I just had a brand new 2008 goodman unit - complete condenser and coil. Yes it is on the roof but that's my only option. I have 1200 sf and vaulted ceilings. I believe we removed the 1 ton and put in a 2 ton. It cools off enough at night that AC isn't really needed until about 10AM then by noon a setting of 78 reads 80 and by 2pm it reads higher and the air isn't even cool anymore... by 5:30 its 85 on the reading though the front room is warmer than that. Finally when the sun has set it starts cooling off. The force of the air never really changes - its just that from 12-5:30 the air is warm and more or less not worth having on. I mean my fans are still on and it feels the same as if I hadn't made the investment. HELP? Is the 2 ton too small? Is it really the furnace fan? I've been told everything that it will always be 20 degrees cooler inside. But how can the air temp change so dramatically for 5 or so hours while the force is the same? Need advice...

Did you talk to the professional contractor that installed your equipment?

Did he take into consideration the fact that you have vaulted ceilings?

You have a design problem that should have been corrected.


A 1200 square foot home of normal construction will take 2 to 2 and a half tons. You have a different animal.

The air discharge stays the same but the temp will change because the return air temperature is going higher due to the heat load increasing.

I would contact a engineer or another HVAC company to do a ON SITE inspection since all we can do here is guess what your problems really are.

Thanks hvac1000
That's what I thought but he's told me various "technical" explanations - shouldn't it be cubic area vs. square footage when dealing with this footprint? I've spoke to them - yes, they came out once since the install, one week passed before coming out again - but today was almost 100 degrees and so I'm searching for more answers - hopefully the right ones. 1200 sq ft actually 600 at 25 feet and then 300 and 300 with regular close to std heights. Well they are coming again - then the city still has to come and inspect - perhaps their point of view will be useful. Oh... he said a 2.5 would freeze??

Oh... 300 is the open loft adjacent the 600 at 25ft. The other 300 is at std ceiling heights.
Yes the vents upstairs are a little weaker but not much - a little cooler but not much than below... right now its cooler outside after running AC all day! What a waste finanically and environmentally.

I'll be curious what they say tomorrow mid day - I'll take notes for sure.

I've heard it all

I mentioned this

Did he take into consideration the fact that you have vaulted ceilings?

I also mentioned this

A 1200 square foot home of normal construction will take 2 to 2 and a half tons. You have a different animal

Actually the salesman/installer should have done a manual J for the equipment size to start with.

Then they should have done a manual D for the correct duct work size and placement.

I have said this way to many times. Always get 2 or 3 estimates because you might actually find one of them that knows what they are doing.

Remember cold air falls like a rock no matter how much you try to blow up there it will never stay there. You are a prime candidate for a large high return air system to scrub that heat off the highest point. This will cause the system to draw the heat out of the upper level and replace it with cooler air.

Then you will be a happy camper. But remember that the equipment will still need to be sized by a manual J.

For your viewing pleasure.

HVAC Sizing Practice


EERE Consumer's Guide: Sizing Heating and Cooling Systems

I got 3 estimates - with huge ranges in price but with all the same recommendations - no one did a manual j or anything like that. From big name brand to a one man show type of company. This person actually recommended the most improvements w the best price too. Sounded knowledgeable. Thanks again for your input.

What makes a unit that is too big freeze - that is what he said last but wasn't for sure either.