A/C question

[CEHollier]

As I understand the industry rule of thumb for a central unit (12-14 seer) it is 1 ton for every 500 sq ft. This is for regular construction not multiple window walls, 20 ft ceilings, etc. For a 1,620 sq ft area with 10-11 foot ceilings with minimal west wall exposure and energy effecient insulated windows would a 12-14 seer 3.5 ton unit be adequate?

Thanks,
Charles

 

[jrfount]

Technically you should us an AC load calculator to properly size your air. Realistically 3.5-4 tons should work just fine as long as you don't intend to ever expand. Personally I would probably size a 4ton it gets hot in La. That extra .5 tons shouldn't cause any excess moisture build up in your house but it just may make your Augusts feel a little cooler.

 

[CEHollier]

Well, long story but I sold my home two months ago. The guy calls me telling me it is undersized and not cooling like it should. He's trying to clain there was a problem and I didn't disclose it. When I built the house 13 years ago the architect speced out two 3 ton units. I bumped the common area up half a ton because of kids in-out of the house etc. With 3.5 tons my wife wore sweats in August because it cooled that well. I do not see how he has a leg to stand on claiming I undersized the unit. It is 13 yo and probably crapped out and now he wants me to buy him a new one. The house was bought "as is" and his inspector reported that coil was corroded and soon to fail. Go figure

 

[kcinnick]

I have a 4 ton unit on a 2500 sq foot house with vaulted ceilings in a very large living area and it seems to keep the house at 72 except on those few 100 degree days we had.

When I lived in a 1300sf duplex we had a 2.5 ton that would freeze your but off any day of the week.

I know this isn't scientific, but seems like 3-3.5 would be more than adequate from my experiences.

 

[jrfount]

3.5 ton is certainly not undersized based on industry standards. I don't think he would have much of a leg to stand on either, also considering the recent heat wave a lot of people suddenly think something is wrong with their AC they expect 30F+ cooling over ambient and a properly sized unit just cant do that. Especially not on a 13 year old house. Insulation compresses, caulk cracks, windows start to leak etc.

 

[jrfount]

I have a 4 ton unit on a 2500 sq foot house with vaulted ceilings in a very large living area and it seems to keep the house at 72 except on those few 100 degree days we had.

When I lived in a 1300sf duplex we had a 2.5 ton that would freeze your but off any day of the week.

I know this isn't scientific, but seems like 3-3.5 would be more than adequate from my experiences.

This is where the load calculators I mentioned comes into play. Foam insulation, spray cellulose, spray fiber, or batts they all make a difference. Brick, vinyl, stucco, lap board yep they matter. How many windows on the sun sides of the house? How many square feet of exposed wall? Low E, double or single pane? Slab or crawlspace? Etc, etc, etc. It is possible to have a 1300sqft house that a 4 ton unit can't keep up with. It is also possible with the right materials to cool 1500sqft with a 2 ton unit. But as a roundabout using the 500sqft method I was always taught to round up to the higher 1/2 ton unit. Just my .02.

 

[DuckYou]

You do have to calculate the load specific for all areas. There is so much that goes into a proper a/c, and most contractors or architects just use that same BS figure of 1 ton for every 500 sq/ft.

The home owner will have no recourse if the house was sold "As-Is" and they had seen the unit. Since there was an inspection, that proves they knew the size and specs of the unit.

 

[CEHollier]

3.5 ton is certainly not undersized based on industry standards. I don't think he would have much of a leg to stand on either, also considering the recent heat wave a lot of people suddenly think something is wrong with their AC they expect 30F+ cooling over ambient and a properly sized unit just cant do that. Especially not on a 13 year old house. Insulation compresses, caulk cracks, windows start to leak etc.

I agree. But even with hot summers it cooled well. Even on 100 degree days it was more than adequate. He has no claim if it failed because he bought it "as is". I think he talked to an attorney and was told to try the failure to "disclose" it was undersized and there was a problem. I'm not sure what his angle is but he's SOL if he thinks I'm coughing up any money. I have a patient that is an attorney and explained the situation to her. She laughed and said to tell them to "bring it on". Naturally I don't want it to come to that but I will if forced to. People never cease to amaze me.