heard the systems need to match in output (i.e. if I have a 2 ton condensor but the furnance is 3 ton is that a problem)?

[DGIO-Not]

The best advice I have is to download this and have it printed at meeting: https://www.acca.org/Files/?id=177.

And do not be afraid to go down the checklist and ask if it applies to you or not. Checklist is pretty good on explaining things, what you aren't clear on...then it is a great question to ask your contractor you are considering, they should definately not feel uncomfortable in discussing these things.

[bryantman21]

on the matching size, the indoor evap needs to be at least as big as the outdoor unit but having a inside coil that is one size larger will work the biggest advantage to that is you will get better dehumidification it usualy will help some with your seer rating.

[NY2GA01]

on the matching size, the indoor evap needs to be at least as big as the outdoor unit but having a inside coil that is one size larger will work the biggest advantage to that is you will get better dehumidification it usualy will help some with your seer rating.

I thought there could only be a half ton difference between outdoor coil and the indoor coil.

I will have to check on that one when I get to school tomorrow.

I also thought that if the seers do not match up that you will only get the value of the lowest rating. So if you have a 13 seer indoor coil and 10 seer outdoor unit, I thought you would only get the value of the 10 seer

I will have to check on that one tomorrow as well.

I have the program director for two classes this semester, so I will see what he has to say.

[bryantman21]

Going a ton larger is just fine with all manufactures I have delt with. As for the seer rating a 16 seer unit for example, that's the best case scenario rating but if you look up the ahri ratings for a condensor evap and blower unit together you usually don't hit the max seer rating and a larger evap can help with that ( not all cases).

[btuhack]

Equipment is rated at 80* indoors, so if you expect to maintain a lower temp, now would be the time to bring it up.

[hvacvegas]

Tonnage doesn't matter on the coil.
Instead of using a rule of thumb, just look up the rating (as bryantman has said) with AHRI. Thats the best way to determine if a coil is rated.

Bryantman, there are some that would argue your statement about having a large coil providing more dehumidification is incorrect.
The idea with a "normal" sized coil would be a lower coil temp, thus being much more below the dew point, thus providing additional dehumidification.

[hvacvegas]

I thought there could only be a half ton difference between outdoor coil and the indoor coil.

I will have to check on that one when I get to school tomorrow.

I also thought that if the seers do not match up that you will only get the value of the lowest rating. So if you have a 13 seer indoor coil and 10 seer outdoor unit, I thought you would only get the value of the 10 seer

I will have to check on that one tomorrow as well.

I have the program director for two classes this semester, so I will see what he has to say.

ARI: 4594726

Thats a ASZ18036, (3ton)with a CAPF4961 coil. One could say that the coil is "rated" up to 4-5 tons. On top of that, the odd numbers indicated it's a beefy coil. Has an extra row. 18 seer rating.

ARI:3068859

Thats a SSZ14036, with a ASPF4260 air handler. One could say that the coil in the air handler is rated for 5 tons. 15 seer.

The old way of thinking, was: Find AC tonnage. Find a coil of the same tonnage, that would fit in the plenum. Don't worry about seer.

Things have changed. Just because the "tonnage" is the same, doesn't mean that your going to get the correct seer out of the unit. You can usually get away with that method if your just slamming in 13 seer equitment, but you still have to watch out.

For instance, an ASZ18036 (18seer 3ton) won't match up with a CAPF3636, even though they are the same tonnage.

[bryantman21]

Maybe I am thinking wrong but larger coil larger txv and orfice, the more freon that can boil off giving you a more constant coil temp under high load?

[tedkidd]

Carrier bryant matches coils up to 1 extra ton on communicating equipment. More surface area gains a little efficiency. May also grab a little moisture, irrelevant with evolution since it dehumidifies so well. If that unit doest keep the house comfy you need a separate dehumidifier.

[dan sw fl]

The best advice I have is to download this and have it printed at meeting: https://www.acca.org/Files/?id=177.

And do not be afraid to go down the checklist and ask if it applies to you or not. Checklist is pretty good on explaining things, what you aren't clear on...then it is a great question to ask your contractor you are considering, they should definately not feel uncomfortable in discussing these things.

https://www.acca.org/Files/?id=186

[kyler]

The best advice I have is to download this and have it printed at meeting: https://www.acca.org/Files/?id=177.

And do not be afraid to go down the checklist and ask if it applies to you or not. Checklist is pretty good on explaining things, what you aren't clear on...then it is a great question to ask your contractor you are considering, they should definately not feel uncomfortable in discussing these things.

Thanks Designer Dan. This is a great checklist. I will go over this with my contractor tonight.

[kyler]

Thanks for all the advice. I will make sure the equipment is AHRI rated and discuss it with the contractor to make sure the coil and condensor match up properly for the best ratings.

Any comments on the gas furnance tonnage matching up with the coil and condensor? Do they have to be the same. The current proposal has a 2 ton condensor and hopefully a matching coil with a 3 ton 60K BTU variable speed two stage A/S 96.7% furnace. The coil and condensor are also American Standard (Allegience 16).