alwaysdiy

here are the questions to ask yourself.

1.have you seen your quoting dealers' load calcs in writing, in detail on the software letterhead?

2.what size is your current system?

3.how did it perform in AC cooling during the summer mths? did it handle the cooling load? did it ever run continuously? how would you describe indoor comfort level? what is your usual thermostat setting in the summer?

4.what size is your home?

5. current system is nat gas/AC or straight HP system?

if in doubt about sizing and lack confidence in your dealers to size correctly, then run the load calculation yourself. It costs $49 and can be performed fairly easily if you are reasonably computer savvy and intelligent. see link below.

I would not recommend purchasing a system that did not qualify for tax credit.

IMO

Here is a link that might be useful: Load Calc Software

I can give you a referral to a good contractor in your area if interested.

Thanks for the response. The house is about 2200 sq/ft above a half finish 1100 sq/ft basement. We are all electric with a 25 year 1 hp blower and a 11 year Goodman 3.5 ton heat pump. We keep the stat set at about 72 in the winter and around 77/78 in the summer. The current HP does not run all the time. Inside is fine, with the upstairs slightly warmer than the first floor. I'm sure that going to a variable speed will be a big help.

I don't really doubt the contractors load calclations. Although the last person I talked to gave me a heat load right at 34000 btu, but recommended using a 4 ton unit. His 4 ton 2 stage unit operates at 70% in first stage. That's 33600 btu, which is 98% of my 96 degree day. I guess I can understand some oversizing, but it seems that the 2 stage equipment is driving me to a full ton oversize.

Yes, I would love to have the name of somebody else in my area.

For what it's worth ENERGY STAR requires not more than 15% oversize on heatpumps for the cooling load and recommends 25% on heat loads - using the 99% temp range with the indoor thermostat at 75 for cooling.

It is typical for the thermostat cooling set-point to be 75, in at least one popular software program this is the default. Keeping that in mind, then get the 3 ton unit- even with the lower setpoint, you are sill under 36k for cooling.

Just opened up the references - 96 deg is the mean extreme and generally should not be used for load calculations - the 99% temp is 91 deg for Lousiville. Keep in mind an A/C has two jobs cooling the air (sensible load) and dehumidifying the air (latent load). If the unit is over-sized is runs shorter-cycles and does a poor job of dehumidifying and the space feels clammy - not comfortable.

Also keep in mind that those peak temperatures are for only a few hours a day on the hottest days on the year, meaning even if sized correctly it is still over-sized for 90% of the time it is running.

Check the AHRI ratings for the line/unit proposed.
www.ahridirectory.org

I have seen some '2 ton unit' actually rated at 2.1 or so and in '2.5 ton' in the same line actually rated at 2.4 - not as big a difference as you might think - the point being the 3 ton may have sufficient excess capacity anyway.

On my useful documents page; I have a few ACCA created helps for homeowners one a contractor scorecard and a few items on reading and evaluating Manual J inputs and results.

Here is a link that might be useful: useful documents page