I had another contractor come out today and perform a load calc (which I very much appreciate) and give a few quotes. I have an ac unit on the second floor that needs replacement. In the process of looking for its replacement, I found that cooling load for the house to be designed improperly. I must replace the second floor AC (coil and condenser). Anything beyond that is to improve the comfort (which is poor due to high humidity).

His analysis said that the current design of the two systems in the house are wrong. Today we have a 5-ton ac unit for the first floor/basement and a 2-ton unit for the second floor. His calculations say it should be 4 ton for the first/basement and 3 ton for the 2nd floor. I do think he did an accurate load calculation and it quantifies the "suspicions" and "guesses" of the other contractors who came and did not do a load calculation.

All and all, I like this contractor. He seems to know what he is doing. However, I suspect based upon other posts that I have seen, that he is really inflated on his pricing.

Here are the three quotes he gave to fix/replace the second floor unit. The current furnace is a 7.5 year old Carrier 58MCA single speed furnace.

Option # 1

Replace single speed blower in current furnace with VS speed blower (evergreen VS motor)

Carrier Performance 17 AC (24ACB736A003) 3 ton system

Carrier tin plated coil (CNPVP3617ATA)

Carrier 4" EZFLEX Media

Carrier Edge T-stat (STAT-TP-PRH)

new lineset and electric connections

10 year parts & 10 year labor

$6,597

Option # 2

Carrier Performance 17 AC (24ACB736A003) 3 ton system

Carrier tin plated coil (CNPVP3717ATA)

Carrier 95% 2 stage VS gas furnace (58UVB060-1-14) 60,00BTU

Carrier 4" EZFLEX media

Carrier Edge Thermidistat (STAT=TP-PRH)

new lineset and electric connections

10 year parts/10 years labor

$9,875

Option # 3

Carrier Infinity 21 3 ton AC (24ANB136A003)

Carrier tin coated coil (CNPV3617ATA)

Carrier Infinity 95% furnace 60,000BTU (58MVC060-1-14)

Carrier 4" EZFLEX media

Carrier Infinity controller (SYSTXCCUID01)

10 year parts / 10 year labor

$12,085

Option # 4

Carrier Infinity Inverter HP (25VNA036) 3 ton

Carrier Tin coated coil(CNPVP3717ATA)

Carrier Infinity Furnace 60,000BTU 95% modulating VS (58MVC060-1-14)

Carrier EXFLEX 4" Media

Carrier Infinity controller (SYSTXCCUID01)

10 year parts / 10 year labor

$15,033

He also offered similar packages for my 4 ton system for the 1st floor/basement. For the sake of space, I did not include these.

I live in Cincinnati in a newer built home that is fairly well insulated.

So, what does everyone think of these quotes? Would you consider modifying and existing single speed furnace to make it a VS? I have never heard of this before. It is an intriguing option, but I would like to know what some of the experts here think about it.

Michael