Central AC tonnage

[paulcallaway]

Just moved into a stretched gardenia home , which has 2200 ft. Want to replace existing, original 3 ton AC , as it is 17 years old and don't want to wait for the summer when it may die. Does anyone have an idea if 3 tons is enough for this house, with North - South orientation and with extra, extra attic insulation ?
(Only 2 of us in the house, and we set the AC at 75.)
Thanks in advance to all who reply.

[retiredguy123]

I doubt it. A rough rule of thumb is that you need about a ton of cooling for every 600 square feet of living space. Also, an older house is not going to be as tight as a newer house, in terms of air leakage and the integrity of the attic insulation. You may get by with a 3.5 ton unit, but, you may need a 4 ton unit. You may want to compare your neighbors' houses to see what size units they have.

[Stu from NYC]

I would also contact a few A/C complanies and see what they suggest.

[Neils]

If the original 3 ton kept the house cool enough for 17 years, then you have your answer. I would up 1/2 ton to make sure.
Too large a unit for the house is not a good move either since the run time would be shorter, giving less humidity control.

[retiredguy123]

If the original 3 ton kept the house cool enough for 17 years, then you have your answer. I would up 1/2 ton to make sure.
Too large a unit for the house is not a good move either since the run time would be shorter, giving less humidity control.
I agree, but a lot of people set their thermostat at 78 or 80 degrees. I would definitely upsize at least a half ton.

[bagboy]

My advice would be to call Chuck Farrell AC and get their opinion, along with a quote.
352-633-9364.

[retiredguy123]

My advice would be to call Chuck Farrell AC and get their opinion, along with a quote.
352-633-9364.
I would get 3 quotes before deciding. Chuck Farrell and Munn's are both good companies. I am partial to Carrier units which Munn's installs, but Chuck Farrell doesn't. But, I wouldn't rely exclusively on what the contractor recommends about the size of the unit. They are going to provide a warranty on the equipment they install, but if they over or under size the system, they are not going to be responsible for that decision.

[John_W]

Chuck will probably be $1500 cheaper than the others, especially if you tell him to do it on his schedule since this is not an emergency. He will also be cheapest on repairs in the future. Just do a search and you'll see, the search botton is at the top and you look up any subject.

[biker1]

Ask the contractor to do a "Manual J" calculation on your home. If they don't know what this is then move on to another contractor.

Just moved into a stretched gardenia home , which has 2200 ft. Want to replace existing, original 3 ton AC , as it is 17 years old and don't want to wait for the summer when it may die. Does anyone have an idea if 3 tons is enough for this house, with North - South orientation and with extra, extra attic insulation ?
(Only 2 of us in the house, and we set the AC at 75.)
Thanks in advance to all who reply.

[DangeloInspections]

Ask the contractor to do a "Manual J" calculation on your home. If they don't know what this is then move on to another contractor.

biker1 hit the nail on the head. This is the only way to calculate the correct size. If you live in Sumter County the newer homes have the manual J for the home on their website, along with your blueprints, etc. If you have had any improvements done on the home like more insulation, enclosed a lanai, new windows, etc., you should have a new Manual J calculation done.

[retiredguy123]

biker1 hit the nail on the head. This is the only way to calculate the correct size. If you live in Sumter County the newer homes have the manual J for the home on their website, along with your blueprints, etc. If you have had any improvements done on the home like more insulation, enclosed a lanai, new windows, etc., you should have a new Manual J calculation done.
I agree with doing a new manual J calculation, but it is somewhat subjective. Also, you should consider your preferred thermostat setting. The OP's setting of 75 degrees would be a little on the low side. You may want to ask the sellers what temperature setting they used in the cooling season.

[dewilson58]

Might want to consider if you are going to expand (or enclose lanai) in the future.

[biker1]

You can specify the indoor temperature set point when doing a Manual J calculation. When combined with Manual S and Manual D, it is an objective way of doing things. There is a reason why new construction in FL requires a Manual J calculation; subjective estimates such as 600 square feet per ton may not work very well. Like everything else, it does require attention when specifying the characteristics (windows, insulation, orientation, etc.) of the house.

I agree with doing a new manual J calculation, but it is somewhat subjective. Also, you should consider your preferred thermostat setting. The OP's setting of 75 degrees would be a little on the low side. You may want to ask the sellers what temperature setting they used in the cooling season.