Maybe I need to downsize my unit ?? (Had a heat calc done) Very strange...

[sb023]

So, you might have read my other posts about having trouble with my 5 ton unit freezing up and having small return/supply plenums.

Well, some guy came out today and had a heat load computer program that plugged in my windows, insulation, house size, house orientation, shingle color, etc... and he said I only need 3.3 tons !!

WTF...Maybe that is my problem.

Wow, I have a 2680 square foot house so I thought I needed a 5 ton...

Basically, he said it looks like the return/supply plenums and the heat load calc are sized for a 3-4 ton unit, so maybe the 5 ton is having problems because it is overkill and can't breathe thru the current ducting.

He said for a 5 ton unit it needs 2000 cfm minute airflow and my supply plenum using his ductulator only will push 1300 cfm a minute.

So, even increasing my return size apparently won't help because the supply can't really push out anymore anyhow.

Does this sound right, maybe need to downsize my unit? :anyone:

[amd]

Yup - you need to downsize.

A 5 ton unit will short cycle, not remove enough humidity, and have a short lifespan.

[beenthere]

sq ft doesn't indicate what size A/C you need.

[Airmechanical]

fix your ductwork

are you sure the design temps for the load calc were dialed in correctly

why don't you post the heat load calc

oversizing is bad, undersizing can be worse



.

[papa_jo]

fix your ductwork

are you sure the design temps for the load calc were dialed in correctly

why don't you post the heat load calc

oversizing is bad, undersizing can be worse



.

yea, but better to be under alittle than oversized- IMHO

[sb023]

I can't post it because the contractor had it on his computer.
Maybe I could see if he would print it but I doubt it ?

I just thought of something interesting though. He mentioned my supply coming out of the top of my air handler was too small to push the 2000 cfm a minute that a 5 ton requires but the supply plenum is the same size as the opening on the top of the air handler.

What I mean by this is that let's just say the top of the air handler has an opening of 12 x 18, well the supply plenum that connects to it is 12 x18 so it must be large enough right?

My point is this, if the air handler is designed with a certain size opening and you attach a plenum that fits that size then obviously that unit was designed with the opening it was made with to flow the correct cfm. And therefore if you connect the same size plenum to it then it should flow correctly.

Or am I missing something?

[m kilgore]

Some manufactures require that you increase the plenum right away. The opening on the unit dosn't mean much as far as sizing the duct.

[Airmechanical]

yea, but better to be under alittle than oversized- IMHO

ya, if you don't mind sweating like a dog on those hot days



.

[Vampyreguy]

Wow, I have a 2680 square foot house so I thought I needed a 5 ton...
Did you spec your own equipment?:rules:

[sb023]

Vampyreguy,
I just mean I thought I needed it based on what was originally installed and I have had quite a few estimates and they have ALL recommended 5 tons.
I have even contacted a few people who come highly regarded on this site and over the phone they told me I need a 5 ton.
This is the very first person to tell me I needed less.
Why I find it interesting is that he sells Trane units.
I specifically told him when we met that I wanted the tax credit and that I had another a/c company out earlier that same day and they already told me that nothing Trane has in a 5 ton qualifies for the tax credit.

Don't you find that interesting the he was the ONLY one who said I need to downsize and he is the ONLY one who can't sell me a 5 ton.

I'm NOT saying he is right or wrong or his heat load was done right or wrong, but just funny how those circumstances played out.

[papa_jo]

ya, if you don't mind sweating like a dog on those hot days



.

run a litle longer would pull more moisture out of the air- if undersized

[beenthere]

Did your old unit run 24/7 when the ambient was at design temp. Or, did your old unit cycle on and off?

[tedkidd]

fix your ductwork

are you sure the design temps for the load calc were dialed in correctly

why don't you post the heat load calc

oversizing is bad, undersizing can be worse



.
We see over sized units all the time. I keep hoping to see an undersized one to hear from the homeowner what living with it is like.

Has anyone actually SEEN an undersized unit?

[DGIO-Not]

I can't post it because the contractor had it on his computer.
Maybe I could see if he would print it but I doubt it ?



Yes, have not read the whole thread. But there seems to be a big misunderstanding of Home Owners and contractors of what the difference is between a "free" estimate and work product.

Until you buy it, it is not yours. The best things in life are not free, you have a contractor willing to do the requiste homework to serve your best interest, but you are not entitled to that information until willing to commit.

As I have scrolled, this fact has maybe added to your confusion. Let me take that away, if they cannot show you how they came to their chosen recommendation, regardless of the system you have, then they are not offering a system that they can guarantee to be installed to Quality Installation Standards (where sizing is only a portion of.)

Sure, I will share our work product with you so you can share with my competitors, for a price...but why use a contractor not willing to learn or do the homework in the first place? Sometimes the cheapest contractor is the one who can address your cost of ownership in the first place, not necessarily the lowest price you are quoted today. Believe me the value and quality provided are starkly different.

[Airmechanical]

We see over sized units all the time. I keep hoping to see an undersized one to hear from the homeowner what living with it is like.

Has anyone actually SEEN an undersized unit?

the purpose of my post is inteneded specifically to answer the question

yes i actually have seen a few undersized system's in Tennessee

and trust me, the homeowners, are hating being hot, warm, not cool enough, call it what you like

in Tennessee, the old rule of thumb was 600 sq. ft/ton

over the years (global warming) causes that formula to be undersized

don't laugh, some companies (more than you would think) still size by rule of thumb



.

[Vampyreguy]

Vampyreguy,
I just mean I thought I needed it based on what was originally installed and I have had quite a few estimates and they have ALL recommended 5 tons.
I have even contacted a few people who come highly regarded on this site and over the phone they told me I need a 5 ton.
This is the very first person to tell me I needed less.
Why I find it interesting is that he sells Trane units.
I specifically told him when we met that I wanted the tax credit and that I had another a/c company out earlier that same day and they already told me that nothing Trane has in a 5 ton qualifies for the tax credit.

Don't you find that interesting the he was the ONLY one who said I need to downsize and he is the ONLY one who can't sell me a 5 ton.

I'm NOT saying he is right or wrong or his heat load was done right or wrong, but just funny how those circumstances played out.
sorry....just bein a smart azz :)