Need advice...new A/C tonage?

10 years ago

Hello all,
I have a 2400sqft 2 story house. I replaced the furnace two years ago with a 4 ton blower.
Now I have to replace the a/c unit and the evaporator coils. I currently have a 4 ton 12 seer unit but I guarantee you it's not working at full capacity. It is about 13 years old and I live in TEXAS. No a/c is big enough here. The current one runs all day long.
So I had two quotes. One offers me a 4 ton unit to match the blower and the other says I can handle a 5 ton unit since I'm replacing the coils.
Who is correct?
Should I change the ductwork (25 years old) to make the 5 ton more efficient?

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Comments (5)

mike_home
10 years ago
The best advice I can give is to find a contractor who will do a load calculation. Offering a size that is compatible with the furnace blower or coil makes no sense if it is the wrong size for the house.

The blower must supply enough air flow for the condenser. You need 350 - 400 CFM of air flow for each ton of cooling. The duct work should be evaluated. This may be a big source of your cooling problems.
tigerdunes
10 years ago
Agree with Mike...

3 issues here.

You must be sized correctly both furnace and AC.

You can not pair a 5 ton AC condenser with a furnace that only has a 4 ton rated blower.

And finally, if going up in condenser size, ductwork must e sized correctly both supply and return to move the conditioned air. Yes. A big deal.

IMO
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udarrell
10 years ago
Upsizing the A/C will not solve your problems.
You need to find someone to do a load-calc so you know what size is needed.

Then the install is everything along with the proper duct-system design for proper airflow to & from the rooms.

In the mean-time try doing some load-calcs with this Free Online whole house load-calc.

Here is a link that might be useful: Free Online whole house load-calc.
mlraff53
Original Author
10 years ago
I'm so confused. I was told that the duct work needed to be changed but it's not an emergency. There are no holes in them but they are original to the house. 25 yrs old.
I did the free online load cal and I have no idea what it means. I got:
total cooling BTU 7720
sensible load 6920

If I install a 5 ton compressor with the evaportator coils, is something going to happen to my blower (like freeze over) since it's only 4 tons.

Please understand that I don't know anything about a/c and I great appreciate all your help.

I want the most efficient unit for the least money.
I can do a 5 ton with coils now, or maybe a 4 ton with coils and maybe ductwork.
But I don't want to spend all this money if it's not going to save me any on my monthly bill.
tigerdunes
10 years ago
Obviously you did not perform the load calculation correctly.

I would try again.

Sorry.

You seem intent on going up in AC condenser size. I believe that's a mistake from the info you have provided. Look at your home's insulation properties for opportunity to improve.

Ductwork should have a thorough evaluation.

IMO