Paired with what model furnace?...how did your old systems perform, specifically run times, CPH, and satisfying your comfort?... Without a professionally performed load calc, any answer here would be guessing.

IMO

thanks for responding. Both did load calculations. The contractor with the two 3 ton units did measure every room, window, spent time in the attic. He was here for a few hours. The contractor with the 4 ton and 2 ton, did some slight measuring, did not measure windows, did not measure every room, did not spend as much time in the attic. Furnaces: 4 ton-CH33-50/60C-2F SL280UH090V60C. 2 ton- CH33-31A-2F SL280UH070V36A for the 3 tons CH33-43B2F SL280UH090V36B using the 7500 thermostats with both contractors. I don't have any copies of either load calculations. The 700 sq ft side is master bdrm, the 2.5 ton had problem cooling at the height of summer, put in temp control gable fan which made a huge difference and room more comfortable. Room also backs up to garage which attic space is not insulated, walls probably are not as well but not sure.

As for run times, the 3.5 set at 79-80 in peek summer would run probably 15-20 minutes, cycle off for about 10 and kick back on for the 1400 sq ft. For the 700 sq ft during the day set at 80, for sleeping it would be set at 77 and run most of the time, cycle off for about 5 minutes then kick right back on. Both are Goodman 1 stage one is a 12 SEER the other a 10 SEER and they are 15 years old.

contractor 1, who spent the most time on load calculations said his software is showing that a 2 ton may not be enough at the peek of summer. Since Lennox does not make .5 ton sizes this is why he would rather go to a 3 ton system. contractor 2, is saying it is overkill and it would short cycle. Contractor 1, does not believe it will short cycle, but will just run in the lower stage for most of the time since it is a two stage system. He said if it short cycles and is not the right unit he will replace it with something else on his dime. Both are reputable contractors who do excellent installation practices and great warranties on parts and labor.

Had a home energy audit, insulation is very sound in all of the home. Only leaks are at the ducts and sheet rock, they suggested sealing ducts. Garage attic is not insulated and this space is open to the attic space of the master. Part of the 700 sq ft is also a den, which could be a 3 bay garage in other homes, the adjoining wall to the garage and so is one of the master suit walls.

I would get the load calc from dealers in writing on the software letterhead. And compare. Study the design temps both dealers used both in and out. Another part of this is that the dealers are having to oversize you on the furnaces. I will assume that humidity is not an issue for your location.

IMO

Not questioning integrity of contractors but do keep in mind that typically they will favor a brand and will push the brand b/c of getting quantity dealer disc. So larger profit margin on job. Also, the more they work with one brand the more familiar and better job they do so there is a plus to favoring one brand over others, not just a $ thing.

I requested the load calculation from each contractor. I heard back from contractor 2 who was the person with the 4 and 2 ton unit. He said he doesn't provide load calculations until after you buy from him and it's installed. Probably will get a response from contractor 1 tomorrow. I agree with bossyvossy, I'm sure some of this is based on what they have sitting in the warehouse. Just want to make sure I get the right unit for me, not for them.....

Contractor 2 ended up sending the load calculations, he must have thought better about his initial response. Contractor 1 had no problems sending them and even followed up with a phone call to explain why his came out they way they did. I will attempt to provide accurate info to you below.

Contractor 1: 1190 sq ft with load calculation of 28691 for main portion of the home which is north facing. 736 sq ft with load calculation of 28059 which is 3 sides of house south facing. Also exposed to garage attic space which is not insulated. and Many large windows and doors that are SE, S, and SW facing for that small space. He does not figure in cooling the wall space. His total sq ft is 1,926. My home's actual sq ft is 2158. This contractor measured every room, window, ceiling height and spent a lot of time in attic.

Contractor 2: 1369 sq ft with a load calculation of 36,009 for main part north side of house and 814 sq ft with load calculation of 18,874 for south side of house. His total sq footage is 2183. He did not measure every room, window or ceiling, my ceilings vary from vaulted to 8 ft. Small side of house is 80 vaulted along with being south facing. If he measured he measured anything it was from the outside of the home. He did spend time in the attic, but no where near the time as Contractor 1.

One more comment to tigerdunes. Not sure why the furnace would be over sized. I rarely use heat, but I understand that the furnace blower is important to the efficiency of the units. Rarely do we have an issue with humidity in my area of Arizona. The times we have a little humidity it is actually appreciated.

For example, the Lennox furnaces quoted are oversized. If you need a 4 ton AC condenser, then you must have a 4 ton rated blower on the furnace. That's why it is even more important to get condenser sizing correct. If dealer #2 is correct, it seems a 3 ton and 2 ton would be the right size condenser. But I would not go with him until he gives you the load calc in writing.

IMO

Tigerdunes, I questioned Contractor 2 why he is using a 5 ton coil and furnace for a 4 ton unit. He said that it is a variable speed furnace and it allows him to adjust it to the need, he can actually ramp it down to a 3 ton unit if necessary. It is more flexible, so he says.

Both contractors gave me the load calculations in writing. Problem is they are not similar in thought, which is what is causing my confusion. They are priced within only a few hundred of each other and the installation is exactly the same, both with good reputations. It comes down to the load calculations and what units to use.

the thing about the load numbers you've been given is what are the design temperatures? This will have a big impact on the numbers. Are you up in the mountains where it snows or down where it routinely gets above 110*?

I'm in the valley where it gets above 110*. Both have the outdoor temp set at 108 and indoor at 75. But one has the humidity factor at -10 the other at -8.

We have about 115 days over 100* and about 11 to 18 days of over 110*. We don't cool down at night, lucky if it is just below 100*. High heat of the day is around 5 pm, then the radiant heat from the ground last for hours. The little cool down we do get is around 3 am and we are on our way to warming up by 9am in the summer.

First contractor, I would run from