Air conditioner
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I am purchasing a newly built house with R15 insulation in the walls and R38 in the ceiling/attic. The house is 2 stories and 3400 square feet. The house is in the county SE of Charlotte NC. The front of the house faces S/SW. There is a 4 ton carrier 16 SEER single stage compressor. The unit is set up with dual zones, first and second floor. Will this unit and set up be able to cool that large of a house? From everything I have read it would need a 5 ton unit. I assume in the peak of the summer when its 90-100 and humid that this unit will not be able to cool the entire house. There will be six people and a dog living in it. kids with electronics and computer running.
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Replies
>"The house is 2 stories and 3400 square feet."
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>"There is a 4 ton carrier 16 SEER single stage compressor."
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>"Will this unit and set up be able to cool that large of a house?"
Unless there is a large expanse of west-facing window a 4-tonner is probably OVERSIZED rather than undersized. It probably would be more comfortable & efficient with a 3-tonner, or even 2.5 tons(!).
Take a look at this graphic plotting square feet per ton against house size on a few dozen Manual-J's performed by Energy Vanguard (Decatur GA):
https://beta.greenbuildingadvisor.com/app/uploads/sites/default/files/images/Bailes_graph_for_Manual_J_blog.preview.png
Only the very worst performing house in the 3000-4000' range had a ratio of a ton per 900' (which is about where your house is, with 3400'/4 tons= 850' per ton.) The middle range for houses that size is about a ton per 1400'. That would make your best fit more likely to be (3400'/1400' =) ~2.5 tons, give or take.
See the full article here:
https://www.greenbuildingadvisor.com/article/manual-j-load-calculations-vs-rules-of-thumb
Oversizing is the enemy of comfort & efficiency. Unless you're running a server farm for an ultra-busy web service or something your cooling load won't be anywhere near 5 tons. The more likely comfort problem to expect would be higher than desirable indoor humidity due to an oversized 4 tonner running too low a duty cycle for the ~2.5 ton load, even at 102F (= ten degrees higher than the 1% outside design temp for Charlotte NC.)
For yuks this summer you might want to measure the duty cycle on afternoons when it's going to be north of 90F to get a sense of just how oversized the equipment is:
https://www.greenbuildingadvisor.com/article/how-to-tell-if-your-air-conditioner-is-oversized